Adjustment and evaluation of an LDA probe for accurate flow measurement

An LDA probe with optimized measuring volume was obtained based on repeated adjustments of a preconfigured LDA system with a calibrated spinning disc. A retriggerable pulse-width-and-time-delay module was used to trigger and freeze favorable Doppler bursts. After a repeated beam-steering procedure and a fringe-pattern analysis, we found that the variation of fringe spacing throughout the measuring volume was reduced from 3% to 0.28%, such that the adjusted probe gave more accurate measurements. To verify this applicability in velocity calibration, the fringe spacing of the adjusted LDA measuring volume was treated as a velocity coefficient, and its mean and measurement uncertainty was experimentally estimated. Analysis shows that the expanded uncertainty of the coefficient was 0.10% at the 95% level of confidence for both the components of the LDA. The results demonstrated that the adjusted LDA system was qualified to perform accurate flow measurement.