Correcting Spectral Density of Laser Doppler Anemometer Signals during Measuring of High-Speed Aerodynamic Flows. Part 2

A method has been developed for constructing correction factors to compensate for distortions introduced by non-uniform frequency characteristics of the electronic path of a laser Doppler velocimeter into the spectral density of Doppler signals. The method relies on averaging a statistical ensemble of spectral densities of noise signals obtained during illumination of a photodetector with a reference white light source, constructing the inverse function to the resulting averaged spectral density with truncation in the low- and high-frequency bands, and applying digital low-pass filtering to it. In the first part, a model numerical experiment was carried out. The gas flow velocity at the Vitoshinsky nozzle exit was measured with a laser Doppler anemometer in high-velocity modes. It has been shown that in high-velocity modes (200 m/s), the application of correction factors to the spectral density of Doppler signals allows estimating the average flow velocity with an error of no more than 5%, while calculating velocities without preliminary correction of the spectral density leads to statistical measurement errors of more than 100%.