The design and performance of a laser Doppler velocimeter (LDV) used in a turbulent water-overice convection experiment are described. The LDV was operated in a reference beam mode with an ultrasonic diffraction grating shifting the reference beam frequency to provide bipolar sensing of the vertical velocity, and a phase-locked loop was used to demodulate the Doppler frequency information. The maximum observed velocities in the experiment were ± 1 mm/sec, and the accuracy of instantaneous measurement was limited by Brownian motion and laser line width to ± .04 mm/sec for a 2 Hz frequency response. The practical difficulties encountered in this system are discussed, and typical results are presented. In particular, it was found that when the photocurrent signal-to-noise ratio was low, the relation between the velocity and the frequency demodulated output exhibited a severe loss in sensitivity. An analysis of this effect is given for LDV systems utilizing high scattering particle concentrations, from which an equation relating the sensitivity loss to the signal-to-noise ratio is derived.
Adrian, R. J., "LDV Measurements in Turbulent Free Convection" (1973). Symposia on Turbulence in Liquids. 108.
3rd Biennial Symposium on Turbulence in Liquids (1973: Sep., Rolla, MO)
Chemical and Biochemical Engineering
Article - Conference proceedings
© 1973 University of Missouri--Rolla, All rights reserved.