Laser Doppler Anemometry (LDA) signal triggering and effective particle size range

The influence of laser Doppler anemometer (LDA) signal triggering on the resultant LDA-information is discussed. It is shown that for highly turbulent flow configurations the triggering of the high pass filtered LDA-signal delivers the most exact flow information, since mainly small particles contribute to the resultant LDA-information. These particles show a minimum slip and a maximum ability to follow high, frequent, flow fluctuations. It is proved that triggering of unfiltered LDA-signals is not practical for data evaluation since the resultant LDA-information is dominated by bigger particles suspended in the flow. Triggering based on unfiltered LDA-signals, furthermore, uses the particle size distribution in the flow very ineffectively, i.e., results in low data rates, despite the existence of many small particles.