Application of the laser gradient anemometer (LGA) for fluid flow measurements

Measurements of fluid velocity gradients by ordinary laser Doppler anemometry are subject to many biasing effects. A new optical measurement technique, laser gradient anemometry, is proposed, in which the frequency shifts of laser light scattered by two different particles (instead of one, as in laser Doppler anemometry) are obtained. The method is based on mixing light scattered by two particles with relative separation defined by an optical filter. The experimental setup is changeable to give the velocity gradient in various directions and for various components. Results on the velocity gradient measurements for a rotating perspex disc and a cylindrical flow are given.