Propagation of intense acoustic pulses with shocks in relaxing fluids

Abstract

The propagation of intense waves in liquids or gases with relaxation processes is a classical problem of nonlinear acoustics. The presence of relaxing processes influences acoustic propagation by changing the absorption law and introducing dispersion. The effect of the relaxation is of particular interest for short acoustic pulses, when the duration of pulse is of the same order as the characteristic relaxation time. Even for the case of linear acoustics, relaxation will compromise pulse shape. For intense waves, nonlinear effects result in additional pulse distortion, shock formation, and nonlinear energy attenuation. The propagation of intense acoustic pulses containing shocks is studied theoretically and experimentally. Two numerical simulations, a modified spectral method and a time-domain method, are used to model shock propagation. Propagation curves for waveform distortion, shock amplitude behavior, and energy dissipation are presented. Experiments are performed in acetic acid as a monorelaxing medium. Short acoustic pulses are excited by a pulsed laser. Theoretical and experimental results are in a good agreement. [Work supported by NIH, FIRCA, and RFBR.]