MIXING STUDIES OF HELIUM IN AIR AT HIGH SUPERSONIC SPEEDS

This paper presents a mixing study using gas injection at low transverse angles into M = 3 and M = 6 crossflows. Effects of injectant asymmetries on the mixing processes were also tested by including low injector yaw angles. Ambient temperature helium was injected at matched pressure conditions as well as at 5 x matched pressure into a Mach 6 freestream, with Reynolds number of 5.4 x 10(7)/m. Complementary tests at Mach 3, Re = 5.0 x 10(7)/m, were performed. The primary data are concentration measurements and meanflow measurements with nanosecond exposure shadowgraphs and surface now visualization. At Mach 6, the matched pressure injection case, as compared to the underexpanded case, was found to show a greater injectant core penetration growth rate and a greater concentration decay rate. When the Mach 6 results were compared to similar experiments with a Mach 3 freestream, only a small decrease in the downstream core penetration and mixing rates was observed. However, due to much less initial mixing near the injector at the higher Mach number, the Mach 6 results showed a longer distance for the injectant core to decay to a concentration level corresponding to the H-2-air stoichiometric ratio. Other results showed that the plume remained supersonic and that moderate total pressure losses were found. Also observed was that, for both Mach 3 and Mach 6 freestreams, injector yaw did not increase the rate of decay of the maximum concentration, but that yaw did cause an increase in the overall injectant plume cross section, thus increasing the size of the mixing region.