@article{mettu_subbareddy_2022, title={Wall-Modeled Large Eddy Simulation of High Speed Flows}, ISSN={["1533-385X"]}, DOI={10.2514/1.J061501}, abstractNote={The use of wall-modeled large-eddy simulation (WMLES) is explored in the context of compressible flows with a focus on cold-wall boundary layers and flows with shock-induced separation. It is observed that for cold-wall flows, a “mixed” scaling for the length scale appearing in the eddy viscosity formulation outperforms the classical semilocal scaling for obtaining predictions of heat flux and skin friction. A few shock/boundary-layer interaction (SBLI) cases are examined in some detail, and model modifications are proposed to overcome identified deficiencies. It is shown that using WMLES the low-frequency characteristics of SBLI at high Reynolds number can be quantitatively captured. A dynamically switched version of the equilibrium model is proposed; this shows promise for relatively inexpensive simulations at these conditions.}, journal={AIAA JOURNAL}, author={Mettu, Balachandra R. and Subbareddy, Pramod K.}, year={2022}, month={Mar} }
@article{kartha_subbareddy_candler_2019, title={LES of Subsonic Reacting Mixing Layers}, ISBN={1573-1987}, DOI={10.1007/s10494-019-00066-4}, journal={FLOW TURBULENCE AND COMBUSTION}, author={Kartha, Anand and Subbareddy, Pramod K. and Candler, Graham V}, year={2019} }
@article{pickles_mettu_subbareddy_narayanaswamy_2019, title={On the mean structure of sharp-fin-induced shock wave/turbulent boundary layer interactions over a cylindrical surface}, volume={865}, ISSN={["1469-7645"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85061720934&partnerID=MN8TOARS}, DOI={10.1017/jfm.2019.53}, abstractNote={Interactions between an oblique shock wave generated by a sharp fin placed on a cylindrical surface and the incoming boundary layer are investigated to unravel the mean features of the resulting shock/boundary layer interaction (SBLI) unit. This fin-on-cylinder SBLI unit has several unique features caused by the three-dimensional (3-D) relief offered by the cylindrical surface that noticeably alter the shock structure. Complementary experimental and computational studies are made to delineate both the surface and off-body flow features of the fin-on-cylinder SBLI unit and to obtain a detailed understanding of the mechanisms that dictate the mean flow and wall pressure features of the SBLI unit. Results show that the fin-on-cylinder SBLI exhibits substantial deviation from quasi-conical symmetry that is observed in planar fin SBLI. Furthermore, the separated flow growth rate appears to decrease with downstream distance and the separation size is consistently smaller than the planar fin SBLI with the same inflow and fin configurations. The causes for the observed diminution of the separated flow and its downstream growth rate were investigated in the light of changes caused by the cylinder curvature on the inviscid as well as separation shock. It was found that the inviscid shock gets progressively weakened in the region close to the triple point with downstream distance due to the 3-D relief effect from cylinder curvature. This weakening of the inviscid shock feeds into the separation shock, which is also independently impacted by the 3-D relief, to result in the observed modifications in the fin-on-cylinder SBLI unit.}, journal={JOURNAL OF FLUID MECHANICS}, author={Pickles, J. D. and Mettu, B. R. and Subbareddy, P. K. and Narayanaswamy, V.}, year={2019}, month={Apr}, pages={212–246} }
@article{pickles_mettu_subbareddy_narayanaswamy_2018, title={Gas density field imaging in shock dominated flows using planar laser scattering}, volume={59}, ISSN={["1432-1114"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85048239189&partnerID=MN8TOARS}, DOI={10.1007/s00348-018-2562-8}, number={7}, journal={EXPERIMENTS IN FLUIDS}, author={Pickles, Joshua D. and Mettu, Balachandra R. and Subbareddy, Pramod K. and Narayanaswamy, Venkateswaran}, year={2018}, month={Jul} }
@article{subbareddy_kartha_candler_2017, title={Scalar conservation and boundedness in simulations of compressible flow}, volume={348}, ISSN={["1090-2716"]}, DOI={10.1016/j.jcp.2017.08.001}, abstractNote={With the proper combination of high-order, low-dissipation numerical methods, physics-based subgrid-scale models, and boundary conditions it is becoming possible to simulate many combustion flows at relevant conditions. However, non-premixed flows are a particular challenge because the thickness of the fuel/oxidizer interface scales inversely with Reynolds number. Sharp interfaces can also be present in the initial or boundary conditions. When higher-order numerical methods are used, there are often aphysical undershoots and overshoots in the scalar variables (e.g. passive scalars, species mass fractions or progress variable). These numerical issues are especially prominent when low-dissipation methods are used, since sharp jumps in flow variables are not always coincident with regions of strong variation in the scalar fields: consequently, special detection mechanisms and dissipative fluxes are needed. Most numerical methods diffuse the interface, resulting in artificial mixing and spurious reactions. In this paper, we propose a numerical method that mitigates this issue. We present methods for passive and active scalars, and demonstrate their effectiveness with several examples.}, journal={JOURNAL OF COMPUTATIONAL PHYSICS}, author={Subbareddy, Pramod K. and Kartha, Anand and Candler, Graham V.}, year={2017}, month={Nov}, pages={827–846} }
