Ultrasonic waves were sent through the wakes of circular cylinders of certain simple profiles and of plates in air flow. By application of multichannel pulse-height analysis, probability density distributions of the sound-wave phase fluctuations (“phase spectra”) were measured. One gets Gaussian distributions in cases of purely turbulent flow and characteristically shaped curves (most often with two maxima), if, additionally, the wake flow contains discrete vortices. The computer-aided evaluation of the phase spectra allows, simultaneously, determination of the magnitude of the turbulent motion in direction of the sound-wave propagation and the circulation of the vortices and, furthermore, leads to information about the general structure of the flow.
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Schmidt et al. (1970) studied this question.