The Study Of Ultrasonic Cavitation Effects On Rigid Wall

With the development of science and technology, ultrasonic application is becoming more and more widespread in recent years. Except the traditional ultrasonic cleaning and measuring, ultrasonic application develops very quickly too in the machinery, the medical service, the chemical industry, national defense and so on. It has received the very big value especially in the medical treatment., for example the HIFU technology, the ultrasonic treatment tumor, the ultrasonic treatment blood vessel of brain disease and so on. But cavitation, the mechanism of ultrasonic application, is not still clear. The mechanical effect of cavitation is studied in this article when a cavitation bubble collapses near rigid boundary.Bubble dynamics and numerical calculation method is used in this article. First, employing the bubble dynamics the Rayleigh equation is derived in the incompressible liquid, including surface tension and radiation of sound. Then the equation is solved using Runge-Kutta method in different initial radius of cavitation bubble. The result indicated that, the initial size of cavitation bubble is very important to the intensity when bubble grows and collapses. It is hard to collapse when the bubble size is too bigger to the resonate bubble of sound wave, this is stable state cavitation. The other way round, the bubble is easy to collapse and called transient state cavitation.After solving the bubble radius change rule, the velocity of the bubble growth and the collapse process is gained using numerical differential coefficient method. Then the intensity of pressure of bubble periphery is calculated with the theoretical hydrodynamics in the different initial radius bubble when bubble grows and collapses. The computed result indicated: a very small low pressure spherical shell will be formed in the process of the cavitation bubble growth and collapse regardless of cavitation bubble size.Then the collapse process of different initial radius single bubble near rigid wall is studied. The flow field of this bubble collapse near rigid wall is derived with the mirror image and the potential profile flow function method. Last the pressure in the rigid wall is derived employing Bernoulli equation. The computed result indicated: a single cavitation bubble collapses near rigid wall, leading to the change of intensity of pressure. There will be a low pressure ring in the rigid wall. This ring leads to shock wave in the wall. The intensity of pressure is stronger in the rigid wall when cavitation bubble collapse than growth. That is to say that cavitation effect will appear when cavitation bubble collapses.The process of three cavitation bubbles collapsing near rigid wall is studied in the same way with single bubble. The difference is the potential profile flow function. It is researched in case of a larger distance between bubbles and not calculating the affect each other. It is supposed that three cavitations is same, namely same size, same radius, with phase. The conclusion indicated that three bubbles collapse near rigid wall leading to the same effect that the wall receives as single bubble. Difference is that it is more intense effect when three bubbles collapse in the similar condition. Similarly, the different initial size cavitation bubbles lead to different effects that rigid wall receive. Along with radius of three cavitations bubbles reducing, the intensity of pressure to rigid wall is strengthened gradually.