PHASE STEP HOLOGRAPHIC-INTERFEROMETRY APPLIED TO HYPERVELOCITY, NONEQUILIBRIUM CYLINDER FLOW

For blunt bodies the reduced bow shock wave stand-off distance and the shock layer density rise in the stagnation region as compared to idea l gas flow are phenomena caused by dissociative effects. In this work experiments with a R(BODY) = 45 mm radius cylinder and an aspect ratio of L/R(BODY) approximate to 11 are described. The tests were carried out in the High Enthalpy Shock Tunnel in Gottingen (HEG), a free pisto n driven shock tunnel. Two different test conditions at reservoir enth alpies of around 21 MJ/kg and Mach numbers of around 9 in air and nitr ogen were available. Optical measurements with a holographic phase ste p interferometer to obtain complete flow field density gradients have been carried out. By increasing the signal-to-noise ratio with the tec hnique of phase stepping over the original recording quality, high qua lity interferograms are obtained. The high spatial resolution of the h olograms results in the creation of hologram-schlieren images which ar e compared to directly recorded laser-schlieren images. Infinite and f inite fringe interferograms and the complete density fields for the tw o free-stream conditions are presented. The stagnation line densities are quantified. The measured results are shown and compared with Navie r-Stokes calculations which account for chemical reactions in the flow . The numerical code underpredicts the stand-off distance of the bow s hock wave. It is shown that the flow behind the bow shock wave is in n on-equilibrium and that it reaches equilibrium before the body for one condition.