Motion of tracer particles in supersonic flows

Factors that may act on particle motion in high-speed flow are investigated. The classical expressions of drag coefficient C-D for a sphere are reviewed. Then, a drag expression is proposed, extending Cunningham's method to higher velocities and Knudsen numbers. This law, valid from continuum to free molecule conditions, for Re less than or similar to 200 and M less than or similar to 1 (where Re and M are, respectively, the Reynolds and Mach numbers based on relative velocity), is used to compare calculated and experimental values of the drag coefficient, as well as the particle velocities across an oblique shock wave. Calculated results are found to be in agreement with experiments.