An On-Line Data Reduction System for Photon Correlation Laser Anemometry

Photon correlation techniques have proved extremely powerful in obtaining laser anemometry data under difficult experimental conditions, especially when the scattered light levels are extremely low, but further processing is necessary to obtain explicit information about the velocity distribution in the measurement region. In this paper the various procedures based on the Fourier transform which have been developed at the Royal Aircraft Establishment in the course of a series of experiments on many types of flow, both subsonic and supersonic, will be described. In addition details of an integrated on-line data acquisition and reduction system comprising a digital correlator and a minicomputer and which is capable of yielding estimates of mean velocity and turbulence intensity will be presented. The important design features of the system will be discussed and examples of its performance in recent experiments will be given.