Velocity biasing of two-component LDV data in low-turbulence flows

Attention is given to a velocity biasing problem encountered in the application of two-component laser Doppler velocimetry (LDV) to low turbulence flows. The problem was noted in measurements conducted on the axis of a simple, sudden expansion pipe flow, where mean axial velocity was about 30 m/sec, when it was realized that the alignment procedure and angle measurements involved could not account for the magnitude of error obtained.