Laser anemometry



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Laser anemometry is the newest method of measuring the velocity of fluid flow. It has several advantages over conventional types of anemometers, principally, high spatial resolution and high frequency response while having the capability of measuring up to three dimensional flow. In the laser anemometer laser light is scattered by particles in the fluid, which may be either a gas or a liquid. This scattered light is Doppler shifted in frequency by the. motion of the particles and is heterodyned with unscattered light beams on the phctocathodes of photomultiplier tubes. The frequencies of the outputs are linear combinations of the velocity components of tire scattering particles. A two-dimensional anemometer was constructed to measure mean and turbulent velocities of spherical oil droplets whose sizes range from one-half to ten micrometers. Computer programs for calculating the Mie scattering of spherical particles were developed. A detailed analysis of the optical system of the anemometer if given, and the response of the photomulripliers in terms of signal and noise is developed from theory and compared with measured results.