@article{narsipur_ramesh_gopalarathnam_edwards_2023, title={Discrete vortex modeling of perching and hovering maneuvers}, ISSN={["1432-2250"]}, DOI={10.1007/s00162-023-00653-2}, journal={THEORETICAL AND COMPUTATIONAL FLUID DYNAMICS}, author={Narsipur, Shreyas and Ramesh, Kiran and Gopalarathnam, Ashok and Edwards, Jack R.}, year={2023}, month={May} }
@article{johnson_jenquin_mccready_narayanaswamy_edwards_2022, title={Experimental Investigations of the Hypersonic Stream-Traced Performance Inlet at Subdesign Mach Number}, volume={61}, ISSN={["1533-385X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85144482289&partnerID=MN8TOARS}, DOI={10.2514/1.J062113}, abstractNote={Stream-traced inlets offer superior compression efficiency for scramjet engines and are strong prospects for practical application. However, only limited experimental information is available on the subdesign performance of these inlets. In this study, the operation of a stream-traced truncated-Busemann inlet with a design point of Mach 5.5 and a physical contraction ratio of [Formula: see text] is experimentally investigated in a Mach 4.0 flow. Several nonintrusive flow measurement techniques are employed to provide a thorough understanding of the intricate flowfield within these inlets at various operation conditions. The measurements include surface pressure, mean streak-line patterns, off-body velocity fields, and qualitative gas density fields. Together, these datasets provided a unique understanding of the flow evolution and load distribution within the inlet and isolator with and without application of an external backpressure. The facility effects on the inlet operation are also explored. Without appropriate boundary-layer conditioning, the wind-tunnel starting shock could not be swallowed by the inlet; this is termed a “failed start” operation. During the failed start operation the inlet flowfield and surface pressure field, even without external backpressure, exhibited strong similarities with an unstarted inlet. The failed start operation enabled a unique lens to the flowfield in the unstarted inlet throat that could not be otherwise obtained due to optical constraints.}, number={1}, journal={AIAA JOURNAL}, author={Johnson, Ethan and Jenquin, Chase and McCready, Jonathan and Narayanaswamy, Venkat and Edwards, Jack}, year={2022}, month={Sep} }
@article{narsipur_gopalarathnam_edwards_2022, title={Low-Order Modeling of Dynamic Stall on Airfoils in Incompressible Flow}, ISSN={["1533-385X"]}, DOI={10.2514/1.J061595}, abstractNote={Airfoil dynamic stall in incompressible flow is characterized by two interacting viscous flow phenomena: time-varying trailing-edge separation and the shedding of intermittent leading-edge-vortex structures. In the current work, a physics based low-order method capable of modeling the interactions between the two flow phenomena is developed with the aim of predicting dynamic stall with only a few empirical tuning parameters. Large computational datasets are used to understand the flow physics of unsteady airfoils so as to augment an inviscid, unsteady airfoil theory to model the time-dependent viscous effects. The resulting model requires only three empirical coefficients for a given airfoil and Reynolds number, which could be obtained from a single moderate-pitch-rate unsteady motion for that airfoil/Reynolds number combination. Results from the low-order model are shown to compare excellently with computational and experimental solutions, in terms of both aerodynamic loads and flow-pattern predictions. In addition to formulating a method with limited empirical dependencies, the current research provides valuable insights into the flow physics of unsteady airfoils and their connection to rapidly predictable theoretical parameters.}, journal={AIAA JOURNAL}, author={Narsipur, Shreyas and Gopalarathnam, Ashok and Edwards, Jack R.}, year={2022}, month={Sep} }
@article{hash_drummond_edwards_kato_lee_2022, title={Numerical simulation of stable and unstable ram-mode operation of an axisymmetric ethylene-fueled inlet-isolator-combustor configuration}, volume={242}, ISSN={["1556-2921"]}, DOI={10.1016/j.combustflame.2022.112157}, abstractNote={Large-eddy simulations of stable and unstable ramjet operational modes are presented for an axisymmetric inlet-isolator-combustor configuration experimentally tested in the University of Illinois's ACT-II arc-heated combustion tunnel. A 32 species ethylene oxidation mechanism including nitrous oxide formation reactions is used in the calculations (HyChem FFCM 2.0). Conjugate heat-transfer models based on an assumed penetration depth of the applied heating load are used to account for localized wall heating during the short durations (∼0.2 to 0.3 s) of the parts of the experiments simulated in this work. The results show a marked sensitivity to trace levels of atomic oxygen (∼1% by mass) in the free stream, a consequence of the arc-heating process. Atomic oxygen significantly reduces ignition delay at the relatively low pressures present within the configuration. With 1% atomic oxygen in the free stream, a jet-wake stabilized, partially-premixed flame structure emerges during thermal-throat ramjet operation at an equivalence ratio of 1.24, in accord with available experimental pressure and imaging measurements. Considering the free stream as pure air results in a cavity-wake stabilized, rich premixed flame. Simulations of unstable ram-mode operation leading to inlet unstart at an equivalence ratio of 1.97 also indicate a sensitivity to the free-stream composition. A reduction in atomic oxygen concentration to 0.8% by mass yields good agreement with the experimentally-observed isolator shock-train propagation speed. Both the computational and experimental results indicate that the shock train accelerates before being disgorged from the inlet. This acceleration stems from a rapid increase in the sizes of regions of low speed, sometimes separated flow behind Mach disks that form as the shock train proceeds upstream.}, journal={COMBUSTION AND FLAME}, author={Hash, Caleb A. and Drummond, Paige M. and Edwards, Jack R. and Kato, Nozomu and Lee, Tonghun}, year={2022}, month={Aug} }
@article{hirato_shen_gopalarathnam_edwards_2021, title={Flow criticality governs leading-edge-vortex initiation on finite wings in unsteady flow}, volume={910}, ISSN={["1469-7645"]}, DOI={10.1017/jfm.2020.896}, abstractNote={Abstract}, journal={JOURNAL OF FLUID MECHANICS}, author={Hirato, Yoshikazu and Shen, Minao and Gopalarathnam, Ashok and Edwards, Jack R.}, year={2021}, month={Jan} }
@article{nielsen_edwards_chelliah_lieber_geipel_goyne_rockwell_cutler_2021, title={Hybrid Large Eddy Simulation/Reynolds-Averaged Navier-Stokes Analysis of a Premixed Ethylene-Fueled Dual-Mode Scramjet Combustor}, volume={59}, ISSN={["1533-385X"]}, DOI={10.2514/1.J059343}, abstractNote={Hydrocarbon fuels offer optimal high energy per volume for scramjet applications for sustained hypersonic flight but require additional residence time due to slower ignition delays (compared with hydrogen fuel). The injection of ethylene at the start of the isolator of a dual-mode scramjet combustor, operating in ramjet mode, allows sufficient mixing to achieve efficient premixed turbulent combustion. A cavity flameholder anchors the flame, supplying sufficient radicals to sustain a stable flame in the high-speed environment. This work investigates flame structure and stabilization limits of a new configuration with a scaled-down cavity embedded in the flow path of the combustor with a strut and insert. The cavity is reduced in size by one-third to enable eventual direct numerical simulations of the flame stabilization process. This work, however, focuses on modeling the full isolator/combustor geometry using a hybrid large eddy simulation/Reynolds-averaged Navier–Stokes simulation strategy. Particle image velocimetry, planar laser-induced fluorescence, coherent anti-Stokes Raman spectroscopy, and pressure measurements are compared with numerical predictions to analyze and characterize the conditions within the combustor, including flame structure, flow velocities, species composition, and wall pressure. An adjustable air throttle in the extender is able to control the placement of the shock train in the isolator and maintain a stable flame at various equivalence ratios. The simulations show reasonably good agreement with the experimental scalar and velocity data and predict a flame angle consistent with premixed turbulent flame-speed correlations.}, number={7}, journal={AIAA JOURNAL}, author={Nielsen, Tanner B. and Edwards, Jack R. and Chelliah, Harsha K. and Lieber, Damien and Geipel, Clayton and Goyne, Christopher P. and Rockwell, Robert D. and Cutler, Andrew D.}, year={2021}, month={Jul}, pages={2440–2456} }
@article{tonelli_edwards_2020, title={Are poly(p-phenylene terephthalamide) (Kevlar (R)) and other liquid crystalline polymers conformationally rigid?}, volume={193}, ISSN={["1873-2291"]}, DOI={10.1016/j.polymer.2020.122342}, abstractNote={In a series of papers beginning in the 1950s, Flory, and later Flory and Ronca, and Yoon, Ronca, Bruckner et al. theoretically derived and described the Statistical Mechanics of rodlike particles and semi-flexible chain molecules. Their work was based on a Lattice-Model whose free-energy was separable into independent terms:a mixing term depending on concentration and an athermal disorientation term depending on the equilibrium flexibility of the chain molecules. They eventually added energetic interactions between the rodlike particles to the disorientation partition function, and also considered aromatic polyesters with mesogenic phenyl rings and attached ester bonds separated by inherently flexible polymethylene segments. To treat the thermotropic aromatic polyesters, Yoon, Ronca, Bruckner et al. added an independent conformational partition function to account for the loss of conformations required for extension of the polymethylene segments to form liquid crystals. Though these treatments achieved various degrees of agreement with experimental observations of liquid crystalline polymers, in all cases the mesogenic backbone segments were assumed to be rigid with extended conformations. Their inherent flexibilities were never considered. Here we demonstrate that the mesogenic backbone segments may in fact not be inherently rigid, but instead conformationally flexible. As an example, we show that Kevlar® [poly-1,4-phenylene (terephthalamide)] remains extended enough and sufficiently anisotropic to be liquid crystalline even though its 1,4-linked backbone phenyl rings are conformationally flexible.}, journal={POLYMER}, author={Tonelli, Alan E. and Edwards, Jack F.}, year={2020}, month={Apr} }
@article{edwards_nielsen_2020, title={Mesh-Sequenced Realizations for Evaluation of Subgrid-Scale Models for Turbulent Combustion}, volume={58}, ISSN={["1533-385X"]}, DOI={10.2514/1.J059217}, abstractNote={This paper develops a new approach for analysis of subgrid closures for turbulent combustion as modeled using direct quadrature (finite-rate chemistry) techniques. The approach, termed multiresolution analysis through mesh-sequenced realizations (MRA-MSR), conducts simultaneous, constrained large-eddy simulations on a set of hierarchically coarsened meshes. The availability of underlying fine-mesh (subgrid) data corresponding to coarse-mesh locations allows a clearer assessment of the effects of unresolved fluctuations on apparent reactivity. A key to MRA-MSR is the correlation of eddy structures at coarser mesh levels, which is facilitated by the transfer of filtered fine-mesh velocity information. A seven-mesh MRA-MSR hierarchy using three resolution levels is applied to one of the Sydney bluff-body stabilized methane–hydrogen flames. Analysis of the simultaneously evolved data at different resolution levels reveals several interesting trends. First, at high Damköhler numbers, there is clear evidence of attenuation of apparent reactivity due to the effects of unresolved fluctuations. Secondly, single-point, single-time filtered density functions of a normalized subgrid Damköhler number show a characteristic beta probability density function (PDF) form and display evidence of scale similarity. Interrogation of the MRA-MSR database also shows that the recently-proposed least-squares minimization (LSM) turbulence–chemistry interaction model can account for the observed diminishment in reactivity at high Damköhler numbers but cannot reduce scatter significantly. A new form of the LSM model, which makes use of the normalized subgrid Damköhler number beta PDF distribution, performs slightly better than the original model, illustrating the potential of MRA-MSR both in assessing existing closure concepts and in developing new ones.}, number={11}, journal={AIAA JOURNAL}, author={Edwards, Jack R. and Nielsen, Tanner B.}, year={2020}, month={Nov}, pages={4878–4892} }
@article{narsipur_hosangadi_gopalarathnam_edwards_2020, title={Variation of leading-edge suction during stall for unsteady aerofoil motions}, volume={900}, ISSN={["1469-7645"]}, DOI={10.1017/jfm.2020.467}, abstractNote={Abstract}, journal={JOURNAL OF FLUID MECHANICS}, author={Narsipur, Shreyas and Hosangadi, Pranav and Gopalarathnam, Ashok and Edwards, Jack R.}, year={2020}, month={Oct} }
@article{patton_edwards_2019, title={Least Squares Minimization Closure Models for LES of Turbulent Combustion}, volume={102}, ISSN={["1573-1987"]}, DOI={10.1007/s10494-018-9968-5}, number={3}, journal={FLOW TURBULENCE AND COMBUSTION}, author={Patton, Conrad H. and Edwards, Jack R.}, year={2019}, month={Mar}, pages={699–733} }
@article{narsipur_gopalarathnam_edwards_2019, title={Low-Order Model for Prediction of Trailing-Edge Separation in Unsteady Flow}, volume={57}, ISSN={["1533-385X"]}, DOI={10.2514/1.J057132}, abstractNote={Computational and experimental results for pitching and plunging airfoils were used to study the time lag associated with boundary-layer convection and to develop a model that can be used to augment inviscid theoretical methods for unsteady airfoil flows to include the effects of trailing-edge separation and unsteady stall. Computations using an unsteady Reynolds-averaged Navier–Stokes code were used to obtain results for airfoils in steady flow and for several pitch and plunge motions. The motions were selected such that stall occurred only due to trailing-edge separation without leading-edge vortex formation. Viscous corrections to inviscid airfoil theory are first calculated in steady flow by implementing a nonlinear decambering flap to model the effect of the separated boundary layer. A leading-edge suction parameter, from earlier research, is used to connect the aerodynamic state in unsteady motion with a steady-state condition. Computational results showed that the differences in aerodynamic loads between steady and unsteady flows can be attributed to the boundary-layer convection lag, which can be modeled by choosing an appropriate value of a time-lag parameter . To provide appropriate viscous corrections to inviscid unsteady calculations, the nonlinear decambering flap is applied with a time lag determined by the value, which was found to be essentially independent of motion kinematics for a given airfoil and Reynolds number. The predictions of the aerodynamic loads, unsteady stall, hysteresis loops, and flow reattachment from the low-order model agree well with computational fluid dynamics and experimental results, both for individual cases and for trends between motions. The model was also found to perform as well as existing semi-empirical models while using only a single empirically defined parameter.}, number={1}, journal={AIAA JOURNAL}, author={Narsipur, Shreyas and Gopalarathnam, Ashok and Edwards, Jack R.}, year={2019}, month={Jan}, pages={191–207} }
