Reynolds-averaged Navier-Stokes/large-eddy simulations of supersonic base flow

Several zonal and nonzonal hybrid Reynolds-averaged Navier-Stokes/large-eddy simulation approaches have been assessed to handle a high Reynolds number supersonic base flow. The results obtained on 5 and 13.5 x 10(6) points grids are compared to the available experimental data (Herrin, J. L., and Dutton, J. C., Supersonic Base Flow Experiments in the Near Wake of a Cylindrical Afterbody,AIAA Journal, Vol. 32, No. 77,1994), and the capabilities of these different methodologies to predict supersonic flows are discussed. The highly compressible separated shear layer proved to be a challenging issue for hybrid methods due to an alteration in the instability process (as compared to the incompressible case), leading to three-dimensional coherent structures. Numerous numerical parameters relevant to hybrid methods have been assessed. The incoming boundary layer thickness needs to be properly set, while a weak influence of the subgrid scale model is observed when small-scale structures in the separating mixing layer are resolved. Another finding of the present study is the dramatic influence displayed by the numerical dissipation on the flowfield. Sensitivity to the CDFS model constant is observed even with the finest grid, leading to a delay in the generation of instabilities in the shear layer.