Numerical Analysis Of Single Bubble Dynamics In Ultrasonic Cavitation

Ultrasound has been extensively applied in many fields with the development of science and technology. Ultrasonic cavitation is the main mechanism that induce all kinds of physical, chemical and biological effects during these applications. Phenomenons such as high temperature and high pressure resulting from the collapse of the transient cavitation bubbles are responsible for all the observed effects of ultrasound. Acoustic cavitation is characterized by the dynamical evolution of clouds of bubbles. The investigation of single bubble dynamics is not only as a starting point towards a multi-bubble cavitation, but also as a basis for a more complete comprehension of the whole phenomenon of ultrasonic cavitation.Among the methods of researching single bubble dynamics, numerical analysis is a research method besides theoretical approaches and experimental means, and it is necessary at least for two reasons. First, an exact analytical treatment of the equations that model acoustic cavitation phenomenon is substantially impossible due to their high non-linearity;furthermore the cavitation bubble sizes in the range of microns, bubble dynamical period intervals in the range of microseconds or nanoseconds make experiments difficult to perform.Based on the Rayleigh-Plesset bubble dynamic equation under the consideration of liquid surface tension, viscosity and radiative resistance, this essay adopted numerical simulations to investigate single cavitation bubble dynamics with different kinds of acoustic driving. The following work has been done:(1) Analyzing the influence of acoustic frequency, acoustic pressure amplitude and initial bubble radius towards bubble dynamics respectively;With the increase of acoustic frequency, the bubble whose initial radius has been given will not collapse but vibrate continually, that is to say, cavitation is hard to occur. The collapse of bubble will become more violent with higher acoustic pressure, but overhigh pressure will delay the collapse or even make it never happen.(2) Analyzing bubble dynamics with harmonic excitation;Harmonic excitation will enhance the collapse of bubble, and there is best phase difference between the harmonics making the effects of cavitation more obvious.(3) Analyzing bubble dynamics with dual frequency acoustic drivings;More cavitation core will be formed under dual frequency drivings, so the effects of cavitation will be enhanced naturally.(4) Analyzing bubble dynamics with a sinusoidal wave driving with a pulse;Numerical simulations reveal that different inserted time, amplitude and width of pulse signal will influence maximum radius and collapse velocity of bubble.(5) Analyzing bubble dynamics with a rectangular wave driving or a triangular wave driving;Bubble will collapse more violently with a rectangular wave driving than it is driven by a triangular wave. This is because the rectangular wave occupies more power than the triangular wave during a same period of time.(6) Analyzing bubble dynamics with a sinusoidal amplitude modulation wave driving. The increase of modulation depth will weaken the effect of cavitation, and the frequency of modulation signal has a little influence on the bubble dynamics.Through the work which has been done above, the relationship between bubble dynamics and different kinds of acoustic driving was discussed;on the other hand, it provides theoretical support for choosing appropriate acoustic driving form to enhance cavitation effects in practical applications.