Fluid dynamics phenomena induced by power ultrasounds

Propagation of power ultrasound (from 20 to 800 kHz) through a liquid insid e a cylindrical reactor initiates acoustic cavitation and also fluid dynami cs phenomena such as free surface deformation, convection, acoustic streami ng, etc. Mathematical modelling is performed as a new approach to predict where acti ve bubbles are and how intense cavitation is. A calculation based on fluid dynamics equations is undertaken using computational fluid dynamics code; t his is of great interest because such code provides not only the pressure f ield but also velocity and temperature fields. The link between the acousti c pressure and the cavitation field is clearly established. Moreover, the p ressure profile near a free surface allows one to predict the shape of the acoustic fountain. The influence of the acoustic fountain on the wave propa gation is shown to be important. The convective flow inside a reactor is numerically obtained and agrees wel l with particle image velocity measurements. Nonlinearities arising from th e dissipation of the acoustic wave are computed and lead to the calculation of the acoustic streaming. The superimposed velocity field (convective flo w and acoustic streaming) succeeds in simulating the bubble behaviour at 50 0 kHz, for instance. (C) 2000 Elsevier Science B.V. All rights reserved.