Velocity Distributions of Sphere Wakes

Abstract

The present report is concerned with the wake velocity results measured in sphere wakes with the sequential spark technique. This technique has been employed to measure the radial distribution of velocity in the turbulent wakes of spheres flown at Mach numbers from 3.5 to 13 and at Reynolds numbers from 0.2 × 106 to 106 over a range of axial distance extending up to 3500 diam. For each selected combination of velocity, pressure, sphere diameter, and axial distance, a sufficient number of firings have been observed so as to permit the statistically meaningful determination of the mean profile of velocity. On 14 500 ft/s spheres, wake velocity mean characteristics were determined for ambient P∞D (pressure times sphere diameter) values of 20, 40, and 100 Torr-in. The results showed only a weak dependence of the wake velocity on P∞D. Measurements were also made at sphere velocities of 9000 and 4000 ft/s at a P∞D value of 100 Torr-in. The measurements revealed a strong influence of the Mach number on the wake velocity in the intermediate region of the wake. One of the important findings, observed under all the test conditions, is that the radial distribution of mean axial velocity in the turbulent wake is well approximated by a Gaussian curve.