Correlation and Spectral Density Measurements by LDA (Laser Doppler Anemometry)

摘要

The state-of-the-art in correlation and spectral density measurements by means of laser Doppler anemometry (LDA) is reviewed. It is stressed that laser anemometry relies on the presence of particles in the flow serving as flow velocity indicators. This means that, except in heavily seeded flows, the instantaneous velocity can only be sampled at random instants. This calls for algorithms to estimate both correlation functions and power spectra. Possibilities to handle the problem of random sampling are described. It is shown that correlation methods and spectral density measurements with LDA produce information on flow characteristics which cannot be achieved by any other measuring procedure, particularly for the detection of coherent structures in flows of low turbulence and for spectra of velocity fluctuations in high temperature flows.