ABSTRACT
Fluid is the common name given to gas and liquid. There are various kinds of flow-velocity measurement techniques. The simplest means is to use a measuring probe such as a pitot tube or a hot-wire probe. Quantitative optical flow visualization has become an indispensable tool in the investigation of complex flow structures. Advances in laser, computer, and digital image-processing techniques have made it possible to extract quantitative flow information from visualized flow images of tracer particles. The Laser doppler velocimetry (LDV) utilizes the Doppler effect by detecting the Doppler frequency shift of laser light that has been scattered by tracer particles moving with the fluid. The basic principle of LDV measurement is the Doppler frequency shift of the scattered light from tracer particles seeded in the flow. Depending on the location of receiving optics and photodetector, collecting the scattering light, the LDV system is classified into the forward-scatter mode and the backscatter mode.
