Dynamics of Plumes Generated by Local Injection of Ablated Material

Abstract

Numerical modeling is employed to study the heat transfer modulation between the thermal protection shield and the gas flow that is caused by ejection of underexpanded pyrolysis gases through the cracks in the thermal protection shield. The simulations are performed for an axisymmetric bluff body flying at Mach 7. The influence of the geometry of the thermal protection shield on the heat transfer pattern is studied for two representative shapes. The results are presented for three different flight altitudes (low, ground level; moderate, 20 km; and high, 30 km). At the low altitude, the plume pressure is lower than the pressure behind the detached front shock wave and the plume propagates slowly along the wall surface. At high and moderate altitudes, the plume path (and, consequently, the convective heat transfer between the thermal protection shield and the plume) depends on the plume interaction with the bow shock wave. The effect of viscosity for the plume injection conditions and freestream Mach number considered is found to be negligible at simulated altitudes. The effect of the initial pressure of pyrolysis gas on the plume dynamics is significant. The presence of the blast wave associated with the underexpanded plume alters the heat transfer and increases mixing. Finally, the enhanced heat transfer caused by the emergence of multiple plumes is investigated.