Sampling techniques for accurate measurement of Reynolds stresses using Laser Doppler Anemometry

An investigation has been carried out into the number of wave cycles necess ary for accurate evaluation of Reynolds stress from Laser Doppler Anemomete r output. Reynolds stress, defined as the cross product of turbulent veloci ty fluctuations, each of which is the small difference between two larger q uantities, requires more wave cycles for accurate evaluation than has hithe rto generally been considered necessary. Laboratory tests were carried out with a two-component LDA system to investigate this. The results are compar ed with the analysis of Yanta and Smith who conducted pipe flow experiments to determine limits on sample lengths in turbulent flow. (C) 1999 Elsevier Science Ltd. All rights reserved.