FINITE-AMPLITUDE STANDING WAVES IN HARMONIC AND ANHARMONIC TUBES

Finite amplitude standing waves have been studied in closed tubes fill ed with air and driven by a piston at frequencies near 200 Hz. The tub es were driven at resonance generating standing waves with amplitudes of up to 160 dB re: 20 muPa. The main objective was to measure the dis sipation of energy by the fundamental frequency and the higher harmoni cs, as well as by other nonacoustic mechanisms. A formulation develope d by Coppens and Sanders [J. Acoust. Soc. Am. 58, 1133-1140 (1975)] us ing a single nonlinear equation to describe standing waves in cavities of arbitrary resonance frequencies and quality factors was used succe ssfully to predict the higher harmonics. In addition, the effect of de tuning the tubes on the energy dissipation was measured in tubes with variable cross sections. It was found that the detuned tubes effective ly suppress the energy transfer into (and energy dissipation by) the h igher harmonics. It was also found that expanding rather than contract ing the cross section of the tubes minimized the dissipation of energy through nonacoustic mechanisms.