Use of Burst-Triggered Correlation for Laser Anemometry Measurements in Turbomachinery

摘要

The application of burst-triggered correlation to the processing of laser Doppler anemometry signals measured in rotating turbomachinery is described. The constraints imposed by measurements of high speed flows close to walls favor the use of laser transit anemometry. However, for applications in which a high data rate is required from flows with turbulence levels up to 25 percent, a two component Doppler-difference anemometer with a very good flare rejection capability was developed. It is possible to improve significantly the signal to noise by exploiting the transiently high rate of photon arrivals associated with light scattered from a particle rapidly transiting a small probe volume. Conditional correlation of only those signals which are significantly bunched within a time window comparable to a beam transit, provides a powerful method of enhancing the discrimination of particle signals from flare noise. A dual channel correlator was fitted with two fast preprocessor input boards which provide a burst detection capability for conditionally loading the parallel correlator channels with their respective time-expanded pulse trains. Tests show a strong motivation to exploit the individual event detection capability of burst processing, rather than simply time integrating in the correlator.