@article{bornhoft_edwards_lin_2019, title={Numerical Simulation of Two-Phase Flow Within Aerated-Liquid Injectors}, volume={35}, ISSN={["1533-3876"]}, DOI={10.2514/1.B37284}, abstractNote={Aerated-liquid atomization involves the injection of a small amount of gas into a liquid stream to initiate primary breakup within the injector itself. The sprays that result have good penetration ...}, number={6}, journal={JOURNAL OF PROPULSION AND POWER}, author={Bornhoft, Brett J. and Edwards, Jack R. and Lin, Kuo-Cheng}, year={2019}, pages={1034–1047} }
@misc{edwards_2019, title={Reflections on the early development of the "AUSM family" of Riemann solvers}, volume={29}, ISSN={["1432-2153"]}, DOI={10.1007/s00193-018-0863-8}, number={5}, journal={SHOCK WAVES}, author={Edwards, J. R.}, year={2019}, month={Jul}, pages={601–609} }
@article{hirato_shen_gopalarathnam_edwards_2019, title={Vortex-Sheet Representation of Leading-Edge Vortex Shedding from Finite Wings}, volume={56}, ISSN={["1533-3868"]}, DOI={10.2514/1.C035124}, abstractNote={A characteristic feature of flows past many oscillating airfoils and wings is the leading-edge vortex (LEV). Although considerable progress has been made in the low-order modeling of LEV formation over airfoils, the prediction of LEV formation on finite wings remains a challenge. A low-order method is presented for modeling the formation of the LEV on finite wings. An unsteady vortex-lattice method has been augmented to model the effect of the LEV, which is modeled as a vortex sheet. The criticality of leading-edge suction is used to modulate the formation of the LEV at different spanwise locations of the wing. This feature enables prediction of the spanwise location of the LEV onset and the subsequent nonuniform growth of the LEV on the wing. A good comparison of the predicted flow features is seen with results from a higher-order Reynolds-averaged Navier–Stokes code. The predicted forces are also in reasonable agreement. The LEV sheet model has the potential to be used in a variety of low-order methods for rapid prediction of unsteady finite-wing aerodynamics.}, number={4}, journal={JOURNAL OF AIRCRAFT}, author={Hirato, Yoshikazu and Shen, Minao and Gopalarathnam, Ashok and Edwards, Jack R.}, year={2019}, pages={1626–1640} }
@article{rockwell_goyne_chelliah_mcdaniel_rice_edwards_cantu_gallo_cutler_danehy_2018, title={Development of a Premixed Combustion Capability for Dual-Mode Scramjet Experiments}, volume={34}, ISSN={["1533-3876"]}, DOI={10.2514/1.b36550}, abstractNote={Hypersonic airbreathing engines rely on scramjet combustion processes, which involve high-speed, compressible, and highly turbulent reacting flows. The combustion environment and the turbulent flames at the heart of these engines are difficult to simulate and study in the laboratory under well-controlled conditions. Typically, wind-tunnel testing is performed that more closely approximates engine development rather than a careful investigation of the underlying physics that drives the combustion process. The experiments described in this paper, along with companion datasets, aim to isolate the chemical kinetic effects and turbulence–chemistry interaction from the fuel–air mixing process in a dual-mode scramjet combustion environment. A unique fuel-injection approach is adopted that produces a uniform fuel–air mixture at the entrance to the combustor and results in premixed combustion. This approach relies on the mixing enhancement of a precombustion shock train upstream of the dual-mode scramjet’s combustor. For the first time, a stable flame, anchored on a cavity flameholder, is reported for a scramjet combustor operating in premixed fuel–air mode. The new experimental capability has enabled numerous companion studies involving advanced diagnostics such as coherent anti-Stokes Raman scattering, particle image velocimetry, and planar laser-induced fluorescence.}, number={2}, journal={JOURNAL OF PROPULSION AND POWER}, author={Rockwell, Robert D. and Goyne, Christopher P. and Chelliah, Harsha and McDaniel, James C. and Rice, Brian E. and Edwards, Jack R. and Cantu, Luca M. L. and Gallo, Emanuela C. A. and Cutler, Andrew D. and Danehy, Paul M.}, year={2018}, month={Mar}, pages={438–448} }
@article{ramesh_granlund_ol_gopalarathnam_edwards_2018, title={Leading-edge flow criticality as a governing factor in leading-edge vortex initiation in unsteady airfoil flows}, volume={32}, ISSN={["1432-2250"]}, DOI={10.1007/s00162-017-0442-0}, abstractNote={A leading-edge suction parameter (LESP) that is derived from potential flow theory as a measure of suction at the airfoil leading edge is used to study initiation of leading-edge vortex (LEV) formation in this article. The LESP hypothesis is presented, which states that LEV formation in unsteady flows for specified airfoil shape and Reynolds number occurs at a critical constant value of LESP, regardless of motion kinematics. This hypothesis is tested and validated against a large set of data from CFD and experimental studies of flows with LEV formation. The hypothesis is seen to hold except in cases with slow-rate kinematics which evince significant trailing-edge separation (which refers here to separation leading to reversed flow on the aft portion of the upper surface), thereby establishing the envelope of validity. The implication is that the critical LESP value for an airfoil–Reynolds number combination may be calibrated using CFD or experiment for just one motion and then employed to predict LEV initiation for any other (fast-rate) motion. It is also shown that the LESP concept may be used in an inverse mode to generate motion kinematics that would either prevent LEV formation or trigger the same as per aerodynamic requirements.}, number={2}, journal={THEORETICAL AND COMPUTATIONAL FLUID DYNAMICS}, author={Ramesh, Kiran and Granlund, Kenneth and Ol, Michael V. and Gopalarathnam, Ashok and Edwards, Jack R.}, year={2018}, month={Apr}, pages={109–136} }
@article{zilberter_edwards_wittich_2017, title={Numerical Simulation of Aero-Optical Effects in a Supersonic Cavity Flow}, volume={55}, ISSN={["1533-385X"]}, DOI={10.2514/1.j055402}, abstractNote={A hybrid large-eddy simulation/Reynolds-averaged Navier–Stokes turbulence model is applied to compute the wave-front aberrations in an optical beam passing through a supersonic open cavity flow. Th...}, number={9}, journal={AIAA JOURNAL}, author={Zilberter, Ilya A. and Edwards, Jack R. and Wittich, Donald J., III}, year={2017}, month={Sep}, pages={3095–3108} }
@article{ke_edwards_2017, title={Numerical Simulations of Turbulent Flow over Airfoils Near and During Static Stall}, volume={54}, ISSN={["1533-3868"]}, DOI={10.2514/1.c034186}, abstractNote={Reynolds-averaged Navier–Stokes and hybrid large-eddy/Reynolds-averaged Navier–Stokes simulations of turbulent flow past an Aérospatiale A-Airfoil near stall at , , and a NACA 0012 airfoil under static stall conditions (, , ) are described in this paper. In the flow past the A-Airfoil, comparisons with surface skin-friction coefficient and pressure coefficient distribution are generally in good agreement with experimental measurements. Comparisons with experimental velocity profile data and Reynolds-stress data are also generally favorable. Leading-edge laminar separation and turbulent reattachment is predicted when the Menter–Langtry correlation-based transition model is used in combination with either Reynolds-averaged Navier–Stokes or large-eddy/Reynolds-averaged Navier–Stokes strategies, but the level of trailing-edge separation is underpredicted, relative to experimental data and to results obtained without the inclusion of transition model. For the case of flow past a NACA 0012 airfoil under static stall conditions, results from the large-eddy/Reynolds-averaged Navier–Stokes simulations exhibit a sensitivity to mesh refinement, with finer spanwise mesh resolution leading to light stall, characterized primarily by trailing-edge separation, and coarser spanwise mesh resolution leading to deep stall, characterized by the presence of a stabilized leading-edge vortex. Calculations that include wind-tunnel wall effects show better general agreement with experimental measurements but also display the aforementioned sensitivity to spanwise mesh refinement.}, number={5}, journal={JOURNAL OF AIRCRAFT}, author={Ke, Jianghua and Edwards, Jack R.}, year={2017}, month={Sep}, pages={1960–1978} }
@article{busa_rice_mcdaniel_goyne_rockwell_fulton_edwards_diskin_2016, title={Scramjet Combustion Efficiency Measurement via Tomographic Absorption Spectroscopy and Particle Image Velocimetry}, volume={54}, ISSN={["1533-385X"]}, DOI={10.2514/1.j054662}, abstractNote={The combustion efficiency of a scramjet is a metric that evaluates the overall performance of the engine. Until recently, combustion efficiency was measured using indirect approaches such as a one-dimensional control volume calculation or a calorimeter and wall pressure tap measurements. A novel nonintrusive direct approach for the measurement of combustion efficiency is presented that combines the optical diagnostic techniques tunable diode laser absorption tomography and stereoscopic particle image velocimetry. Experimental results are presented for measurements of the University of Virginia’s Supersonic Combustion Facility in both the scram and ram-modes of operation. The tunable-diode-laser-absorption-tomography/stereoscopic-particle-image-velocimetry method directly measures the converted hydrogen (via water vapor) mass flow rate exiting the dual-mode scramjet and compares this to the facility-measured injected hydrogen fuel mass flow rate. A complementary computational fluid dynamics study was performed and results are available for the scram-mode operating condition. The results reported show excellent agreement between the tunable-diode-laser-absorption-tomography/stereoscopic-particle-image-velocimetry-measured combustion efficiency and the computational-fluid-dynamics-predicted combustion efficiency for the scram-mode of operation, which are both near 99%. The tunable-diode-laser-absorption-tomography/stereoscopic-particle-image-velocimetry-measured combustion efficiency for the ram-mode of operation is shown to be lower than that of the scram-mode operation: at 79%.}, number={8}, journal={AIAA JOURNAL}, author={Busa, Kristin M. and Rice, Brian E. and McDaniel, James C. and Goyne, Christopher P. and Rockwell, Robert D. and Fulton, Jesse A. and Edwards, Jack R. and Diskin, Glenn S.}, year={2016}, month={Aug}, pages={2463–2471} }
@article{fulton_edwards_cutler_mcdaniel_goyne_2016, title={Turbulence/chemistry interactions in a ramp-stabilized supersonic hydrogen-air diffusion flame}, volume={174}, ISSN={["1556-2921"]}, DOI={10.1016/j.combustflame.2016.09.017}, abstractNote={Hybrid large-eddy / Reynolds-averaged Navier–Stokes simulations of turbulence / chemistry interactions occurring within a ramp-injected, hydrogen-fueled scramjet combustor are presented in this work. The experimental geometry is one of several studied at the Universty of Virginia as part of the National Center for Hypersonic Combined Cycle Propulsion and consists of an isolator, a combustor, and an extender section. Data collected includes coherent anti-Stokes Raman spectroscopy (CARS) measurements of major species composition and temperature at several streamwise planes, stereoscopic particle image velocimetry (PIV) measurements, hydroxyl planar-induced fluorescence (OH-PLIF) imagery, wall pressure distributions, and line-of-sight profiles of temperature and water concentration obtained using tunable diode laser spectroscopy (TDLAS). This paper focuses on an equivalence ratio of 0.17, which does not produce enough heat release to force a shock train into the isolator. The computational methods utilize a hybrid fourth-order central-difference / upwind strategy to enable accurate resolution of turbulent structures and employ a nine-species hydrogen oxidation mechanism. Generally accurate predictions of temperature, velocity, and nitrogen mole fraction are achieved through a ‘laminar chemistry’ assumption for the filtered species production rates, though results do improve slightly with the use of a simple turbulence / chemistry subgrid closure model. The predictions are most sensitive to the choice of isolator inflow boundary condition, with the use of a recycling / rescaling technique to sustain turbulent fluctuations resulting in an ‘over-mixing’ effect immediately downstream of the fuel injector. Turbulence–chemistry interactions in the flameholding region are examined from the standpoint of laminar flamelet theory. A region of high scalar dissipation rate, coincident with the breakdown of the fuel plume and the interaction of a reflected shock wave with the plume, inhibits flame propagation, forming a ‘hole’ in the flame. Advection of cooler fluid downstream into regions of moderate scalar dissipation enlarges the ‘hole’, but eventually the flame reconnects. These results point to one potential disadvantage of fuel-air mixing technologies that enhance axial vorticity – even if conditions for combustion are favorable, high strain rates generated by the interaction and breakdown of vortex pairs can lead to flame suppression.}, journal={COMBUSTION AND FLAME}, author={Fulton, Jesse A. and Edwards, Jack R. and Cutler, Andrew and McDaniel, Jim and Goyne, Christopher}, year={2016}, month={Dec}, pages={152–165} }
@article{luo_edwards_luo_mueller_2015, title={A fine-grained block ILU scheme on regular structures for GPGPUs}, volume={119}, ISSN={["1879-0747"]}, DOI={10.1016/j.compfluid.2015.07.005}, abstractNote={Iterative methods based on block incomplete LU (BILU) factorization are considered highly effective for solving large-scale block-sparse linear systems resulting from coupled PDE systems with n equations. However, efforts on porting implicit PDE solvers to massively parallel shared-memory heterogeneous architectures, such as general-purpose graphics processing units (GPGPUs), have largely avoided BILU, leaving their enormous performance potential unfulfilled in many applications where the use of implicit schemes and BILU-type preconditioners/solvers is highly preferred. Indeed, strong inherent data dependency and high memory bandwidth demanded by block matrix operations render naive adoptions of existing sequential BILU algorithms extremely inefficient on GPGPUs. In this study, we present a fine-grained BILU (FGBILU) scheme which is particularly effective on GPGPUs. A straightforward one-sweep wavefront ordering is employed to resolve data dependency. Granularity is substantially refined as block matrix operations are carried out in a true element-wise approach. Particularly, the inversion of diagonal blocks, a well-known bottleneck, is accomplished by a parallel in-place Gauss–Jordan elimination. As a result, FGBILU is able to offer low-overhead concurrent computation at O(n2N2) scale on a 3D PDE domain with a linear scale of N. FGBILU has been implemented with both OpenACC and CUDA and tested as a block-sparse linear solver on a structured 3D grid. While FGBILU remains mathematically identical to sequential global BILU, numerical experiments confirm its exceptional performance on an Nvidia GPGPU.}, journal={COMPUTERS & FLUIDS}, author={Luo, Lixiang and Edwards, Jack R. and Luo, Hong and Mueller, Frank}, year={2015}, month={Sep}, pages={149–161} }
