Heat Transfer on a Hypersonic Sphere with Diffuse Rarefied-Gas Injection

摘要

The influence of the blowing parameter (the ratio of outgas mass flux to upstream mass flux) and the rarefaction factor (Knudsen number) on the flow structure about a sphere has been studied for hypersonic flow of air. It has been found that at transitional flow conditions (K n_(∞,R) = 0.0163), when the mass-air-injection rate equals 0.7 of the freestream mass flux, the viscous layer is blown completely off the surface, and the heat transfer is zero. The displacement effect of blowing spreads both in the counterflow direction and along the surface. This effect is more pronounced at lower values of the Knudsen number K n_(∞,R) < 0.075. The width of the injection-influenced displacement zone (s / R)_(max) (at G_w = 0.94) increases by the factor of 3 at decreasing the Knudsen number from 1.5 to 0.016. The temperature contours are disturbed more significantly for helium injection than in the case of air-to-air blowing. Even at moderate helium mass blowing rates (0.7 > G_w > 0.32), diffuse outgas flow displaces completely the viscous layer off the sphere surface.