Computational study of supersonic base flow using hybrid turbulence methodology

Large-eddy simulation/Reynolds-averaged Navier--Stokes (LES/RANS) hybrid methodology is applied to a high-Reynolds-number supersonic axisymmetric base flow. Accurate predictions of the base flowfield and base pressure are successfully achieved by using the LES/RANS hybrid methodology with less computational cost than that of pure LES and monotone integrated large-eddy simulation (MILES) approaches. Both the efficiency and reliability of the present LES/RANS hybrid methodology for the prediction of massively separated high-Reynolds-number flows are identified by comparison with the results obtained by LES, MILES, RANS, and the experiments in detail. The LES/RANS hybrid simulation accurately resolves the physics of unsteady turbulent motions, such as shear-layer rollup, large-eddy motions in the downstream region, small-eddy motions inside the recirculating region, and formation of large mushroom-shaped patterns in the end view. Comparison of the results shows that it is necessary to resolve approaching boundary layers and free shear-layer velocity profiles from the base edge correctly for the accurate prediction of base flows. Given the required mesh resolution near solid surfaces for pure LES and MILES at high-Reynolds-number flows, reduction of the computational cost is considerable when using the LES/RANS hybrid methodology. The consideration of a Smagorinsky constant for a compressible flow analysis may suggest that the optimal value of Smagorinsky constant may be larger in the flows with strong compressibility than in incompressible flows.