@article{potturi_edwards_2015, title={Large-eddy/Reynolds-averaged Navier-Stokes simulation of cavity-stabilized ethylene combustion}, volume={162}, ISSN={["1556-2921"]}, DOI={10.1016/j.combustflame.2014.10.011}, abstractNote={In this study, a hybrid large-eddy/Reynolds-averaged Navier–Stokes (LES/RANS) method is used to simulate ethylene combustion inside a cavity flameholder. The cavity flameholder considered is Configuration E of University of Virginia’s Scramjet Combustion Facility, which consists of a Mach 2 inlet nozzle, a constant-area isolator, a combustor, and an extender, through which the exhaust gases are vented to the atmosphere. To increase the fuel-residence time, a cavity is fitted along the upper wall inside the combustor section of the flameholder. The configuration has the capability of injecting ethylene through a series of ports located upstream of and inside the cavity along the upper wall the combustor. In the simulations, ethylene combustion is modeled using a 22-species ethylene oxidation mechanism. Also, a synthetic eddy method is used to introduce turbulence at the inflow plane of the flameholder. For an equivalence ratio of 0.15, a cavity stabilized flame is predicted. Predictions are compared with line-of-sight temperature, water column-density, water mole-fraction, CO column-density, and CO2 column-density measurements at three stations within and downstream of the cavity. Agreement with experiment is generally good within the cavity. Downstream of the cavity, the simulations predict higher temperatures near the wall. Analysis of the flame structure predicted by the LES/RANS method indicates that the flame propagates into a stoichiometric to fuel-rich mixture near the cavity. Flame angles captured in the simulation are in close agreement with those predicted through classical premixed turbulent flame-speed estimates. Further downstream, the flame structure is non-premixed in character, and near complete conversion of CO to CO2 is observed by the time the flame reaches the combustor exit.}, number={4}, journal={COMBUSTION AND FLAME}, author={Potturi, Amarnatha S. and Edwards, Jack R.}, year={2015}, month={Apr}, pages={1176–1192} }
@article{xia_lou_luo_edwards_mueller_2015, title={OpenACC acceleration of an unstructured CFD solver based on a reconstructed discontinuous Galerkin method for compressible flows}, volume={78}, ISSN={0271-2091}, url={http://dx.doi.org/10.1002/FLD.4009}, DOI={10.1002/FLD.4009}, abstractNote={Summary An OpenACC directive‐based graphics processing unit (GPU) parallel scheme is presented for solving the compressible Navier–Stokes equations on 3D hybrid unstructured grids with a third‐order reconstructed discontinuous Galerkin method. The developed scheme requires the minimum code intrusion and algorithm alteration for upgrading a legacy solver with the GPU computing capability at very little extra effort in programming, which leads to a unified and portable code development strategy. A face coloring algorithm is adopted to eliminate the memory contention because of the threading of internal and boundary face integrals. A number of flow problems are presented to verify the implementation of the developed scheme. Timing measurements were obtained by running the resulting GPU code on one Nvidia Tesla K20c GPU card (Nvidia Corporation, Santa Clara, CA, USA) and compared with those obtained by running the equivalent Message Passing Interface (MPI) parallel CPU code on a compute node (consisting of two AMD Opteron 6128 eight‐core CPUs (Advanced Micro Devices, Inc., Sunnyvale, CA, USA)). Speedup factors of up to 24× and 1.6× for the GPU code were achieved with respect to one and 16 CPU cores, respectively. The numerical results indicate that this OpenACC‐based parallel scheme is an effective and extensible approach to port unstructured high‐order CFD solvers to GPU computing. Copyright © 2015 John Wiley & Sons, Ltd.}, number={3}, journal={International Journal for Numerical Methods in Fluids}, publisher={Wiley}, author={Xia, Yidong and Lou, Jialin and Luo, Hong and Edwards, Jack and Mueller, Frank}, year={2015}, month={Feb}, pages={123–139} }
@article{rockwell_goyne_rice_kouchi_mcdaniel_edwards_2014, title={Collaborative Experimental and Computational Study of a Dual-Mode Scramjet Combustor}, volume={30}, ISSN={["1533-3876"]}, DOI={10.2514/1.b35021}, abstractNote={Advanced computational models of hypersonic air-breathing combustion processes are being developed to better understand and predict the complex flows within a dual-mode scramjet combustor. However, the accuracy of these models can only be quantified through comparison to experimental databases. Moreover, the quality of computational results is dependent on accurate and detailed knowledge of the combustor inflow and boundary conditions. Toward these ends, this paper describes results from a collaboration of experimental and computational investigators. Detailed computational fluid dynamics and finite element analyses were performed throughout the design and implementation of experiments involving a direct-connect scramjet combustor operating at steady state during long duration testing. The test section hardware was designed to provide substantial access for optical laser diagnostics. Measurement locations included the inflow plane and several locations downstream of fuel injection. A suite of advanced in-stream diagnostics were applied, many of which are described in companion papers. Significant results in this paper include measured static wall pressures and temperatures, stereoscopic particle image velocimetry, and focused schlieren imaging. Validated thermal finite element calculations in the scramjet hardware and temperature maps of the flow path boundaries are also presented. Comparison of experimental results with computational fluid dynamics predictions are discussed in a separate paper.}, number={3}, journal={JOURNAL OF PROPULSION AND POWER}, author={Rockwell, Robert D., Jr. and Goyne, Christopher R. and Rice, Brian E. and Kouchi, Toshinori and McDaniel, James C. and Edwards, Jack R.}, year={2014}, pages={530–538} }
@article{ramesh_gopalarathnam_granlund_ol_edwards_2014, title={Discrete-vortex method with novel shedding criterion for unsteady aerofoil flows with intermittent leading-edge vortex shedding}, volume={751}, ISSN={0022-1120 1469-7645}, url={http://dx.doi.org/10.1017/jfm.2014.297}, DOI={10.1017/jfm.2014.297}, abstractNote={Abstract Unsteady aerofoil flows are often characterized by leading-edge vortex (LEV) shedding. While experiments and high-order computations have contributed to our understanding of these flows, fast low-order methods are needed for engineering tasks. Classical unsteady aerofoil theories are limited to small amplitudes and attached leading-edge flows. Discrete-vortex methods that model vortex shedding from leading edges assume continuous shedding, valid only for sharp leading edges, or shedding governed by ad-hoc criteria such as a critical angle of attack, valid only for a restricted set of kinematics. We present a criterion for intermittent vortex shedding from rounded leading edges that is governed by a maximum allowable leading-edge suction. We show that, when using unsteady thin aerofoil theory, this leading-edge suction parameter (LESP) is related to the $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}A_0$ term in the Fourier series representing the chordwise variation of bound vorticity. Furthermore, for any aerofoil and Reynolds number, there is a critical value of the LESP, which is independent of the motion kinematics. When the instantaneous LESP value exceeds the critical value, vortex shedding occurs at the leading edge. We have augmented a discrete-time, arbitrary-motion, unsteady thin aerofoil theory with discrete-vortex shedding from the leading edge governed by the instantaneous LESP. Thus, the use of a single empirical parameter, the critical-LESP value, allows us to determine the onset, growth, and termination of LEVs. We show, by comparison with experimental and computational results for several aerofoils, motions and Reynolds numbers, that this computationally inexpensive method is successful in predicting the complex flows and forces resulting from intermittent LEV shedding, thus validating the LESP concept.}, journal={Journal of Fluid Mechanics}, publisher={Cambridge University Press (CUP)}, author={Ramesh, Kiran and Gopalarathnam, Ashok and Granlund, Kenneth and Ol, Michael V. and Edwards, Jack R.}, year={2014}, month={Jun}, pages={500–538} }
@article{potturi_edwards_2014, title={Hybrid Large-Eddy/Reynolds-Averaged Navier-Stokes Simulations of Flow Through a Model Scramjet}, volume={52}, ISSN={["1533-385X"]}, DOI={10.2514/1.j052595}, abstractNote={The reactive flow through a model scramjet combustor is simulated using a hybrid large-eddy/Reynolds-averaged Navier–Stokes technique. The scramjet configuration considered is similar to the one investigated at the Institute for Chemical Propulsion of the DLR, German Aerospace Center. The model scramjet consists of 15 fuel-injecting holes, located on the base of a wedge-shaped fuel injector, through which hydrogen is injected at sonic conditions. In the present study, only five of the 15 fuel-injecting holes are considered, and periodicity is assumed in the spanwise direction. Several parametric studies are conducted with a view toward determining the sensitivities of the predictions to modeling and algorithmic variations. Different grids (two different topologies), flux reconstruction methods (total variation diminishing and piecewise parabolic method), reaction mechanisms, and inflow boundary conditions (uniform and nonuniform) are used. To enhance fuel–air mixing, a synthetic eddy method is used to generate turbulence in the injector boundary layers and the hydrogen jets. Finally, a partially stirred reactor-type subgrid combustion model is used as a subgrid closure for the species production rates. The results show that, in all the cases, a lifted flame is predicted with varying standoff distances, heat releases, and shapes.}, number={7}, journal={AIAA JOURNAL}, author={Potturi, Amarnatha S. and Edwards, Jack R.}, year={2014}, month={Jul}, pages={1417–1429} }
@article{zilberter_edwards_2014, title={Large-Eddy Simulation/Reynolds-Averaged Navier-Stokes Simulations of High-Speed Mixing Processes}, volume={52}, ISSN={["1533-385X"]}, DOI={10.2514/1.j052745}, abstractNote={A large-eddy simulation/Reynolds-averaged Navier–Stokes model is applied to three high-speed mixing layers and three sonic injection flows to generate data suitable for evaluating two current Reynolds-averaged Navier–Stokes models for turbulent mass diffusivity. These models solve transport equations for concentration variance and dissipation rate and differ in the constitutive relation for the turbulent mass diffusivity and the form of the evolution equation for the dissipation rate. The predictive capability of the large-eddy simulation/Reynolds-averaged Navier–Stokes model is assessed through simulations of an air–air mixing-layer experiment and a sonic ethylene injection into a Mach 2.0 airstream. This model provides good predictions of the mean velocity, turbulence intensity, and rms temperature fluctuation throughout the shear layer flowfield but slightly over-predicts the spreading rate of the mixing layer. The simulation of the sonic injection is in generally good agreement with the experiment but underpredicts the level of jet entrainment. Four other large-eddy simulation/Reynolds-averaged Navier–Stokes data sets, involving the replacement of the lower airstream in the mixing-layer configuration by an argon stream and a helium stream, and a replacement of the injectant gas in the sonic injection experiment with argon and helium are also generated. All data sets are “mined” to extract turbulent mass diffusivities, concentration variances, and scalar dissipation rates associated with the resolved eddy motion. The results show that both models can be optimized to achieve a good match with the exact scalar variance production rate.}, number={7}, journal={AIAA JOURNAL}, author={Zilberter, Ilya A. and Edwards, Jack R.}, year={2014}, month={Jul}, pages={1486–1501} }
@article{fulton_edwards_hassan_mcdaniel_goyne_rockwell_cutler_johansen_danehy_2014, title={Large-Eddy/Reynolds-Averaged Navier-Stokes Simulations of Reactive Flow in Dual-Mode Scramjet Combustor}, volume={30}, ISSN={["1533-3876"]}, DOI={10.2514/1.b34929}, abstractNote={Numerical simulations of the turbulent reactive flow within a model scramjet combustor configuration, experimentally mapped at the University of Virginia’s Scramjet Combustion Facility at an equivalence ratio of 0.17, are described in this paper. A hybrid large-eddy simulation/Reynolds-averaged Navier–Stokes method is used, with special attention focused on capturing facility-specific effects, such as asymmetric inflow temperature distributions, on flow development within the combustor. Predictions obtained using two nine-species hydrogen oxidation models are compared with experimental data obtained using coherent anti-Stokes Raman spectroscopy, hydroxyl radical planar laser-induced fluorescence, stereoscopic particle image velocimetry, and focusing schlieren techniques. The large-eddy simulation/Reynolds-averaged Navier–Stokes models accurately capture the mean structure of the fully developed flame but tend to overpredict fluctuation levels toward the outer edge of the reactive plume. Model predictions worsen in the flame-anchoring region just downstream of the fuel injector. Here, turbulence/chemistry interactions are more pronounced, and the flame is more influenced by the inflow conditions. Comparisons with hydroxyl radical planar laser-induced fluorescence imagery indicate that the large-eddy simulation/Reynolds-averaged Navier–Stokes model can capture the effects of larger turbulent scales in deforming the flame structure but does not capture the effects of small turbulent structures in broadening the OH profiles.}, number={3}, journal={JOURNAL OF PROPULSION AND POWER}, author={Fulton, Jesse A. and Edwards, Jack R. and Hassan, Hassan A. and McDaniel, James C. and Goyne, Christopher P. and Rockwell, Robert D. and Cutler, Andrew D. and Johansen, Craig T. and Danehy, Paul M.}, year={2014}, pages={558–575} }
