Evaluation of Turbulence Modeling in Supersonic Afterbody Computations

The numerical simulations of supersonic afterbody flows performed by current RANSE solvers do not still provide satisfactory results, since the base drag is generally overpredicted. It is a common belief that the inadequate modeling of turbulent phenomena, occurring in the separated regions downstream the rear part of body, is the main reason for these mispredictions. In this framework, the present paper proves that the compressibility effects on turbulence are responsible of the underprediction of the base pressure. This finding has been confirmed by numerical simulations. Specifically, supersonic backward-facing step flows at different shoulder Mach numbers (Ms = 1.1-3.39) and an overexpanded flow in an aerospike nozzle have been computed using both the basic Spalart-Allmaras model and a corrected version accounting for the compressibility. The comparison of numerical results with experimental data displays that the application of the modeling of the compressibility effects improves significantly the prediction of the average base pressure in all considered test cases.