Turbulence Modelling for SWTBLI with Expansion Wave Interference Inside Scramjet Inlets

Abstract

An accurate prediction of the flowfield inside the scramjet inlet/isolator is crucial for a stable and reliable aerodynamic design. However, the complex phenomena such as shock wave-expansion wave interactions and shock wave-turbulent boundary layer interactions (SWTBLI) inside the isolator pose great difficulties to the computational modelling community. In the current work, a numerical investigation is carried out for a practical mixed compression scramjet inlet/isolator using the extensively validated SST k − ω turbulence model, and the numerical results are compared against the experimental data. Although the simulations qualitatively predict the overall shock structures, major discrepancies are observed in the predictions of separation region (location, shape, and size) and subsequent positions of the separation and reflected shocks: similar discrepancies are observed in the literature with various models. Analysis reveals that although the turbulence model is capable of predicting SWTBLI, this discrepancy is primarily because of the improper estimation of turbulence levels in the separation region due to upstream expansion wave interference. The predictions are significantly improved by recalibrating a model constant, called structure parameter a 1 , when its value was decreased from the standard value of 0.31 to 0.28. The reduction in a 1 is in contrast to observations in the literature where the structure parameter was suggested to be increased beyond the default value for separated high-speed flows. This behaviour is due to the expansion wave interference whose effects, opposite to that of shock, need to be incorporated into the model for accurate predictions of scramjet flows.