@article{salazar_edwards_2014, title={Mach 6 Wake Flow Simulations Using a Large-Eddy Simulation/Reynolds-Averaged Navier Stokes Model}, volume={51}, ISSN={["1533-6794"]}, DOI={10.2514/1.a32729}, abstractNote={A hybrid large-eddy simulation/Reynolds-averaged Navier–Stokes turbulence model is used to simulate the Mach 6 flow around a scaled model similar to NASA’s Orion multipurpose crew vehicle. The results for surface pressure and heat transfer are compared with experimental data from previous base flow experiments conducted at the Calspan—University at Buffalo Research Center. Using the highest Reynolds number test case ( based on capsule diameter), different numerical aspects of the hybrid approach are addressed, such as use of a low-dissipation scheme, a modification to the eddy-viscosity blending function, time-averaging results, filtering computational results, and sensitivity to grid resolution. In addition, results are compared with Reynolds-Averaged Navier–Stokes using Menter’s two-equation baseline model and to detached-eddy simulation predictions. By introducing a new modification to the blending from Reynolds-averaged Navier–Stokes to large-eddy simulation within boundary layers, very good agreement with the experiment is obtained in regions where the boundary-layer grid spacing is too coarse for large-eddy simulation. The findings show that the high-fidelity schemes produce results that agree much better with the experimental data than Reynolds-averaged Navier–Stokes methods, which tend to underpredict base pressures and overpredict heat fluxes. The overall accuracy of each scheme is evaluated using a normalized root mean square error in different regions of the flow, and the analysis shows that, in separated regions, the integrated error is over 120% using a Reynolds-averaged Navier–Stokes model, and 30–50% using the higher fidelity schemes. Additionally, the hybrid methodology presented is further validated by considering a lower Reynolds number , where the flow is nominally transitional, and very accurate heat transfer predictions are also obtained.}, number={4}, journal={JOURNAL OF SPACECRAFT AND ROCKETS}, author={Salazar, Giovanni and Edwards, Jack R.}, year={2014}, pages={1329–1348} }
@article{ramesh_gopalarathnam_edwards_ol_granlund_2013, title={An unsteady airfoil theory applied to pitching motions validated against experiment and computation}, volume={27}, ISSN={0935-4964 1432-2250}, url={http://dx.doi.org/10.1007/s00162-012-0292-8}, DOI={10.1007/s00162-012-0292-8}, number={6}, journal={Theoretical and Computational Fluid Dynamics}, publisher={Springer Science and Business Media LLC}, author={Ramesh, Kiran and Gopalarathnam, Ashok and Edwards, Jack R. and Ol, Michael V. and Granlund, Kenneth}, year={2013}, month={Jan}, pages={843–864} }
@article{niu_edwards_2012, title={A simple incompressible flux splitting for sharp free surface capturing}, volume={69}, ISSN={["1097-0363"]}, DOI={10.1002/fld.2658}, abstractNote={SUMMARY This paper first applies a flux vector‐type splitting method based on the numerical speed of sound for computing incompressible single and multifluid flows. Here, a preconditioning matrix based on Chorin's artificial compressibility concept is used to modify the incompressible multifluid Navier–Stokes equations to be hyperbolic and density or volume fraction‐independent. The current approach can reduce eigenvalues disparity induced from density or volume fraction ratios and enhance numerical stability. Also, a simple convection‐pressure flux‐splitting method with high‐order essentially nonoscillatory‐type primitive variable extrapolations coupled with monotone upstream‐centered schemes for conservation laws‐type volume fraction recompressed reconstruction is used to maintain the preservation of sharp interface evolutions in multifluid flow simulations. Benchmark tests including a solid rotation test of a notched two‐dimensional cylinder, the evolution of spiral and rotational shapes of deformable circles, a dam breaking problem, and the Rayleigh–Taylor instability were chosen to validate the current incompressible multifluid methodology. An incompressible driven cavity was also chosen to check the robustness of the proposed method on the computation of single fluid incompressible flow problems. Copyright © 2011 John Wiley & Sons, Ltd.}, number={10}, journal={INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS}, author={Niu, Yang-Yao and Edwards, Jack R.}, year={2012}, month={Aug}, pages={1661–1678} }
@article{choi_edwards_rosati_eisner_2012, title={Large Eddy Simulation of Particle Re-suspension During a Footstep}, volume={46}, ISSN={["1521-7388"]}, DOI={10.1080/02786826.2011.631613}, abstractNote={Re-suspension of particulate matter under human activity can have a significant impact on particle concentrations in indoor environments. The removal of surface-bound particulates as a person's foot contacts a substrate and the subsequent transport of such particulates through wake entrainment effects and through deposition is an important mechanism for particle dispersion. To study aspects of this event, we perform high-fidelity simulations of particle transport due to the heel-to-toe contact of a foot with a particle-laden carpet. For this purpose, an immersed boundary method is extended to account for particle transport, re-suspension, and deposition near the surface of the foot. Particle deposition is modeled as a combination of gravitational settling, Brownian diffusion, and convective impaction, while a dynamic re-suspension model is used to model particle re-suspension from the surfaces. We demonstrate the details of transient transport phenomena of re-suspended particles during a heel-to-toe foot motion event. The effects of the thickness of the carpet layer, the foot penetration depth into the carpet layer, the foot speed, and particle sizes on the mass re-suspended are investigated. Parametric studies show that a deeper foot penetration into a thinner carpet layer increases particle re-suspension and a faster foot motion also increases the re-suspension. Re-suspension rates increase as the particle size increases for particles in a size range of 1–20 μm. Predicted re-suspension rates are compared with those obtained in recent experiments. Copyright 2012 American Association for Aerosol Research}, number={7}, journal={AEROSOL SCIENCE AND TECHNOLOGY}, author={Choi, Jung-Il and Edwards, Jack R. and Rosati, Jacky A. and Eisner, Alfred D.}, year={2012}, pages={767–780} }
@article{choi_edwards_2012, title={Large-eddy simulation of human-induced contaminant transport in room compartments}, volume={22}, ISSN={["0905-6947"]}, DOI={10.1111/j.1600-0668.2011.00741.x}, abstractNote={A large-eddy simulation is used to investigate contaminant transport owing to complex human and door motions and vent-system activity in room compartments where a contaminated and clean room are connected by a vestibule. Human and door motions are simulated with an immersed boundary procedure. We demonstrate the details of contaminant transport owing to human- and door-motion-induced wake development during a short-duration event involving the movement of a person (or persons) from a contaminated room, through a vestibule, into a clean room. Parametric studies that capture the effects of human walking pattern, door operation, over-pressure level, and vestibule size are systematically conducted. A faster walking speed results in less mass transport from the contaminated room into the clean room. The net effect of increasing the volume of the vestibule is to reduce the contaminant transport. The results show that swinging-door motion is the dominant transport mechanism and that human-induced wake motion enhances compartment-to-compartment transport.The effect of human activity on contaminant transport may be important in design and operation of clean or isolation rooms in chemical or pharmaceutical industries and intensive care units for airborne infectious disease control in a hospital. The present simulations demonstrate details of contaminant transport in such indoor environments during human motion events and show that simulation-based sensitivity analysis can be utilized for the diagnosis of contaminant infiltration and for better environmental protection.}, number={1}, journal={INDOOR AIR}, author={Choi, J. -I. and Edwards, J. R.}, year={2012}, month={Feb}, pages={77–87} }
@article{edwards_boles_baurle_2012, title={Large-eddy/Reynolds-averaged Navier-Stokes simulation of a supersonic reacting wall jet}, volume={159}, ISSN={["1556-2921"]}, DOI={10.1016/j.combustflame.2011.10.009}, abstractNote={This work presents results from large-eddy/Reynolds-averaged Navier–Stokes (LES/RANS) simulations of the well-known Burrows–Kurkov supersonic reacting wall-jet experiment. Generally good agreement with experimental mole fraction, stagnation temperature, and Pitot pressure profiles is obtained for non-reactive mixing of the hydrogen jet with a non-vitiated air stream. A lifted flame, stabilized between 15 and 20 cm downstream of the hydrogen jet, is formed for hydrogen injected into a vitiated air stream. Flame stabilization occurs closer to the hydrogen injection location when a three-dimensional combustor geometry (with boundary layer development resolved on all walls) is considered. Volumetric expansion of the reactive shear layer is accompanied by the formation of large eddies which interact strongly with the reaction zone. Time averaged predictions of the reaction zone structure show an under-prediction of the peak water concentration and stagnation temperature, relative to experimental data, but display generally good agreement with the extent of the reaction zone. Reactive scalar scatter plots indicate that the flame exhibits a transition from a partially-premixed flame structure, characterized by intermittent heat release, to a diffusion-flame structure that could probably be described by a strained laminar flamelet model.}, number={3}, journal={COMBUSTION AND FLAME}, author={Edwards, Jack R. and Boles, John A. and Baurle, Robert A.}, year={2012}, month={Mar}, pages={1127–1138} }
@article{ghosh_edwards_choi_2012, title={Numerical Simulation of Effects of Mesoflaps in Controlling Shock/Boundary-Layer Interactions}, volume={28}, ISSN={["0748-4658"]}, DOI={10.2514/1.b34297}, abstractNote={This work utilizes an immersed-boundary method to simulate the effects of an array of aeroelastic mesoflaps in controlling oblique shock/turbulent boundary-layer interactions. A loosely coupled approach is adopted for the fluid-structure interaction problem, with separate solvers used for the fluid and structural domains. The mesoflaps are rendered as immersed objects for the fluid solver and modeled as cantilevered Euler-Bernoulli beams for the structural solver. Determination of the aerodynamic loads acting on the mesoflap surfaces from the surrounding fluid is done using a nearest neighbor approach combined with a bi-linear interpolation scheme. Simulations are performed for a Mach 2.46 shock / boundary layer interaction with and without control, based on experiments conducted at University of Illinois at Urbana-Champaign. Both Reynolds-averaged Navier-Stokes (RANS) and hybrid large-eddy/Reynolds-averaged Navier-Stokes (LES/RANS) turbulence closures are used. For the computations of the flow with mesoflap control, both 2-D quasi-steady and 3-D dynamic simulations of the fluid-structure interaction problem are performed. Comparisons made with experimental laser Doppler anemometry data and wall pressure measurements for flows with and without control show reasonable agreement, with better predictions away from the separation region. An analysis of the flow indicates that the mesoflap control system does not eliminate axial flow separation. Also, analysis of the frequency content of the mesoflap deflections suggests that a correlation might exist between the dominant frequency of the flap deflection and the low-frequency shock motion observed in separated flows.}, number={5}, journal={JOURNAL OF PROPULSION AND POWER}, author={Ghosh, Santanu and Edwards, Jack R. and Choi, Jung-Il}, year={2012}, pages={955–970} }
@article{gieseking_edwards_2012, title={Study of a Compression-Ramp Interaction Using Large-Eddy Simulation/Reynolds-Averaged Navier-Stokes Models}, volume={50}, ISSN={["1533-385X"]}, DOI={10.2514/1.j051195}, abstractNote={Two large-eddy simulation/Reynolds-averaged Navier–Stokes models are applied to a shock/boundary interaction generated by a 20 deg compression corner. The models are designed to transition from unsteady Reynolds-averaged Navier–Stokes to large-eddy simulation as the boundary layer shifts from its logarithmic behavior to its wakelike response, but they differ in that one model requires a preselection of a model constant for each problem, while the other computes this constant as a function of local and ensemble-averaged turbulence properties. Predictions are compared with mean-flow and second-moment experimental data obtained at Princeton University. In general, calculatedmean-flow velocity, surface-pressure, and surface skin-friction distributions agree well with the experiment, with the most noticeable discrepancy being a slight overprediction of the level of upstream influence induced by the shock wave. Comparisons with mass-flux fluctuation intensity, Reynolds axial stress, and Reynolds shear-stress profiles are also presented. These show generally good agreement with experimental trends relating to Reynolds stress amplification and anisotropy modulation. The calculations also predict the existence of a low-frequency motion of the separation shock that is probably associated with the motion of the backflow region. Higher-frequency modulations of the shock front as induced by the passage of coherent, streaklike structures through the shock also appear to contribute to the measurable intermittency effects.}, number={10}, journal={AIAA JOURNAL}, author={Gieseking, Daniel A. and Edwards, Jack R.}, year={2012}, month={Oct}, pages={2057–2068} }
@article{gieseking_choi_edwards_hassan_2011, title={Compressible-Flow Simulations Using a New Large-Eddy Simulation/Reynolds-Averaged Navier-Stokes Model}, volume={49}, ISSN={["1533-385X"]}, DOI={10.2514/1.j051001}, abstractNote={A new hybrid large-eddy simulation/Reynolds-averaged Navier–Stokes simulation (LES/RANS) method is presented in this work. In this approach, the resolved turbulence kinetic energy, ensemble-averaged modeled turbulence kinetic energy and turbulence frequency, and time-resolved turbulence frequency are used to form an estimate of an outer-layer turbulence length scale that is nearly Reynolds-number-independent. The ratio of this outer-layer scale with an inner-layer length scale (proportional to the wall distance) is used to construct a blending function that facilitates the shift between an unsteady RANS formulation near solid surfaces and a LES formulation away from the wall. The new model is tested through simulations of compressible flat-plate boundary layers over a widerangeofReynoldsnumbersandMach2.86 flowoverasmoothcompressionramp.Theresultsshowthatthenew modelpredicts mean andsecond-moment statistics that arein goodagreement withexperiment andare comparable with those obtained using an earlier model (Edwards, J. R., Choi, J-I., and Boles, J. A., “Hybrid Large-Eddy/ Reynolds-Averaged Navier–Stokes Simulation of a Mach-5 Compression Corner Interaction,” AIAA Journal, Vol. 464, 2008, pp. 977–991.) which required a case-by-case calibration of a model constant.}, number={10}, journal={AIAA JOURNAL}, author={Gieseking, Daniel A. and Choi, Jung-Il and Edwards, Jack R. and Hassan, Hassan A.}, year={2011}, month={Oct}, pages={2194–2209} }
