Turbulent Flow Simulations for Hypersonic Intakes
The aerodynamic design of hypersonic inlets is a critical issue for the overall performance of an air breathing propulsion system. The primary purpose of the inlet is to provide homogeneous high–pressure flow to the engine with a minimum of aerodynamic losses. Compression is performed through a series of oblique shock waves and internal contraction that lead to a shock wave/expansion wave interaction pattern inside the inlet. Two phenomena characterize the technological problems of the inlet: on the one hand, the interaction of strong shock waves with thick hypersonic boundary layers causes large separation zones that reduce the captured mass flow and thus the engine performance. On the other hand, the high total enthalpy of the flow leads to severe aerodynamic heating, further enhanced by turbulent heat fluxes.
For what concerns the simulation of wall dominated flows with thick boundary–layers, strong shock / boundary–layer interaction and with separation, as they are of interest here, the assumption of a linear dependence between the Reynolds stress tensor and the strain rate tensor, as in eddy viscosity models, is not always valid. Therefore, differential Reynolds stress models (RSM) are important. Those models solve transport equations for each component of the Reynolds stress tensor as well as for an additional length scale. Thus, they are computationally expensive. Furthermore, they decrease the stability of the numerical scheme.
Nevertheless the combination of an adaptive code and a RSM for turbulence are now under investigation since they are expected to give good results in the study of the flows of interest here. In the future the performance of the RSM might be enhanced when connected to a transition model and taking into account high temperature gas dynamics.