In its simplest form, laser Doppler velocimetry (LDV) is a technique to measure the direction and speed of fluids or air by crossing two beams of laser light in the flow of the fluid, analyzing the frequency characteristics of the reflected light from the interference pattern caused by the passing particles, and relating this frequency to the velocity of the flow using the Doppler effect. Using a variation of LDV that utilizes a fiberoptic tip probe and diffractive optics, researchers at Dresden University of Technology (Dresden, Germany) have developed what they believe is the first laser-Doppler-based method for in situ single-blade tip-clearance measurement of turbomachines that is at least a factor of two more accurate than capacitive methods.
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