@article{robichaud_dixon_potturi_cassidy_edwards_sohn_dow_muddiman_2011, title={Design, modeling, fabrication, and evaluation of the air amplifier for improved detection of biomolecules by electrospray ionization mass spectrometry}, volume={300}, ISSN={["1873-2798"]}, DOI={10.1016/j.ijms.2010.04.006}, abstractNote={Through a multi-disciplinary approach, the air amplifier is being evolved as a highly engineered device to improve detection limits of biomolecules when using electrospray ionization. Several key aspects have driven the modifications to the device through experimentation and simulations. We have developed a computer simulation that accurately portrays actual conditions and the results from these simulations are corroborated by the experimental data. These computer simulations can be used to predict outcomes from future designs resulting in a design process that is efficient in terms of financial cost and time. We have fabricated a new device with annular gap control over a range of 50 to 70 μm using piezoelectric actuators. This has enabled us to obtain better aerodynamic performance when compared to the previous design (2× more vacuum) and also more reproducible results. This is allowing us to study a broader experimental space than the previous design which is critical in guiding future directions. This work also presents and explains the principles behind a fractional factorial design of experiments methodology for testing a large number of experimental parameters in an orderly and efficient manner to understand and optimize the critical parameters that lead to obtain improved detection limits while minimizing the number of experiments performed. Preliminary results showed that several folds of improvements could be obtained for certain condition of operations (up to 34 folds).}, number={2-3}, journal={INTERNATIONAL JOURNAL OF MASS SPECTROMETRY}, author={Robichaud, Guillaume and Dixon, R. Brent and Potturi, Amarnatha S. and Cassidy, Dan and Edwards, Jack R. and Sohn, Alex and Dow, Thomas A. and Muddiman, David C.}, year={2011}, month={Mar}, pages={99–107} }
@article{mcgowan_granlund_ol_gopalarathnam_edwards_2011, title={Investigations of Lift-Based Pitch-Plunge Equivalence for Airfoils at Low Reynolds Numbers}, volume={49}, ISSN={["0001-1452"]}, DOI={10.2514/1.j050924}, abstractNote={The limits of linear superposition in two-dimensional high-rate low-Reynolds-number aerodynamics are examined by comparing the lift-coefficient history and flowfield evolution for airfoils undergoing harmonic motions in pure pitch, pure plunge, and pitch―plunge combinations. Using quasi-steady airfoil theory and Theodorsen's formula as predictive tools, pitching motions are sought that produce lift histories identical to those of prescribed plunging motions. It follows that a suitable phasing of pitch and plunge in a combined motion should identically produce zero lift, canceling either the circulatory contribution (with quasi-steady theory) or the combination of circulatory and noncirculatory contributions (with Theodorsen's formula). Lift history is measured experimentally in a water tunnel using a force balance and is compared with two-dimensional Reynolds-averaged Navier―Stokes computations and Theodorsen's theory; computed vorticity contours are compared with dye injection in the water tunnel. Theodorsen's method evinces considerable, and perhaps surprising, resilience in finding pitch-to-plunge equivalence of lift-coefficient―time history, despite its present application to cases in which its mathematical assumptions are demonstrably violated. A combination of pitch and plunge motions can be found such that net lift coefficient is nearly identically zero for arbitrarily high reduced frequency, provided that amplitude is small. Conversely, cancellation is possible at large motion amplitude, provided that reduced frequency is moderate. The product of Strouhal number and nondimensional amplitude is therefore suggested as the upper bound for when superposition and linear predictions remain valid in massively unsteady two-dimensional problems.}, number={7}, journal={AIAA JOURNAL}, author={McGowan, Gregory Z. and Granlund, Kenneth and Ol, Michael V. and Gopalarathnam, Ashok and Edwards, Jack R.}, year={2011}, month={Jul}, pages={1511–1524} }
@article{oberoi_choi_edwards_rosati_thornburg_rodes_2010, title={Human-Induced Particle Re-Suspension in a Room}, volume={44}, ISSN={["1521-7388"]}, DOI={10.1080/02786820903530852}, abstractNote={A large-eddy simulation/immersed boundary method for particulate flows in an Eulerian framework is utilized to investigate short-term particle re-suspension due to human motion. The simulations involve a human walking through a room, stopping, and then walking in place, causing particles to be re-suspended from a carpet. The carpet layer is modeled as the porous medium and a classical adhesive force model is applied to model the resistance of the carpet-bound material to hydrodynamic forcing. The effects of parameters such as the foot penetration depth and adhesive force coefficient on mass re-suspended during the foot stamping events are examined. Simulations of particulate re-suspension experiments conducted in a room within a U.S. Environmental Protection Agency test house are also described. The simulations vary the type of human motion (stamping in place versus stamping in place with rotation). The results indicate that significant amounts of particulate material are re-suspended from the carpet layer due to the impingement of the feet during the motion event. The net mass re-suspended for human motion with rotation is two times greater than that for the motion without rotation, while the mass of re-suspended small particles is slightly greater than that of large particles. The re-suspension rates are estimated based on several time scales, and the predicted total particle number concentrations at several locations in the room show good agreement with experimental data. The present CFD model can be utilized to predict particle re-suspension rates as induced by human motion, but further work in modeling the fine-scale details of the re-suspension process is needed.}, number={3}, journal={AEROSOL SCIENCE AND TECHNOLOGY}, author={Oberoi, Roshan C. and Choi, Jung-Il and Edwards, Jack R. and Rosati, Jacky A. and Thornburg, Jonathan and Rodes, Charles E.}, year={2010}, pages={216–229} }
@article{baurle_edwards_2010, title={Hybrid Reynolds-Averaged/Large-Eddy Simulations of a Coaxial Supersonic Freejet Experiment}, volume={48}, ISSN={["0001-1452"]}, DOI={10.2514/1.43771}, abstractNote={Reynolds-averaged and hybrid Reynolds-averaged/large-eddy simulations have been applied to a supersonic coaxial jet flow experiment. The experiment was designed to study compressible mixing flow phenomenon under conditions that are representative of those encountered in scramjet combustors. The experiment used either helium or argon as the inner jet nozzle fluid, and the outer jet nozzle fluid consisted of laboratory air. The inner and outer nozzles were designed and operated to produce nearly pressure-matched Mach 1.8 flow conditions at the jet exit. The purpose of the computational effort was to assess the state of the art for each modeling approach and to use the hybrid Reynolds-averaged/large-eddy simulations to gather insight into the deficiencies of the Reynolds-averaged closure models. The Reynolds-averaged simulations displayed a strong sensitivity to choice of turbulent Schmidt number. The initial value chosen for this parameter resulted in an overprediction of the mixing layer spreading rate for the helium case, but the opposite trend was observed when argon was used as the injectant. A larger turbulent Schmidt number greatly improved the comparison of the results with measurements for the helium simulations, but variations in the Schmidt number did not improve the argon comparisons. The hybrid Reynolds-averaged/largeeddy simulations also overpredicted the mixing layer spreading rate for the helium case, while underpredicting the rate of mixing when argon was used as the injectant. The primary reason conjectured for the discrepancy between the hybrid simulation results and the measurements centered around issues related to the transition from a Reynolds-averaged state to one with resolved turbulent content. Improvements to the inflow conditions were suggested as a remedy to this dilemma. Second-order turbulence statistics were also compared with their modeled Reynolds-averaged counterparts to evaluate the effectiveness of common turbulence closure assumptions.}, number={3}, journal={AIAA JOURNAL}, author={Baurle, R. A. and Edwards, J. R.}, year={2010}, month={Mar}, pages={551–571} }
@article{boles_edwards_baurle_2010, title={Large-Eddy/Reynolds-Averaged Navier-Stokes Simulations of Sonic Injection into Mach 2 Crossflow}, volume={48}, ISSN={["1533-385X"]}, DOI={10.2514/1.j050066}, abstractNote={Computational predictions of transverse injection of air, helium, and ethylene into a Mach 1.98 crossflow of air are presented. A hybrid large-eddy simulation/Reynolds-averaged Navier―Stokes turbulence model is used. A blending function, dependent on modeled turbulence variables, is used to shift the turbulence closure from the Menter t-ω model near solid surfaces to a Smagorinsky subgrid model in the outer part of the incoming boundary layer and in the jet mixing zone. The results show reasonably good agreement with time-averaged Mie-scattering images of the plume structure for both helium and air injection and with experimental surface pressure distributions, even though the penetration of the jet into the crossflow is slightly overpredicted. Predictions of ethylene mole fraction at several transverse stations within the plume are in good agreement with time-averaged Raman-scattering mole-fraction data. The model results are used to examine the validity of the commonly used assumption of the constant turbulent Schmidt number in the intense mixing zone downstream of the injection location. The assumption of a constant turbulent Schmidt is shown to be inadequate for jet mixing dominated by large-scale entrainment.}, number={7}, journal={AIAA JOURNAL}, author={Boles, John A. and Edwards, Jack R. and Baurle, Robert A.}, year={2010}, month={Jul}, pages={1444–1456} }
@article{ghosh_choi_edwards_2010, title={Numerical Simulations of Effects of Micro Vortex Generators Using Immersed-Boundary Methods}, volume={48}, ISSN={["0001-1452"]}, DOI={10.2514/1.40049}, abstractNote={This work presents an immersed-boundary technique for compressible, turbulent flows and applies the technique to simulate the effects of micro vortex generators in controlling oblique-shock/turbulent boundary-layer interactions. The Reynolds-averaged Navier-Stokes equations, closed using the Menter k-ω turbulence model, are solved in conjunction with the immersed-boundary technique. The approach is validated by comparing solutions obtained using the immersed-boundary technique with solutions obtained on a body-fitted mesh and with experimental laser Doppler anemometry data collected at Cambridge University for Mach 2.5 flow over single micro vortex generators. Simulations of an impinging oblique-shock boundary-layer interaction at Mach 2.5 with and without micro vortex-generator flow control are also performed, considering the development of the flow in the entire wind tunnel. Comparisons are made with experimental laser Doppler anemometry data and surface-pressure measurements from Cambridge University and an analysis of the flow structure is performed. The results show that three dimensional effects initiated by the interaction of the oblique shock with the sidewall boundary layers significantly influence the flow patterns in the actual experiment. The general features of the interactions with and without the micro vortex-generator array are predicted to good accord by the Reynolds-averaged Navier-Stokes/ immersed-boundary model.}, number={1}, journal={AIAA JOURNAL}, author={Ghosh, Santanu and Choi, Jung-Il and Edwards, Jack R.}, year={2010}, month={Jan}, pages={92–103} }
@article{ghosh_choi_edwards_2010, title={Simulation of Shock/Boundary-Layer Interactions with Bleed Using Immersed-Boundary Methods}, volume={26}, ISSN={["0748-4658"]}, DOI={10.2514/1.45297}, abstractNote={This work utilizes an immersed boundary (IB) method to simulate the effects of arrays of discrete bleed ports in controlling shock wave / turbulent boundary layer inter actions . Both Reynolds averaged Navier -Stokes (RANS) and hybrid large -eddy / Reynolds -averaged Navier -Stokes (LES/RANS) turbulence closures are used with the IB technique. The approach is validated by conducting simulations of Mach 2.5 flow over a perfo rated plate containing 18 individual bleed holes. Predictions of discharge coefficient as a function of bleed plenum pressure are compared with experimental data. Simulations of an impinging oblique shock / boundary layer interaction at Mach 2.45 with an d without active bleed control are also performed. The 68 -hole bleed plate is rendered as an immersed object in the computational domain. Wall pressure predictions show that, in general, the LES/RANS technique under -estimate s the upstream extent of axi al separation that occurs in the absence of bleed. Good agreement with P itot -pressure surveys throughout the interaction region is obtained, however. Active suction completely removes the separation region and induces local disturbances in the wall pres sure distributions that are associated with the expansion of the boundary layer fluid into the bleed port and its subsequ ent re -compression. Predicted Pitot -pressure distributions are in good agreement with experiment for the case with bleed. Swirl stre ngth probability -density distributions are used to estimate the evolution of turbulence length -sca les throughout the interaction, and the effects of bleed on the amplification of Reynolds stresses are highlighted. Finally, simple improvements to engineerin g-level bleed models are proposed based on the computational results.}, number={2}, journal={JOURNAL OF PROPULSION AND POWER}, author={Ghosh, Santanu and Choi, Jung-Il and Edwards, Jack R.}, year={2010}, pages={203–214} }
