A preliminary investigation of high amplitude standing waves with laser Doppler anemometry

Abstract

A previous study of thermoacoustic heat transport phenomena Atchley et al., J. Acoust. Soc. Am. 88, 251-263 (1990) reported measurements of the acoustically induced temperature difference AT generated across short, poorly thermally conducting plates situated in high amplitude acoustic standing waves. That study focused on the dependence of AT on the position of the plates in the standing wave, the mean gas pressure and acoustic pressure amplitude. For a given mean gas pressure, there was a threshold acoustic pressure amplitude above which irregularities appeared in the plots of AT vs kx. There was evidence that some velocity-dependent effect might be the cause of the discrepancies. An investigation of the acoustic velocity field in high amplitude standing waves has been initiated to determine whether there are measurable irregularities in the velocity field that can account for the observed behavior. The use of Laser Doppler Anemometry (LDA) provided accurate measurements of the velocity behavior of a gas in an empty resonator, as well as in a resonator with a crude thermoacoustic stack. Preliminary results are reported. The major conclusions are that LDA measurements of acoustic velocity fields provide reliable results and there are no significant velocity perturbations evident in our measurements. A videotape of acoustically induced flow in the resonator with a stack indicate that significant velocity perturbations do exist on time scales other than acoustic.