@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{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{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{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{joung_choi_choi_2007, title={Direct numerical simulation of turbulent flow in a square duct: Analysis of secondary flows}, volume={133}, DOI={10.1061/(ASCE)0733-9399(2007)133:(213)}, number={2}, journal={Journal of Engineering Mechanics}, author={Joung, Y. and Choi, S. U. and Choi, J. I.}, year={2007}, pages={213–221} }