@article{cassidy_edwards_tian_2009, title={An investigation of interface-sharpening schemes for multi-phase mixture flows}, volume={228}, ISSN={["1090-2716"]}, DOI={10.1016/j.jcp.2009.02.028}, abstractNote={This work evaluates several approaches for sharp phase interface-capturing in computations of multi-phase mixture flows. Attention is focused on algebraic interface-capturing strategies that fit directly within a finite-volume MUSCL-type framework, in which dimension-by-dimension reconstruction of interface states based on extrapolated fluid properties is the norm. In this scope, linear, sine-wave, and tangent hyperbola volume-fraction reconstructions are examined for a range of problems, including advection of a volume-fraction discontinuity, the Rayleigh–Taylor instability, a dam-break problem, an axisymmetric jet instability, the Rayleigh instability, and flow within an aerated-liquid injector. An implicit dual-time stepping approach, applied directly to a preconditioned form of the governing equations, is used for time-advancement. The results show that the sharpening strategies are successful in providing two-to-three-cell capturing of volume-fraction discontinuities.}, number={16}, journal={JOURNAL OF COMPUTATIONAL PHYSICS}, author={Cassidy, Daniel A. and Edwards, Jack R. and Tian, Ming}, year={2009}, month={Sep}, pages={5628–5649} }
@article{choi_edwards_baurle_2009, title={Compressible Boundary-Layer Predictions at High Reynolds Number Using Hybrid LES/RANS Methods}, volume={47}, ISSN={["1533-385X"]}, DOI={10.2514/1.41598}, abstractNote={Simulations of compressible boundary-layer flow at three different Reynolds numbers (Re δ = 5.59 × 10 4 , 1.78 × 10 5 , and 1.58 x 10 6 ) are performed using a hybrid large-eddy simulation/Reynolds-averaged Navier-Stokes method. Variations in the recycling/rescaling method, the higher order extension, the choice of primitive variables, the Reynolds-averaged Navier-Stokes to large eddy simulation transition parameters, and the mesh resolution are considered in order to assess the model. The results indicate that the present model can provide good predictions of the mean-flow properties, second-moment statistics, and structural features of the boundary layers considered. Normalized turbulent statistics in the outer layer are found to be independent of Reynolds number, similar to incompressible turbulent boundary layers.}, number={9}, journal={AIAA JOURNAL}, author={Choi, Jung-Il and Edwards, Jack R. and Baurle, Robert A.}, year={2009}, month={Sep}, pages={2179–2193} }
@article{choi_edwards_2008, title={Large eddy simulation and zonal modeling of human-induced contaminant transport}, volume={18}, ISSN={["1600-0668"]}, DOI={10.1111/j.1600-0668.2008.00527.x}, abstractNote={An immersed boundary method for particulate flow in an Eulerian framework is utilized to examine the effects of complex human motion on the transport of trace contaminants. The moving human object is rendered as a level set in the computational domain, and realistic human walking motion is implemented using a human kinematics model. A large eddy simulation (LES) technique is used to simulate the fluid and particle dynamics induced by human activity. Parametric studies are conducted within a Room-Room and a Room-Hall configuration, each separated by an open doorway. The effects of the average walking speed, initial proximity from the doorway, and the initial mass loading on room-to-room contaminant transport are examined. The rate of mass transport increases as the walking speed increases, but the total amount of material transported is more influenced by the initial proximity of the human from the doorway. The Room-Hall simulations show that the human wake transports material over a distance of about 8 m. Time-dependent data extracted from the simulations is used to develop a room-averaged zonal model for contaminant transport due to human walking motion. The model shows good agreement with the LES results.The effect of human activity on contaminant transport may be important in applications such as clean or isolation room design for biochemical production lines, in airborne infection control, and in entry/exit into collective protection or decontamination systems. The large eddy simulations (LES) performed in this work allow precise capturing of the local wakes generated by time-dependent human motion and thus provide a means of quantifying contaminant transport due to wake effects. The LES database can be used to develop zonal models for the bulk effects of human-induced contaminant transport. These may be incorporated into multi-zone infiltration models for use in threat-response and exposure mitigation studies.}, number={3}, journal={INDOOR AIR}, author={Choi, J. -I. and Edwards, J. R.}, year={2008}, month={Jun}, pages={233–249} }
@article{edwards_choi_boles_2008, title={Large-eddy/Reynolds-averaged Navier-Stokes simulation of a Mach 5 compression-corner interaction}, volume={46}, ISSN={["1533-385X"]}, DOI={10.2514/1.32240}, abstractNote={Simulations of Mach 5 turbulent flow over a 28-deg compression corner are performed using a hybrid large-eddy/ Reynolds-averaged Navier-Stokes method. The model captures the mean-flow structure of the interaction reasonably well, with observed deficiencies relating to an underprediction of the displacement effects of the shock-induced separation region. The computational results provide some support for a recent theory concerning the underlying causes of low-frequency shock-wave oscillation. In the simulations, the sustained presence of a collection of streaks of fluid with lower/higher momentum than the average induces a low-frequency undulation of the separation front. Power spectra obtained at different streamwise stations are in good agreement with experimental results. Downstream of reattachment, the simulations capture a three-dimensional mean-flow structure, dominated by counter-rotating vortices that produce wide variations in the surface skin friction. Predictions of the structure of the reattaching boundary layer agree well with experimental pitot pressure measurements. In comparison with Reynolds-averaged model predictions, the hybrid large-eddy/Reynolds-averaged Navier-Stokes model predicts more amplification of the Reynolds stresses and a broadening of the Reynolds stress distribution within the boundary layer that is probably due to reattachment-shock motion.}, number={4}, journal={AIAA JOURNAL}, author={Edwards, Jack R. and Choi, Jung-Il and Boles, John A.}, year={2008}, month={Apr}, pages={977–991} }
@article{edwards_2008, title={Numerical simulations of shock/boundary layer interactions using time-dependent modeling techniques: A survey of recent results}, volume={44}, ISSN={["0376-0421"]}, DOI={10.1016/j.paerosci.2008.06.004}, abstractNote={Supersonic or hypersonic flows within and around flight vehicles inevitably involve interactions of strong shock waves with boundary layers. Flows within inlet/isolator configurations, and flows induced by control surface deflections are some examples. Such interactions are time dependent in nature and are often subject to low-frequency, large-scale motion that induces local pressure and heating loads. With recent increases in available computer power, it has now become possible to simulate such interactions at experimentally relevant Reynolds numbers using time-dependent techniques, such as direct numerical simulation (DNS), large-eddy simulation (LES), and hybrid large-eddy simulation/Reynolds-averaged Navier–Stokes (LES–RANS) methods. This paper will survey some recent work in this area and will describe insights in shock/boundary layer interaction physics gained by using these high-fidelity methods. Attention will be focused on studies that compare directly with experimental data at the same (or nearly the same) Reynolds number. Challenges in the application of these techniques to even more complicated high-speed flow fields are also outlined.}, number={6}, journal={PROGRESS IN AEROSPACE SCIENCES}, author={Edwards, Jack R.}, year={2008}, month={Aug}, pages={447–465} }
@article{amar_blackwell_edwards_2008, title={One-dimensional ablation using a full Newton's method and finite control volume procedure}, volume={22}, ISSN={["0887-8722"]}, DOI={10.2514/1.29610}, abstractNote={The development and verification of a one-dimensional constant density material thermal response code with ablation is presented. The implicit time integrator, control volume finite element spatial discretization, and Newton's method (with an analytical Jacobian) for the entire system of residual equations have been implemented and verified for variable material properties, Q* ablation, and thermochemical ablation problems. Timing studies were performed, and when accuracy is considered, the method developed in this study exhibits significant time savings over the property lagging approach. In addition, maximizing the Newton solver's convergence rate by including sensitivities to the surface recession rate reduces the overall computational time when compared to excluding recession rate sensitivities.}, number={1}, journal={JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER}, author={Amar, A. J. and Blackwell, B. F. and Edwards, J. R.}, year={2008}, pages={71–82} }
@article{choi_oberoi_edwards_rosati_2007, title={An immersed boundary method for complex incompressible flows}, volume={224}, ISSN={["1090-2716"]}, DOI={10.1016/j.jcp.2006.10.032}, abstractNote={An immersed boundary method for time-dependent, three-dimensional, incompressible flows is presented in this paper. The incompressible Navier–Stokes equations are discretized using a low-diffusion flux splitting method for the inviscid fluxes and second-order central-differences for the viscous components. Higher-order accuracy achieved by using weighted essentially non-oscillatory (WENO) or total variation diminishing (TVD) schemes. An implicit method based on artificial compressibility and dual-time stepping is used for time advancement. The immersed boundary surfaces are defined as clouds of points, which may be structured or unstructured. Immersed-boundary objects are rendered as level sets in the computational domain, and concepts from computational geometry are used to classify points as being outside, near, or inside the immersed boundary. The velocity field near an immersed surface is determined from separate interpolations of the components tangent and normal to the surface. The tangential velocity near the surface is constructed as a power-law function of the local wall normal distance. Appropriate choices of the power law enable the method to approximate the energizing effects of a turbulent boundary layer for higher Reynolds number flows. Five different flow problems (flow over a circular cylinder, an in-line oscillating cylinder, a NACA0012 airfoil, a sphere, and a stationary mannequin) are simulated using the present immersed boundary method, and the predictions show good agreement with previous computational and experimental results. Finally, the flow induced by realistic human walking motion is simulated as an example of a problem involving multiple moving immersed objects.}, number={2}, journal={JOURNAL OF COMPUTATIONAL PHYSICS}, author={Choi, Jung-Il and Oberoi, Roshan C. and Edwards, Jack R. and Rosati, Jacky A.}, year={2007}, month={Jun}, pages={757–784} }
@article{xiao_hassan_edwards_gaffney_2007, title={Role of turbulent Prandtl numbers on heat flux at hypersonic Mach numbers}, volume={45}, DOI={10.2514/1.2144}, number={4}, journal={AIAA Journal}, author={Xiao, X. and Hassan, H. A. and Edwards, J. R. and Gaffney, R. L.}, year={2007}, pages={806–813} }
@article{neaves_edwards_2006, title={All-speed time-accurate underwater projectile calculations using a preconditioning algorithm}, volume={128}, ISSN={["1528-901X"]}, DOI={10.1115/1.2169816}, abstractNote={An algorithm based on the combination of time-derivative preconditioning strategies with low-diffusion upwinding methods is developed and applied to multiphase, compressible flows characteristic of underwater projectile motion. Multiphase compressible flows are assumed to be in kinematic and thermodynamic equilibrium and are modeled using a homogeneous mixture formulation. Compressibility effects in liquid-phase water are modeled using a temperature-adjusted Tait equation, and gaseous phases (water vapor and air) are treated as an ideal gas. The algorithm is applied to subsonic and supersonic projectiles in water, general multiphase shock tubes, and a high-speed water entry problem. Low-speed solutions are presented and compared to experimental results for validation. Solutions for high-subsonic and transonic projectile flows are compared to experimental imaging results and theoretical results. Results are also presented for several multiphase shock tube calculations. Finally, calculations are presented for a high-speed axisymmetric supercavitating projectile during the important water entry phase of flight.}, number={2}, journal={JOURNAL OF FLUIDS ENGINEERING-TRANSACTIONS OF THE ASME}, author={Neaves, MD and Edwards, JR}, year={2006}, month={Mar}, pages={284–296} }
@article{star_edwards_lin_cox-stouffer_jackson_2006, title={Numerical simulation of injection of supercritical ethylene into nitrogen}, volume={22}, ISSN={["1533-3876"]}, DOI={10.2514/1.16621}, abstractNote={A procedure for simulating the injection of supercritical ethylene into nitrogen is used to investigate aspects of the injection of supercritical fuels, considered to be an enabling technology in the design of hydrocarbons-fueled scramjet engines. The method solves the compressible Navier-Stokes equations for an ethylene/nitrogen mixture, with the thermodynamic behavior of ethylene described using the Peng-Robinson equation of state. Homogeneous equilibrium and finite-rate phase-transition models are used to describe the growth of a condensed ethylene phase in several axisymmetric and three-dimensional injector nozzles. Predictions are compared with shadowgraph and direct-lighting imaging data, mass flow rate measurements, mole-fraction and temperature measurements in the jet mixing zone, and wall pressure distributions. Qualitative trends relating to jet structure, the appearance of a condensed phase, and the effects of back pressure and injectant temperature are in good agreement with experimental results but indicate the need for improved characterization of the nozzle flow before injection and the inclusion of a better turbulence model for the jet mixing zone. For conditions where both are applicable, a nucleation/ growth phase transition model provides a similar bulk fluid response as a homogeneous equilibrium model but also yields predictions of number density and average droplet size.}, number={4}, journal={JOURNAL OF PROPULSION AND POWER}, author={Star, Ana M. and Edwards, Jack R. and Lin, Kuo-Cheng and Cox-Stouffer, Susan and Jackson, Thomas A.}, year={2006}, pages={809–819} }
