Standing wave analysis of the low amplitude performance of a thermoacoustic prime mover.

Abstract

A standing wave analysis of the low-amplitude performance of a thermoacoustic prime mover is presented. The analysis, motivated by Swift [G. W. Swift, J. Acoust. Soc. Am. 84, 1145–1180 (1988)], assumes that the acoustic pressure and velocity can be described in terms of a standing wave throughout the prime mover. The analysis is not limited by either the small boundary layer or short stack approximations. The results of the analysis are compared to measurements of the quality factor Q of a prime mover both below and above onset. Measurements were made in both a helium- and an argon-filled prime mover for mean pressures ranging from approximately 80 to 500 kPa. Below onset the Q is determined from the frequency response of the prime mover. Above onset the Q is determined from the initial rise time of the acoustic oscillations. In general, the agreement is good, indicating that previous work on finite amplitude standing waves [A. B. Coppens and J. V. Sanders, J. Acoust. Soc. Am. 58, 1133–1140 (1975)] can, perhaps, be used to explain the observed high-amplitude waveforms in prime movers. [Work supported by ONR and the NPS Res. Prog.]