Velocity Bias Associated With Laser Doppler Anemometer Controlled Processors

The controlled processor has been proposed as a means of avoiding velocity bias in laser Doppler anemometry. A theoretical model is presented to show that results free of bias can be obtained if both the ratio of integral time scale to measurement time scale (integral scale data density) and the ratio of sampling time to the measurement time scale (normalized sample interval) are greater than five. Further, by separation of the integral scale data density and normalized sample interval parameters, it is shown that at any integral scale data density the controlled processor will not produce any less bias than a sample and hold processor and no more bias than the free running (unweighted) processor. In some situations it may be considered superior to the sample and hold processor as the data processing and hardware requirements are reduced without any loss of measurement accuracy. Experimental data confirming the theoretical results are also shown. Some of these data are contrary to at least one model available in the literature.