Motion of a particle in a shock-induced flow

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In order to clarify the motion of a particle in a shock-induced flow, the drag coefficient of an accelerating sphere is evaluated by measuring the mean velocity and acceleration of a moving sphere behind a planar shock propagating in a shock tube. In the experiment, the trajectories of the spheres were recorded by a multi-exposure photography. The drag coefficients were then estimated from the trajectories.The relative Reynolds numbers around the moving spheres were in a range from 10^3 to 10^5. The obtained drag coefficients were found to be higher than those from the standard drag curve by 20% on the average. Fitting a curve to the present experimental points in the range of the relative Reynolds number (Re) from 3*10^3 to 10^5 results in the following correlation for the drag coefficient, C_D,C_D=0.35+0.04log_<10>Re.The initial mechanism of a particle's lift-up by a shock passage was also analyzed experimentally. The measured rotating rate of particles revealed that particle's initial rotation is not so effective for a particle to rise up.