Fluid flow measurements using a scanning laser Doppler vibrometer

摘要

The laser Doppler vibrometer (LDV) is an instrument based on a heterodyne interferometer that can be used to measure vibrations at a location on a structure. By moving the laser beam using scanning mirrors a full field vibration measurement can be performed. While the main purpose of the scanning LDV is to measure vibrations, recently several authors proposed to use the LDV for flow and sound measurements. The idea is to aim the laser vibrometer at a rigid block. When a pressure field is present between the LDV head and the rigid block this will result in changes of the refraction index that are related to the measured Doppler shift. Because no seeding particles are needed, the method opens new opportunities to measure phenomena that were previously difficult to measure. Unfortunately, the current LDV measurement techniques are only able to measure dynamic flow fields (both turbulent and coherent).