Effects of Rarefaction on the Shock Wave/Shock Wave Interaction in Hypersonic Regime

In a former paper by the present author, the effects of rarefaction were evaluated on the Shock Wave/Boundary Layer Interaction, in hypersonic, low density flow. The flow field on a flat plate, on which an external, oblique shock wave impinges, was simulated by the direct simulation Monte Carlo code DS2V. The test conditions were those that should be met by the Italian Flight Test Bed (FTB-X) vehicle along the re-entry path in the altitude interval 55-75 km. The study was carried out as a function of altitude in order to quantify the effects of both rarefaction and Mach number, or intensity of the shock wave, on: extension of the interaction region, heat flux, aerodynamic load, slip velocity, slip temperature. As expected, the extension of the interaction region increased with rarefaction. The maximum values of heat flux and aerodynamic load in the interaction region were about one order of magnitude higher than the same quantities without shock wave impingement and were even comparable with those on the flat plate leading edge. In the present paper, that can be considered as a logical extension of the above mentioned paper, the effects of rarefaction are quantified on the Shock Wave/Shock Wave Interaction. More specifically, the experimental apparatus in the hypersonic wind tunnel R5Ch at Office National d’Etude et de Recherches Aérospatiales (ONERA) is simulated by DS2V. This apparatus is made up of a wedge generating an oblique shock wave impinging on a bow shock generated by a circular cylinder with axis normal to the free stream. The test conditions are those already used in the above mentioned paper. These conditions are such that the Edney’s “type IV” interaction is produced. This type of interactions is the most severe shock wave/shock wave interaction. The increases of heat flux and pressure produced by interaction, with respect to the case with no interaction, range from 1.8 to 7.3 and from 2.5 to 7.8 in the above mentioned altitude interval, respectively. These increases are lower than those produced by the Shock Wave/Boundary Layer Interaction on the flat plate, using the same free stream conditions and the same wedge angle generating the oblique shock wave; those increases ranged from 5.9 to 11.8 and from 8.9 to 18.1, respectively. The extension of the interaction region, as a function of the free stream parameters, has been quantified and the effects of wall catalyticity have been also evaluated.