Research of finite-amplitude acoustic pulse propagation in a thin capillary filled with a viscous-elastic fluid

Abstract

Acoustic wave propagation in a thin capillary filled with a viscous fluid is accompanied by additional attenuation because of sound energy outflow to the capillary wall due to viscous forces. It is known that a whole class of fluids exists, which change their viscous properties (shift modulus) under the applied stress. It is the so-called Bingham fluids. The results of experimental research of wide frequency band sound pulse propagation in the capillary filled with a raw oil are presented. A pulse was generated by laser radiation. The amplitude of the pulse reached up to 1 MPa and its time duration was about 20 ns. Acoustic signal reception was provided by a PVDF gage and registered by a digital oscilloscope in the frequency range of 100 MHz. Experiment shows a kind of induced ‘‘transparency’’ for the high-amplitude sound pulse propagated along a capillary of 0.4-mm radius. This effect of acoustic-induced transparency of viscous fluid shows a rapid growth of high-frequency components of the sound signal passed through the capillary with respect to the growth of laser pulse energy. Meanwhile, for the small-amplitude sound signal propagation the linear relation between laser pulse energy and sound pulse amplitude is valid. [Work is partially supported by the Russian Foundation of Basic Research (project 97-02-17789).]