| 摘要 |
A method of measuring the flow velocity in wind tunnels is indicated, in which a path covered by particles located in a flow is employed as a measure of the flow velocity. In a pre-determined time interval, the particles are illuminated twice in a plane by means of a light, and a light reflected by the particles is recorded and transmitted in the form of an image. The image is transilluminated by a second coherent light beam focused in a first Fourier plane, and in this way a first Fourier-transformed image is produced, which is recorded in its turn. The image and the first Fourier-transformed image (23) are displayed immediately. The first Fourier-transformed image (23) is transilluminated by a third coherent light beam (19), and consequently a second Fourier-transformed image (34) is produced in a second Fourier plane (33) in an optical manner. The second Fourier-transformed image (34) is recorded and immediately further processed.
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