@article{mao_edwards_harvey_2006, title={Prediction of foam growth and its nucleation in free and limited expansion}, volume={61}, ISSN={["1873-4405"]}, DOI={10.1016/j.ces.2005.07.026}, abstractNote={The influence volume approach (IVA) is often utilized for modeling the mass transfer process dictating bubble growth dynamics in physical foaming. However, the assumed concentration profile in the IVA method is only valid when the changes in dissolved gas concentration are small (less than 5%). In addition, the validity of the IVA method is difficult to justify in chemical foaming applications because of the difficulties involved in defining the dissolved gas concentration profile. In the present work, we define two distinct stages of bubble growth for physical foaming. These two stages are termed as free and limited expansion and are controlled by the bubble nucleation rate. Bubble nucleation is assumed to occur only in the free expansion stage. In this stage, the bubble pressure drops substantially from an initially high pressure in the supersaturated state while the dissolved gas concentration changes very little. The second stage of our two-stage mass transfer model is termed the limited expansion stage and accounts for bubble growth in the late stages of foam evolution, when the pressure changes become small. However, in the limited stage of bubble growth the dissolved gas concentration drops significantly, as the available dissolved gas is depleted. To summarize our two-stage mass transfer model of foam expansion, the pressure difference between the bubble phase and the liquid phase is the primary mechanism for driving mass transfer in the early (free) stages of foam growth and the concentration difference is the driver for bubble growth in the late (limited) stages of growth. The first stage can be regarded as the nucleation stage and it is relatively short; while the second stage can be regarded as the bubble growth stage and is much longer. Most of the bubble volume expansion takes place in the second stage. The concentration gradient at the bubble edge, which is often ignored in other models, is analyzed in detail in this paper. The details of our novel mass transfer model are also presented.}, number={6}, journal={CHEMICAL ENGINEERING SCIENCE}, author={Mao, DM and Edwards, JR and Harvey, A}, year={2006}, month={Mar}, pages={1836–1845} }
@article{xiao_edwards_hassan_cutler_2006, title={Variable turbulent Schmidt-number formulation for scramjet applications}, volume={44}, ISSN={["0001-1452"]}, DOI={10.2514/1.15450}, abstractNote={In high speed engines, thorough turbulent mixing of fuel and air is required to obtain high performance and high efficiency. Thus, the ability to predict turbulent mixing is crucial in obtaining accurate numerical simulation of an engine and its performance. Current state of the art in CFD simulation is to assume both turbulent Prandtl number and Schmidt numbers to be constants. However, since the mixing of fuel and air is inversely proportional to the Schmidt number, a value of 0.45 for the Schmidt number will produce twice as much diffusion as that with a value of 0.9. Because of this, current CFD tools and models have not been able to provide the needed guidance required for the efficient design of a scramjet engine. The goal of this investigation is to develop the framework needed to calculate turbulent Prandtl and Schmidt numbers as part of the solution. This requires four additional equations: two for the temperature variance and its dissipation rate and two for the concentration variance and its dissipation rate. In the current investigation emphasis will be placed on studying mixing without reactions. For such flows, variable Prandtl number does not play a major role in determining the flow. This, however, will have to be addressed when combustion is present. The approach to be used is similar to that used to develop the k-zeta model. In this approach, relevant equations are derived from the exact Navier-Stokes equations and each individual correlation is modeled. This ensures that relevant physics is incorporated into the model equations. This task has been accomplished. The final set of equations have no wall or damping functions. Moreover, they are tensorially consistent and Galilean invariant. The derivation of the model equations is rather lengthy and thus will not be incorporated into this abstract, but will be included in the final paper. As a preliminary to formulating the proposed model, the original k-zeta model with constant turbulent Prandtl and Schmidt numbers is used to model the supersonic coaxial jet mixing experiments involving He, O2 and air.}, number={3}, journal={AIAA JOURNAL}, author={Xiao, X and Edwards, JR and Hassan, HA and Cutler, AD}, year={2006}, month={Mar}, pages={593–599} }
@article{xiao_edwards_hassan_2004, title={Blending functions in hybrid large-eddy/Reynolds-averaged Navier-Stokes simulations}, volume={42}, ISSN={["0001-1452"]}, DOI={10.2514/1.2094}, abstractNote={Several blending functions for use in hybrid large-eddy simulation (LES)/Reynolds-averaged Navier-Stokes (RANS) simulations of shock-separated flows are tested. The blending functions shift the turbulence closure from a k-ζ turbulence model near solid surfaces to a k − ∆ subgrid closure away from the wall. Three distinct forms for the blending function are developed: one that depends on the ratio of the von Karman length scale and the Taylor microscale, another that depends on the ratio of the RANS eddy viscosity to the subgrid eddy viscosity, and a third which replaces the von Karman length scale in the first form with the distance to the nearest wall. Comparisons are made for two cases: Mach 2.79 flow over a 20-deg compression corner and Mach 2.88 flow over a 25-deg compression/expansion corner. boundary conditions for all calculations employ the rescaling/reintroducing procedure developed by Xiao et al. (Xiao, X., Edwards, J. R., Hassan, H. A., and Baurle, R. A., Inflow Boundary Conditions for Hybrid Large Eddy/Reynolds Averaged Navier-Stokes Simulations, AIAA Journal ,V ol. 41, No. 8, 2003, pp. 1481-1489) for hybrid LES/RANS simulations of wall-bounded flows. In general, the blending function based on the von Karman length scale gives the best results when compared with measured data. The skin friction predictions show the highest sensitivity to the various blending functions.}, number={12}, journal={AIAA JOURNAL}, author={Xiao, X and Edwards, JR and Hassan, HA}, year={2004}, month={Dec}, pages={2508–2515} }
@article{bond_edwards_2004, title={Computational analysis of an independent ramjet stream in a combined cycle engine}, volume={42}, ISSN={["1533-385X"]}, DOI={10.2514/1.4465}, abstractNote={A new concept for the low-speed propulsion mode in rocket-based combined cycle engines has been developed as part of the NASA GTX program. This concept, called the independent ramjet stream (IRS) cycle, is a variation of the traditional ejector ramjet (ER) design and involves the injection of hydrogen fuel directly into the airstream, where it is ignited by the rocket plume. The advantage of the IRS design is that it allows for a single large rocket instead of several smaller rockets, and its required combustor length is smaller than that of a traditional ER design. Both of these features make the IRS design lighter. Experiments and computational fluid dynamics are currently being used to evaluate the feasibility of the new design. In this work, a Navier‐Stokes code valid for general reactive flows is applied to the model engine under cold-flow, ER, and IRS cycle operation. Pressure distributions corresponding to cold-flow and ER operation are compared with experimental data. The engine response under IRS cycle operation is examined for different reaction models and grid sizes. The solutions exhibit a high sensitivity to both grid resolution and reaction mechanism but do indicate that thermal throat ramjet operation is possible through the injection and burning of additional fuel into the airstream.}, number={11}, journal={AIAA JOURNAL}, author={Bond, RB and Edwards, JR}, year={2004}, month={Nov}, pages={2276–2283} }
@article{fan_xiao_edwards_hassan_2004, title={Hybrid large-eddy/Reynolds-averaged Navier-Stokes simulations of shock-separated flows}, volume={41}, ISSN={["1533-6794"]}, DOI={10.2514/1.3735}, abstractNote={Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.}, number={6}, journal={JOURNAL OF SPACECRAFT AND ROCKETS}, author={Fan, CC and Xiao, XD and Edwards, JR and Hassan, HA}, year={2004}, pages={897–906} }
@article{mao_edwards_kuznetsov_srivastava_2004, title={Three-dimensional numerical simulation of a circulating fluidized bed reactor for multi-pollutant control}, volume={59}, ISSN={["0009-2509"]}, DOI={10.1016/j.ces.2004.06.004}, abstractNote={Circulating fluidized bed adsorber (CFBA) technology is regarded as a potentially effective method for simultaneously controlling emissions of sulfur dioxide, fine particulate matter, and trace heavy metals, such as mercury vapor. In order to analyze CFBA systems in detail, a gas mixture/solids mixture model based on the three-dimensional Navier–Stokes equations is developed for particle flow, agglomeration, physical and chemical adsorption in a circulating fluidized bed. The solids mixture consists of two solids, one with components of CaO and CaSO4, and the other being an activated carbon. The gas mixture is composed of fine particulate matter (PM), sulfur dioxide, mercury vapor, oxygen and inert gas. Source terms representing fine particulate matter agglomeration onto sorbent particles, sulfur dioxide removal through chemical adsorption onto calcined lime, and mercury vapor removal through physical adsorption onto activated carbon are formulated and included into the model. The governing equations are solved using high-resolution upwind-differencing methods, combined with a time-derivative preconditioning method for efficient time-integration. Numerical simulations of bench-scale operation of a prototype CFBA reactor for multi-pollutant control are described.}, number={20}, journal={CHEMICAL ENGINEERING SCIENCE}, author={Mao, DM and Edwards, JR and Kuznetsov, AV and Srivastava, RK}, year={2004}, month={Oct}, pages={4279–4289} }
@article{mao_edwards_kuznetsov_srivastava_2003, title={Development of low-diffusion flux-splitting methods for dense gas-solid flows}, volume={185}, ISSN={["1090-2716"]}, DOI={10.1016/S0021-9991(02)00049-9}, abstractNote={The development of a class of low-diffusion upwinding methods for computing dense gas-solid flows is presented in this work. An artificial compressibility/low-Mach preconditioning strategy is developed for a hyperbolic two-phase flow equation system consisting of separate solids and gas momentum and continuity equations. The eigenvalues of this system are used to devise extensions of the AUSM+ [1] and LDFSS [2] flux-splitting methods that provide high resolution capturing of bubble growth and collapse in gas-solid fluidized beds. Applications to several problems in fluidization are presented.}, number={1}, journal={JOURNAL OF COMPUTATIONAL PHYSICS}, author={Mao, DM and Edwards, JR and Kuznetsov, AV and Srivastava, RK}, year={2003}, month={Feb}, pages={100–119} }
@article{baurle_tam_edwards_hassan_2003, title={Hybrid simulation approach for cavity flows: Blending, algorithm, and boundary treatment issues}, volume={41}, ISSN={["0001-1452"]}, DOI={10.2514/2.2129}, abstractNote={The maturation of high-performance computer architectures and computational algorithms has prompted the development of a new generation of models that attempt to combine the robustness and efficiency offered by the Reynolds averaged Navier-Stokes equations with the higher level of modeling offered by the equations developed for large eddy simulation. The application of a new hybrid approach is discussed, where the transition between these equation sets is controlled by a blending function that depends on local turbulent flow properties, as well as the local mesh spacing. The utilization of local turbulence properties provides added control in specifying the regions of the flow intended for each equation set, removing much of the burden from the grid-generation process. Moreover, the model framework allows for the combination of existing closure model equations, avoiding the difficulty of formulating a single set of closure coefficients that perform well in both Reynolds averaged and large eddy simulation modes. Simple modifications to common second-order accurate Reynolds averaged Navier-Stokes algorithms are proposed to enhance the capturing of large eddy motions}, number={8}, journal={AIAA JOURNAL}, author={Baurle, RA and Tam, CJ and Edwards, JR and Hassan, HA}, year={2003}, month={Aug}, pages={1463–1480} }
@article{xiao_edwards_hassan_baurle_2003, title={Inflow boundary conditions for hybrid large eddy/Reynolds averaged Navier-Stokes simulations}, volume={41}, ISSN={["0001-1452"]}, DOI={10.2514/2.2130}, abstractNote={Inflow boundary conditions are developed for hybrid large-eddy simulation (LES)/Reynolds-averaged Navier-Stokes approaches. They are based on an extension of the rescaling-reintroducing method developed for LES to a hybrid scheme. A blending function is used to shift the turbulence closure from a κ-ζ model near the wall to a κ-Δ subgrid-scale model away from the wall. The approach was tested for a flat plate and then applied to the study of a 25-deg compression-expansion ramp for a Mach number of 2.88 and a Reynolds number of 3.24 × 10 7 /m. In general, improvements over the κ-ζ model were noted in the recovery region. The significance of this work is that it provides a way for LES methods to address flows at a high Reynolds number}, number={8}, journal={AIAA JOURNAL}, author={Xiao, XD and Edwards, JR and Hassan, HA and Baurle, RA}, year={2003}, month={Aug}, pages={1481–1489} }
@article{mao_edwards_kuznetsov_srivastava_2002, title={A model for fine particle agglomeration in circulating fluidized bed absorbers}, volume={38}, ISSN={["0947-7411"]}, DOI={10.1007/S002310100260}, number={4-5}, journal={HEAT AND MASS TRANSFER}, author={Mao, D and Edwards, JR and Kuznetsov, AV and Srivastava, R}, year={2002}, month={Apr}, pages={379–388} }
@article{mao_edwards_kuznetsov_srivastava_2002, title={Particle flow, mixing, and chemical reaction in circulating fluidized bed absorbers}, volume={57}, ISSN={["0009-2509"]}, DOI={10.1016/S0009-2509(02)00168-9}, abstractNote={Abstract A mixing model has been developed to simulate the particle residence time distribution (RTD) in a circulating fluidized bed absorber (CFBA). Also, a gas/solid reaction model for sulfur dioxide (SO 2 ) removal by lime has been developed. For the reaction model that considers RTD distribution inside the core and annulus regions of a CFBA, a macrochemical reaction can be simulated based on microchemical reaction dynamics. The presented model can predict SO 2 and lime concentration distributions inside the CFBA, and give the amount of lime needed to remove a given percentage of SO 2 . It is found that SO 2 concentration decreases with the increase of CFBA distance from the bottom in the core region. However, lime concentration exhibits a very slight variation in the core region. This means that lime is efficiently utilized to remove SO 2 . The model also predicts that SO 2 partial pressure at the exit of the CFBA decreases with the increase in the percentage of fresh lime injected in the CFBA.}, number={15}, journal={CHEMICAL ENGINEERING SCIENCE}, author={Mao, D and Edwards, JR and Kuznetsov, AV and Srivastava, R}, year={2002}, month={Aug}, pages={3107–3117} }