@article{brock_subbareddy_candler_2015, title={Detached-Eddy Simulations of Hypersonic Capsule Wake Flow}, volume={53}, ISSN={["1533-385X"]}, DOI={10.2514/1.j052771}, abstractNote={Numerical simulations are performed on a spherical capsule model based on the Orion Crew Exploration Vehicle and compared to experimental data obtained at the Calspan University of Buffalo Research Center. The flow is at Mach 6.4, and a case with an angle of attack of 28 deg is considered. The interest is in predictions of afterbody heating in the presence of massive separation and the resultant highly unsteady wake flow. Detached-eddy simulations of this flowfield are done using several flux schemes, and the effect of mesh refinement is considered. The results are compared to experimental data for mean and fluctuating heat transfer in the separated portion of the afterbody. Comparisons of instantaneous flow features are presented to illustrate varying levels of resolved scales.}, number={1}, journal={AIAA JOURNAL}, author={Brock, Joseph M. and Subbareddy, Pramod K. and Candler, Graham V.}, year={2015}, month={Jan}, pages={70–80} }
@article{subbareddy_bartkowicz_candler_2014, title={Direct numerical simulation of high-speed transition due to an isolated roughness element}, volume={748}, ISSN={0022-1120 1469-7645}, url={http://dx.doi.org/10.1017/JFM.2014.204}, DOI={10.1017/JFM.2014.204}, abstractNote={Abstract We study the transition of a Mach 6 laminar boundary layer due to an isolated cylindrical roughness element using large-scale direct numerical simulations (DNS). Three flow conditions, corresponding to experiments conducted at the Purdue Mach 6 quiet wind tunnel are simulated. Solutions are obtained using a high-order, low-dissipation scheme for the convection terms in the Navier–Stokes equations. The lowest Reynolds number ( $Re$ ) case is steady, whereas the two higher $Re$ cases break down to a quasi-turbulent state. Statistics from the highest $Re$ case show the presence of a wedge of fully developed turbulent flow towards the end of the domain. The simulations do not employ forcing of any kind, apart from the roughness element itself, and the results suggest a self-sustaining mechanism that causes the flow to transition at a sufficiently large Reynolds number. Statistics, including spectra, are compared with available experimental data. Visualizations of the flow explore the dominant and dynamically significant flow structures: the upstream shock system, the horseshoe vortices formed in the upstream separated boundary layer and the shear layer that separates from the top and sides of the cylindrical roughness element. Streamwise and spanwise planes of data were used to perform a dynamic mode decomposition (DMD) (Rowley et al. , J. Fluid Mech. , vol. 641, 2009, pp. 115–127; Schmid, J. Fluid Mech. , vol. 656, 2010, pp. 5–28).}, journal={Journal of Fluid Mechanics}, publisher={Cambridge University Press (CUP)}, author={Subbareddy, Pramod K. and Bartkowicz, Matthew D. and Candler, Graham V.}, year={2014}, month={May}, pages={848–878} }
@article{candler_subbareddy_nompelis_2013, title={Decoupled Implicit Method for Aerothermodynamics and Reacting Flows}, volume={51}, ISSN={["0001-1452"]}, DOI={10.2514/1.j052070}, abstractNote={We propose a new implicit computational fluid dynamics method for steady-state compressible reacting flows. The concept is to decouple the total mass, momentum, and energy conservation equations from the species mass and internal energy equations and to solve the two equation sets sequentially. With certain approximations to the implicit system, it is possible to dramatically reduce the cost of the solution with little to no penalty on the convergence properties. Importantly, the cost of the decoupled implicit problem scales linearly with the number of species, as opposed to the quadratic scaling for the conventional fully coupled method. Furthermore, the new approach reduces the memory requirements by a significant factor. The decoupled implicit method shows promise for the application to aerothermodynamics problems and reacting flows.}, number={5}, journal={AIAA JOURNAL}, author={Candler, Graham V. and Subbareddy, Pramod K. and Nompelis, Ioannis}, year={2013}, month={May}, pages={1245–1254} }
@article{subbareddy_candler_2009, title={A fully discrete, kinetic energy consistent finite-volume scheme for compressible flows}, volume={228}, ISSN={["0021-9991"]}, DOI={10.1016/j.jcp.2008.10.026}, abstractNote={A robust, implicit, low-dissipation method suitable for LES/DNS of compressible turbulent flows is discussed. The scheme is designed such that the discrete flux of kinetic energy and its rate of change are consistent with those predicted by the momentum and continuity equations. The resulting spatial fluxes are similar to those derived using the so-called skew-symmetric formulation of the convective terms. Enforcing consistency for the time derivative results in a novel density weighted Crank–Nicolson type scheme. The method is stable without the addition of any explicit dissipation terms at very high Reynolds numbers for flows without shocks. Shock capturing is achieved by switching on a dissipative flux term which tends to zero in smooth regions of the flow. Numerical examples include a one-dimensional shock tube problem, the Taylor–Green problem, simulations of isotropic turbulence, hypersonic flow over a double-cone geometry, and compressible turbulent channel flow.}, number={5}, journal={JOURNAL OF COMPUTATIONAL PHYSICS}, author={Subbareddy, Pramod K. and Candler, Graham V.}, year={2009}, month={Mar}, pages={1347–1364} }