Acoustic cavitation: the fluid dynamics of non-spherical bubbles

In acoustic cavitation the spatial variation and time-dependent nature of t he acoustic pressure field, whether it is a standing or propagating wave, t ogether with the presence of other bubbles, particles and boundaries produc es gradients and asymmetries in the flow field. This will inevitably lead t o non-spherical bubble behaviour, often of short duration, before break-up into smaller bubbles which may act as nuclei for the generation of further bubbles. During the collapse phase, high temperatures and pressures will oc cur in the gaseous interior of the bubble. This paper concentrates on the non-spherical bubble extension to the earlie r spherical-bubble studies for acoustic cavitation by exploiting the techni ques that had previously been used to model incompressible hydraulic cavita tion phenomena. Bubble behaviour near an oscillating boundary, jet impact a nd damage to boundaries, bubble interactions, bubble clouds and bubble beha viour near rough surfaces are considered. In many cases the key manifestati on of the asymmetry is the development of a high-speed liquid jet that pene trates the interior of the bubble. Jetting behaviour can lead to high press ures, high strain rates (of importance to break-up of macromolecules) and t oroidal bubbles, all of which can enhance mixing. In addition it may provid e a mechanism for injecting the liquid into the hot bubble interior. Many p ractical applications such as cleaning, enhanced rates of chemical reaction s, luminescence and novel metallurgical processes may be associated with th is phenomenon.