Method of measuring velocity gradients in a flowing medium and a

Details Method of measuring velocity gradients in a flowing medium and a Method of measuring velocity gradients in a flowing medium and a

1983-03-28

1986-02-25

Buczinski, S. C.

Optics: measuring and testing

Velocity or velocity/height measuring

With light detector

356342, G01P 336

Patent

active

045726647

ABSTRACT:
In a method of measuring velocity gradients in a sample volume (2) in a flowing medium, by which method radiation scattered by particles entrained by the medium and irradiated by spatially coherent electromagnetic radiation, in particular laser light, is detected and measured and the difference in Doppler shift in the radiation from different particles in the sample volume (2) used as a measure of the velocity gradient, an optical element (3) is inserted in the radiation path from particles in the sample volume (2) to the detector (4). The optical element (3) has such properties that essentially only radiation scattered simultaneously from particle pairs in the sample volume (2) spaced apart a distance determined by the optical element (3) are made part of the measuring signals to be combined to form the signal which is a measure of the difference in the Doppler shifts and thereby of the velocity gradient in the sample volume (2) defined by the measurement points.
The optical element (3) may for example be an optical grating of the absorption, phase or reflection type or intermediate forms, a birefringent element, a Bragg cell, a combination of a totally reflective surface and a beam splitter or possibly a glass plate having one of its surfaces coated with a totally reflective material.
The apparatus comprises a source for electromagnetic radiation (1), a detector (4) for receiving radiation scattered from particles in a sample volume (2), means for recording the output signals from the detector (4) and an optical element (3) of the above-mentioned type defining the position of a relevant particle pair.

REFERENCES:
patent: 3547540 (1970-12-01), Shigemoto
J. W. Foreman et al., IEE Journal of Quantum Electronics, Aug. 1966, pp. 260-266.
F. Durst et al., Principles and Practice of Laser Doppler Anemometry, 1981, pp. 79, 83.

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