Heat flux characteristics within and outside a forward facing cavity in a hypersonic flow

Abstract

A forward facing cavity effect on heat flux variations inside the cavity and over the nose surface is studied over a typical projectile geometry using the shock tunnel experiments. The flow oscillation will tend to oscillate the shock, which in turn varies the heat flux over the nose surface as well as inside the cavity. The higher length to diameter (L/D) ratio of the cavity plays an important role in nose surface heat flux reduction and investigated for L/D = 1, 2 and 3 by a uniquely designed model. The cavity flow oscillation period is determined, using the base pressure and surface heat transfer signals measured inside the cavity with reference to the pitot probe steady test time and shock oscillation period. The frequency analysis for oscillations is performed using the fast Fourier transformation. Experimental results showed that, the mean nose surface heat flux reduced by ≈4.6% to ≈7%, ≈6% to ≈8% and 3% to ≈31.4 and the mean shock standoff distance (l) is increased by ≈13%, ≈25% and ≈35% for L/D = 1, 2 and 3 configurations respectively with reference to the baseline geometry (without cavity geometry). As L/D increases, the nose surface location on which the heat flux reduction is observed moves towards the cavity lip and more surface area is covered with lower heat flux. Cavity region heat flux variations are studied by incorporating the thin film sensors over the cavity surface and it is observed that, a significant ≈32.5% to ≈36%, and ≈28% to ≈58% lower mean heat flux for L/D = 2 and 3 respectively with reference to the baseline geometry stagnation point heat flux.