Optimized Numerical Simulation Of Acoustic Cavitation

With the development of science and technology, ultrasound is applied more and more widespread. In addition to traditional ultrasonic cleaning and ultrasonic measuring, in machinery, medical, chemical, defense and other fields, ultrasonic application also develops very rapidly and many new results have emerged. Particularly in recent years, in the medical field ultrasound applications received considerable attention, such as HIFU technology, ultrasound in the treatment of tumors, ultrasound in the treatment of cerebral vascular disease. And a lot of ultrasonic cavitation is an important mechanism of ultrasound. However, due to many factors, ultrasound of this important mechanism - Ultrasonic cavitation is still a unresolved problem. This article has been studied how to optimize the ultrasonic cavitation effect, which is how to control the effects of ultrasonic cavitation extent-cavitation intensity, in order to reveal the mechanism of the application of ultrasonic cavitation.First, this paper summarizes the previous research on ultrasonic cavitation, as well as some developments of the current research, and sums up the acoustic cavitation applications in various fields.Then this article also introduces the acoustic the basic knowledge and theory on cavitation, and sums up the previous measurement methods of acoustic cavitation intensity.Then, this paper, study the mechanism of optimizing the acoustic cavitation theoretical which numerical calculation method. First of all, based on the bubble dynamics, the Rayleigh equation is derived in the incompressible viscous fluid considering sound radiation and the surface tension of the fluid. Then it is solved with Runge-Kutta method, in particular, on various parameters to solve the cavitation bubble's movement. The results show that: the initial radius of cavitation bubble size, acoustic frequency, sound intensity, sound field and other factors in the cavitation bubble growth and collapse play a decisive role in the process. Compared with the acoustic resonance bubbles, larger bubbles in acoustic cavitation fields would be very difficult to collapse, which is called the steady-state cavitation bubble; in contrast smaller bubbles in acoustic cavitation would be easy to collapse, which is called transient cavitation bubble; for single-frequency sound, the higher the sound frequency is, the more difficult the acoustic cavitation becomes; transient cavitation will occur only when the sound intensity is more than the cavitation threshold, and when the sound intensity is less than cavitation threshold, no matter how other parameters change the collapse of the bubble would not occur, and in some certain context, the greater the sound intensity is, the more intense acoustic cavitation is, while in other certain scope, with the sound intensity increasing, the acoustic cavitation becomes weaker; for the sound field, the sound pressure thresholds of the mixed sound field are smaller than those of the traveling-wave sound field, and therefore it is easier to produce cavitation in the mixed sound field and acoustic cavitation generated by bi-frequency sound field is more than that generated by the single-frequency. There are good experimental proofs when the frequency is right, the acoustic cavitation generated by the bi-frequency sound field is more than that generated by two separate single-frequency sound fields. And the above experimental results have proved. At the same time, such factors as environmental pressures, liquid viscosity, surface tension, inner air pressure, the bubble gas type, temperature and so on also have different impacts on the acoustic cavitation to some degree. With the increasing environmental pressure, the amplitude of the bubble decreases gradually, and cavitation weakens to some extent, but there is little change in amplitude in certain scope; when the liquid viscosity increases, the amplitude of the bubble decreases and cavitation threshold increases, and therefore cavitation intensity weakens, but when the collapse occurs cavitation is intense, and therefore it has less impact on cavitation; with the increasing liquid surface tension, the amplitude of air bubble in the expansion phase of sound wave decreases, but the amplitude of air bubble in the in compression phase of sound wave increases because the total pressure in the bubble increases, in general, liquid surface tension has a less impact on the amplitude of the bubble; With the increasing bubble pressure, the amplitude of bubble in expansion phase of sound wave increases, but the amplitude of bubble in the compression phase of sound decreases as a result of the total pressure in the bubble weakening, and therefore the bubble pressure have little effect on the cavitation; as the k value inside the gas bubble inside increases, the amplitude of the bubble increases gradually, in both expansion phase and the compression phase of sound wave, and so the cavitation is greater in sonochemical efficiency, and hence the single-atomic gases is used better than diatomic gases, but it should be noted that only the k value have no enough impact and the gas thermal conductivity also be taken into account on the effects of cavitation, if the thermal conductivity of gas is big, the heat accumulation inside the bubble during collapse will be more transmit to the surrounding liquid, so that the T_max values decreases, and cavitation reduces; with the temperature increasing, cavitation threshold decrease, cavitation has become easy to occur, but cavitation intensity becomes weaker; with the temperature lowering cavitation is more difficult to occur, but cavitation intensity becomes stronger, and so the temperature does not matter very much.Finally, this article summarizes the law of acoustic cavitation bubble radius changes under the different parameters of sound and how to optimize acoustic cavitation.