The Structure of the Doppler-Difference Signal and the Analysis of Its Autocorrelation Function

摘要

The Doppler-difference optical arrangement is nowadays the one most commonly used for fluid flow investigations with a laser anemometer. In this review, the essential characteristics of the Doppler-difference signal and of the associated autocorrelation function are considered for both laminar and turbulent flows. Experimental conditions under which it is known that the autocorrelation function can be analysed to yield reliable estimates of mean velocity and turbulence intensity are specified. The various data-reduction methods which have been proposed are classified and briefly reviewed. It is shown that unknown flows having relatively high levels of turbulence can only be treated successfully if there are very many fringes within a beam diameter, or if frequency-shifting techniques are used to achieve an equivalent effect. The estimation of turbulence intensity in low-turbulence flows also presents special difficulties and a procedure which uses information already available in the transform plane is described. (Author)