EFFECTS OF NONLINEARITY IN DEVELOPMENT OF ACOUSTIC STREAMING

Development of acoustic streaming generated along the beam axis of ultrasound in unbounded medium is discussed using a numerical analysis. Acoustic nonlinearity changes the distribution of driving force of streaming. If fluid-dynamic nonlinearity is neglected, the streaming velocity essentially increases in proportion to the square of source amplitude. Incorporation of acoustic nonlinearity enhances the streaming velocity near the sound source and suppresses it at a farther distance compared to the acoustically linear case. When fluid-dynamic nonlinearity is taken into account, the fundamental trend in the increase of streaming velocity changes from the second power of the source amplitude toward the first power. Thus the fluid-dynamic nonlinearity delays the development of acoustic streaming.