@article{edwards_srivastava_kilgroe_2001, title={A study of gas-phase mercury speciation using detailed chemical kinetics}, volume={51}, ISSN={["1047-3289"]}, DOI={10.1080/10473289.2001.10464316}, abstractNote={Mercury speciation in combustion-generated flue gas was modeled using a detailed chemical mechanism consisting of 60 reactions and 21 species. This speciation model accounts for the chlorination and oxidation of key flue-gas components, including elemental mercury (Hg0). Results indicated that the performance of the model is very sensitive to temperature. Starting with pure HCl, for lower reactor temperatures (less than approximately 630 degrees C), the model produced only trace amounts of atomic and molecular chlorine (Cl and Cl2), leading to a drastic underprediction of Hg chlorination compared with experimental data. For higher reactor temperatures, model predictions were in good accord with experimental data. For conditions that produce an excess of Cl and Cl2 relative to Hg, chlorination of Hg is determined by the competing influences of the initiation step, Hg + Cl = HgCl, and the Cl recombination reaction, 2Cl = Cl2. If the Cl recombination reaction is faster, Hg chlorination will eventually be dictated by the slower pathway Hg + Cl2 = HgCl2.}, number={6}, journal={JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION}, author={Edwards, JR and Srivastava, RK and Kilgroe, JD}, year={2001}, month={Jun}, pages={869–877} }
@article{edwards_roy_blottner_hassan_2001, title={Development of a one-equation Transition/Turbulence model}, volume={39}, ISSN={["1533-385X"]}, DOI={10.2514/2.1526}, abstractNote={This paper reports on the development of a unified one-equation model for the prediction of transitional and turbulent flows. An eddy viscosity - transport equation for non-turbulent fluctuation growth based on that proposed by Warren and Hassan (Journal of Aircraft, Vol. 35, No. 5) is combined with the Spalart-Allmaras one-equation model for turbulent fluctuation growth. Blending of the two equations is accomplished through a multidimensional intermittence function based on the work of Dhawan and Narasimha (Journal of Fluid Mechanics, Vol. 3, No. 4). The model predicts both the onset and extent of transition. Low-speed test cases include transitional flow over a flat plate, a single element airfoil, and a multi-element airfoil in landing configuration. High-speed test cases include transitional Mach 3.5 flow over a 5{degree} cone and Mach 6 flow over a flared-cone configuration. Results are compared with experimental data, and the spatial accuracy of selected predictions is analyzed.}, number={9}, journal={AIAA JOURNAL}, author={Edwards, JR and Roy, CJ and Blottner, FG and Hassan, HA}, year={2001}, month={Sep}, pages={1691–1698} }
@article{chernyak_henon_harris_gould_franklin_edwards_desimone_carbonell_2001, title={Formation of perfluoropolyether coatings by the rapid expansion of supercritical solutions (RESS) process. Part 1: Experimental results}, volume={40}, ISSN={["0888-5885"]}, DOI={10.1021/ie010267m}, abstractNote={The rapid expansion of supercritical solutions (RESS) process is a promising environmentally benign technology for fine droplet or particle formation. The absence of organic solvents and narrow size distribution of RESS precipitates make this process attractive for polymer coating applications. In our work, this technique has been used to produce droplets of perfluoropolyethers from CO2 solutions without the aid of cosolvents for the coating of porous materials applied in monumental and civil infrastructures. The present work is aimed at gaining an understanding of the relationship between droplet and spray characteristics and RESS process conditions. As such, a combined experimental/computational approach is applied to a representative binary system consisting of a low-molecular-weight perfluoropolyether diamide (PFD) dissolved in supercritical CO2. Part 1 of this work presents phase equilibria measurements and polymer droplet size characterizations under different operating conditions. The effects of temperature, solute concentration, and nozzle configuration on droplet and spray characterization and transfer efficiency are discussed. Part 2 of this work presents a multidimensional computational fluid dynamics model of the RESS expansion process and describes the use of the model in further analyzing and interpreting experimental data.}, number={26}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Chernyak, Y and Henon, F and Harris, RB and Gould, RD and Franklin, RK and Edwards, JR and DeSimone, JM and Carbonell, RG}, year={2001}, month={Dec}, pages={6118–6126} }
@article{franklin_edwards_chernyak_gould_henon_carbonell_2001, title={Formation of perfluoropolyether coatings by the rapid expansion of supercritical solutions (RESS) process. Part 2: Numerical modeling}, volume={40}, ISSN={["0888-5885"]}, DOI={10.1021/ie010268e}, abstractNote={The rapid expansion of supercritical solutions (RESS) process is a promising method for the production of ultrafine powders and aerosols of narrow size distribution for coatings and other applications. In this article, part 2 of a two-part study, the nucleation and subsequent growth of 2500 Mw perfluoropolyether diamide (PFD) from supercritical carbon dioxide (CO2) by expansion through a small-diameter nozzle is modeled in a three-stage, multidimensional fashion. The stages include a hydrodynamic solution, solvent−solute phase equilibria analyses, and an aerosol transport model. The hydrodynamics model successfully captures the vapor−liquid transition that occurs as carbon dioxide is expanded to ambient conditions. Cloud-point pressures and equilibrium compositions of the separated solvent−solute system are determined and are used in a multidimensional aerosol transport model. This model incorporates various mechanisms influencing droplet growth. Parametric studies are conducted to investigate the influences of the interfacial tension, the equilibrium addition of carbon dioxide, and the diffusion coefficient on the predicted droplet diameter. Turbulent coagulation in the ambient region downstream of the expansion nozzle is found to be the dominant mechanism responsible for the production of micron-sized droplets observed in companion experiments.}, number={26}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Franklin, RK and Edwards, JR and Chernyak, Y and Gould, RD and Henon, F and Carbonell, RG}, year={2001}, month={Dec}, pages={6127–6139} }
@article{xiao_edwards_hassan_2001, title={Transitional flow over an elliptic cone at Mach 8}, volume={38}, ISSN={["0022-4650"]}, DOI={10.2514/2.3767}, abstractNote={Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.}, number={6}, journal={JOURNAL OF SPACECRAFT AND ROCKETS}, author={Xiao, XD and Edwards, JR and Hassan, HA}, year={2001}, pages={941–945} }
@article{edwards_thomas_2000, title={Development of O(Nm(2)) preconditioned multigrid solvers for Euler and Navier-Stokes equations}, volume={38}, ISSN={["0001-1452"]}, DOI={10.2514/2.1018}, number={4}, journal={AIAA JOURNAL}, author={Edwards, JR and Thomas, JL}, year={2000}, month={Apr}, pages={717–720} }
@article{edwards_franklin_liou_2000, title={Low-diffusion flux-splitting methods for real fluid flows with phase transitions}, volume={38}, DOI={10.2514/2.1145}, abstractNote={Methods for extending the AUSM+ low-diffusion flux-splitting scheme toward the calculation of real fluid flows at all speeds are presented. The single-phase behavior of the fluid is defined by the Sanchez-Lacombe equation of state, a lattice-fluid description. Liquid-vapor phase transitions are modeled through a homogeneous equilibrium approach. Time-derivative preconditioning is utilized to allow effective integration of the equation system at all flow speeds and all states of compressibility. Modifications to the preconditioned variant of AUSM+ necessary to preserve solution accuracy under such conditions are presented in detail. One-dimensional results are presented for the faucet problem, a classic test case for multifluid algorithms, as well as for liquid octane flow through a converging-diverging nozzle. Two-dimensional calculations are presented for water flow over a hemisphere/cylinder geometry and liquid carbon dioxide flow through a capillary nozzle}, number={9}, journal={AIAA Journal}, author={Edwards, J. R. and Franklin, R. K. and Liou, M. S.}, year={2000}, pages={1624–1633} }
@article{roy_edwards_2000, title={Numerical simulation of a three-dimensional flame/shock wave interaction}, volume={38}, ISSN={["0001-1452"]}, DOI={10.2514/2.1035}, abstractNote={A three-dimensional Navier-Stokes solver for chemically reacting flows is used to study the structure of a supersonic hydrogen-air flame stabilized in a Mach 2.4 rectangular cross-section wind tunnel. The numerical model uses a 9-species, 21-reaction hydrogen oxidation mechanism and employs Menter's hybrid κ-ω/κ-e turbulence model. An assumed probability density function is used to account for the effects of turbulent temperature fluctuations on the ensemble-averaged chemical reaction rates. Results are presented for a configuration studied at the University of Michigan in which the effects of wedge-generated shock waves on flame stability were determined. Computed pitot and static pressure profiles are compared with experimental measurements, and axial density gradient contour plots are compared with experimental schlieren photographs. The highly three-dimensional structure of the flame is described in detail, and stabilization mechanisms are discussed}, number={5}, journal={AIAA JOURNAL}, author={Roy, CJ and Edwards, JR}, year={2000}, month={May}, pages={745–754} }
@article{czerwiec_edwards_rumsey_bertelrud_hassan_2000, title={Study of high-lift configurations using k-zeta transition/turbulence model}, volume={37}, ISSN={["0021-8669"]}, DOI={10.2514/2.2728}, abstractNote={The flow over the multi-element McDonnell Douglas configuration is computed using the κ-ζ transition/turbulence model. The model is capable of calculating transition onset as part of the solution at a cost comparable to Navier-Stokes solvers that employ two-equation models. The model is first incorporated into CFL3D and then used to calculate flows for two angles of attack, 8 and 19 deg, at a freestream Mach number of 0.2 and a Reynolds number of 9 x 10 6 . In general, good agreement is indicated for predicting transition onset and velocity profiles over sections of the main airfoil and flap. Most of the differences between computation and experiment are in the prediction of the extent and penetration of the slat wake at the 19-deg angle-of-attack case. Even for this case relative differences were less than 5%}, number={6}, journal={JOURNAL OF AIRCRAFT}, author={Czerwiec, R and Edwards, JR and Rumsey, CL and Bertelrud, A and Hassan, HA}, year={2000}, pages={1008–1016} }
@article{edwards_liou_1998, title={Low-diffusion flux-splitting methods for flows at all speeds}, volume={36}, ISSN={["0001-1452"]}, DOI={10.2514/2.587}, abstractNote={Methods for extending the advective upwind splitting method (AUSM) family of low-diffusion flux-splitting schemes to operate effectively at all flow speeds are developed. The extensions developed are designed for use with time-derivative preconditioning and are based on the idea that the speed of sound should cease to be an important scaling parameter for the diffusive contributions to the interface flux as the Mach number becomes small. Using this criterion, alternative definitions for the interface Mach numbers are developed, and methods for ensuring pressure-velocity coupling at low speeds are formulated. Results are presented for inviscid flows through a channel at various Mach numbers, developing viscous flow in a two-dimensional duct, driven-cavity flows at various Mach and Reynolds numbers, flow over a backward-facing step, and hydrogen-nitrogen mixing layers}, number={9}, journal={AIAA JOURNAL}, author={Edwards, JR and Liou, MS}, year={1998}, month={Sep}, pages={1610–1617} }
@article{edwards_roy_1998, title={Preconditioned multigrid methods for two-dimensional combustion calculations at all speeds}, volume={36}, ISSN={["0001-1452"]}, DOI={10.2514/2.7500}, abstractNote={The development of an effective implicit integration strategy for two-dimensional (axisymmetric) combustion calculations at all speeds is presented. A time-derivative preconditioning technique is first combined with an implicit line relaxation algorithm to yield an approach capable of removing the acoustic time step restriction at low flow speeds while handling stiff chemical kinetics in a fully implicit fashion. Numerical performance is further improved through the addition of a full multigrid/full approximation storage (FMG-FAS) convergence acceleration strategy. Numerical simulations of a subsonic reacting shear layer (finite rate hydrogen-air chemistry), a subsonic bluff-body stabilized flame (mixing-limited methane-air chemistry), and a supersonic jet diffusion flame (finite rate hydrogen-air chemistry) are presented to test the basic attributes of the algorithm. Comparisons with experimental data are presented for all cases, and a detailed examination of the computational efficiency of the new procedure is conducted. The strengths and weaknesses of multigrid ideas for fully coupled combustion calculations are particularly highlighted.}, number={2}, journal={AIAA JOURNAL}, author={Edwards, JR and Roy, CJ}, year={1998}, month={Feb}, pages={185–192} }
@article{edwards_1997, title={A low-diffusion flux-splitting scheme for Navier-Stokes calculations}, volume={26}, ISSN={["0045-7930"]}, DOI={10.1016/S0045-7930(97)00014-5}, number={6}, journal={COMPUTERS & FLUIDS}, author={Edwards, JR}, year={1997}, month={Jul}, pages={635–659} }
@article{nyahoro_johnson_edwards_1997, title={Simulated performance of thermal storage in a solar cooker}, volume={59}, ISSN={["0038-092X"]}, DOI={10.1016/S0038-092X(96)00133-8}, abstractNote={An explicit finite-difference method is used to simulate the thermal performance of short-term thermal storage for a focusing, indoor, institutional, solar cooker. The cooker storage unit consists of a cylindrical solid block. The block is enclosed in a uniform layer of insulation except where there are cavities on the top and bottom surfaces to alllow heating of a pot from storage and heating of the storage by solar radiation. A paraboloidal concentrator focuses solar radiation through a secondary reflector onto a central circular zone of the storage block through the cavity in the insulation. The storage is charged for a set period of time and heat is subsequently discharged to a pot of water. In these simulations a pot of cold water is placed on the hot storage block and the time then estimated until the water either boils or the temprature of the water reaches a maximum value. Simulations are made for a given pot capacity with the storage block made from either cast iron or granite (rock). The effects on cooker performance are compared for a variety of height to diameter ratios of the storage block and size of the area of solar input zone.}, number={1-3}, journal={SOLAR ENERGY}, author={Nyahoro, PK and Johnson, RR and Edwards, J}, year={1997}, pages={11–17} }
@article{gaitonde_shang_edwards_1997, title={Structure of a supersonic three-dimensional cylinder/offset-flare turbulent interaction}, volume={34}, ISSN={["0022-4650"]}, DOI={10.2514/2.3232}, abstractNote={Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.}, number={3}, journal={JOURNAL OF SPACECRAFT AND ROCKETS}, author={Gaitonde, D and Shang, JS and Edwards, JR}, year={1997}, pages={294–302} }