ASA 125th Meeting Ottawa 1993 May

4aPA9. The effect of compressibility on acoustical streaming near rigid boundaries.

Quan Qi

Dept. of Theor. and Appl. Mech., Univ. of Illinois at Urbana--Champaign, Urbana, IL 61801

The effect of compressibility on acoustic streaming near rigid boundaries is discussed for plane traveling, as well as, for plane standing waves. The investigation is motivated by the fact that neglecting compressibility in the study of acoustic streaming near a rigid boundary lead to an incomplete description of the streaming velocity field both inside and outside the boundary layer. It is shown that an improved description may be obtained by including the effect of compressibility in the analysis of flow field in the viscous-acoustic boundary layer. The resulting acoustical streaming velocity outside the boundary layer is shown to depend not only on the amplitude of the primary wave, but also on the Prandtl number and the ratio of the specific heat of the fluid medium. Calculations based on typical numerical data suggest that the streaming velocity outside the boundary layer is larger than the classical results obtained with the incompressible fluid assumption. Relevance to the on-going study of ultrasonic cleaning will also be briefly mentioned. [Work supported by the Hunt Fellowship.]