EFFECTS OF NONLINEARITY IN DEVELOPMENT OF ACOUSTIC STREAMING

Development of acoustic streaming generated along the beam axis of ult rasound in unbounded medium is discussed using a numerical analysis. A coustic nonlinearity changes the distribution of driving force of stre aming. If fluid-dynamic nonlinearity is neglected, the streaming veloc ity essentially increases in proportion to the square of source amplit ude. Incorporation of acoustic nonlinearity enhances the streaming vel ocity near the sound source and suppresses it at a farther distance co mpared to the acoustically linear case. When fluid-dynamic nonlinearit y is taken into account, the fundamental trend in the increase of stre aming velocity changes from the second power of the source amplitude t oward the first power. Thus the fluid-dynamic nonlinearity delays the development of acoustic streaming.