Measurement of turbulent wall velocity gradients using cylindrical waves of laser light

A new optical instrument has been developed for direct measurement of instantaneous velocity gradients at the bounding wall. Light emerging from two tiny optical slits in the surface is used to form a "fan of fringes" in the region very near the wall. Doppler frequency of the light scatter...

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Bibliographic Details
Published in:Experiments in fluids 1991-02, Vol.10 (5), p.257-266
Main Authors: NAQWI, A. A, REYNOLDS, W. C
Format: Article
Language:English
Subjects:
Exact sciences and technology
Fluid dynamics
Fundamental areas of phenomenology (including applications)
Instrumentation for fluid dynamics
Physics
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Summary:A new optical instrument has been developed for direct measurement of instantaneous velocity gradients at the bounding wall. Light emerging from two tiny optical slits in the surface is used to form a "fan of fringes" in the region very near the wall. Doppler frequency of the light scattered by the seed particles is directly proportional to the velocity gradient. The system has been used to measure the statistics of the streamwise and spanwise velocity gradients in a turbulent boundary layer. The streamwise and spanwise rms fluctuations were found to be 38 and 11 percent of the mean streamwise value respectively. The latter result is subject to a large uncertainty. (Author)
ISSN:0723-4864
1432-1114
DOI:10.1007/bf00202458