Computation of the flow structure of an hydrogen/air mixture downstream of a steady system of shock waves

Abstract

This paper deals with the analysis of the flow structure when a supersonic air-hydrogen mixture encounters a deflection ramp. We are interested in the conditions of a deflection, a normal reflection, or a Mach reflection, involving a portion of a curved quasi-normal shock wave. Behind this last shock, due to the rise of temperature, one may expect combustion to be stabilized. To conduct the analysis, we first determine the physical state of the flow by computing-exposant the “deflected-shock” and “reflected-shock” polars, the deflection angle and the incident Mach number being given. These polars are computed in both cases, assuming no or complete combustion behind the shock, and taking into account two models for the enthalpy of the gas mixture (affine function of the temperature or a fifth-degree polynomial of the temperature). We thus show that the combustion effects cannot be neglected when predicting the structure of the flow and the ignition lengths, and that the realistic model leads to highly diverging quantitative results, in comparison with the usual simplified model. For a given configuration, we have made the complete calculation of the Mach reflection. It should be noted that, in this particular case, a “very hot” region is observed near the point where the 3 shocks meet, region where the temperature is significantly higher than in the portion behind the normal shock.