Measurement of shock standoff distance for sphere in ballistic range

The shack standoff distance for a sphere is measured in a ballistic range i n the intermediate hypersonic regime. The measurement is made for hemispher es of nose radius of 7, 14, and 15 mm, flight speeds between 2.44 and 3.85 km/s, and ambient pressures between 5.6 x 10(2) and 2.0 x 10(4) Pa. The sho ck waves and flowfields over the spheres are visualized by shadowgraph or s chlieren method using a pulse Nd-YAG laser as light source. The effect of c ontamination in the test air on the standoff distance was examined by using a turbo-molecular pump in setting the initial gas pressure. Shock standoff distances vary with the ambient pressure. Its variation from those in the ideal gas analysis clearly demonstrates the effect of the thermochemical no nequilibrium. The data are compared with the results of the previous invest igation. The present data showed slightly larger standoff distance than tho se of previous experiment, indicating the effect of test gas contamination.