Sphere Drag in a Low Density Supersonic Flow

Sphere drag coefficients were measured in the Berkeley Low Density Wind Tunnel at Mach equals 2, 4, and 6, and free stream Reynolds numbers between 10 and 10,000 for both insulated and cold wall conditions. The measurements indicate that sphere drag in this regime is strongly dependent on the Reynolds number behind a normal shock wave, and only weakly dependent on Mach number. In addition, it was found that a decrease in wall temperature/stagnation temperature (T sub w/T sub o) from 1 to 0.26 was accompanied by a 5 - 10% decrease in the drag coefficient. A precision microbalance was used to obtain data for insulated spheres, and a moving model technique was used to obtain data for small spheres falling freely through a wind tunnel jet. These latter tests were performed using both cold and insulated models. The results on insulated spheres at M equal 2 and 4 were in good agreement with the measurements of other investigators. The results of the cold wall tests indicate that for Mach numbers greater than 5 in air, sphere drag coefficients are a function only of T sub w/T sub o and the post normal shock Reynolds number. (Author).