Acoustic Streaming Resulting from Localized Vibratory Excitation of a Membrane

Abstract

It was reported previously [Elder, Kolb, and Nyborg, J. Acoust. Soc. Am. 26, 933(A) (1954)] that if a membrane bounding a liquid is caused to vibrate in a localized region the fluid adjacent to it will be set into steady vortex motion. One simple way to realize this situation is to bring a vibrating metal tip of circular cross section into contact from below with a membrane which supports a small body of liquid. A characteristic (axially symmetric) vortex motion then takes place near the tip in the liquid above, as may be seen by observation with a microscope and by use of indicating particles. Particularly high accelerations and velocities exist in a ring near the tip periphery. Streaming phenomena of this kind have now been observed under a variety of situations, at frequencies varying from 100 to 40 000 cps. Because of the associated convection and viscous stress such streaming is an important secondary cause of sonic irradiation effects. Sketches and photographs of streaming patterns will be shown, and theory for the motion discussed. [Supported in part by grant RG-4431 from the National Institutes of Health.]