An Optical Boundary-Layer Probe

Abstract

The applicabilh^ of the schlieren-photomultiplier technique to obtain quantitative density measurements in the laminar boundary layer induced by a traveling shock wave in a shock tube is investigated. Tests were conducted at a Mach number of 1.58 so that the data could be compared with the exact theoretical solution tabulated by Mirels. The data obtained are in good agreement with the theory if the distance of the light beam above the floor of the shock tube is adjusted to fit the theoretical curve; this would not be necessary if a larger shock tube were used. Values of the transition Reynolds number were also determined which are slightly less than those found by Martin using an interferometer. I t is shown that this technique is sensitive enough to detect changes in density that are only 0.006 per cent of atmospheric density.