The Experimental Study And Theoretical Analysis Of Cavitation Bubble Movement And Coalescence In Ultrasound Field

The ship wake guided torpedoes have a good capacity of anti-interference and guiding accuracy, hit precision and well damage effect. However, there are lack of effective methods to defend the ship wake guided torpedoes at present, it is urgent to develop the technology to defense the ship wake guided torpedoes. There is a method use the ultrasonic energy make the bubble coalescence in the ship wake, and change the bubble size, distribution and density. Which can eliminate or reduce the ship wake characteristic detected by ship wake guided torpedoes, and defend to torpedoes as a result. The method based on the based on the theory of bubble movement and coalescence. This paper will use experimental method, theoretical analysis and numerical simulation methods to study bubble movement in acoustic field, different parameter to the effect of secondary Bjerkens force, and the mechanism of bubble coalescence in acoustic field. Main contents in the paper were as follows:1、The experimental study of bubble movement when the acoustic frequency is 22.4 kHz, and acoustic pressures are 10kPa-40kPa. When two bubbles far away, bubbles position change are very small, with decrease of the distance between two bubbles, two bubbles movement is quickly. It also find that when one bubble approached another bubble, a threshold distance was reached at which the secondary Bjerknes force became dominant. And when two bubbles small than the resonance size, the distance threshold is increase with the acoustic pressure increase. The experimental study of two bubbles movement when the acoustic frequency are 20kHz-100kHz. It find that two bubbles relative position is different in different frequencies, the bubbles position change large in high frequency compare to low frequency, And it is closely related to the distance of between two bubbles and bubbles radius. The experimental study when the acoustic pressures are 10kPa-120kPa and frequencies are 20kHz-100kHz dividedly. It is find that when the pressure is 30kPa, after two bubbles contact to each other, the film thickness between two bubbles and bubbles shape not changed obviously, but when the pressure is 120 kPa, it changed very big. At low frequency, the relative position change is not changed obviously after two bubbles contact, but it changed obviously at high frequency.2、Used the coupled equations of radial and translational motions do the simulation of bubble movement, there is a good agree with experiment result. And it is find that when the distance between two bubbles is far away, the buoyancy and primary Bjerknes force is the dominant force of two bubbles, when two bubbles move to close the secondary Bjerknes force is the dominant force between two bubbles. At the same time, the effect of the acoustic pressure on the secondary Bjerknes force has been studied, when two bubbles size smaller or bigger than the resonance size, the secondary force is attractive, and increases with the acoustic pressure increase. When two bubbles size between resonance size and more close to resonance size, the secondary force is repel at low pressure, and changed to attractive at high pressure. There is no obvious trend when the secondary force affected by the acoustic frequency, pressure, the equilibrium bubble radius and the distance between two bubbles. And analysis the reason of mentioned above the factors to the secondary between two bubbles, it is shown that the secondary force change was affected by two bubbles oscillation phase and amplitude.3、Used the theoretical method to analysis the factors of affect the bubble coalescence in different acoustic pressure 10 kPa to 120 kPa and 20 kHz to 100kHz. It is shown that bubble coalescence time is longer than the theoretical calculation time when absence of the acoustic field, and the the bubble coalescence time increase with the acoustic pressure increase in different acoustic pressure. And bubble bobble coalescence time is longer than the theoretical calculation time in different frequency, but there is no obvious trend. Bubble coalescence time affected by two bubble coalescence time, and proportional to the time the two bubble equivalent radius, which is similar when two bubbles coalescence in the absence of acoustic field. There are two important factors affect the bubbles coalescence tine in different acoustic pressure and frequency, the secondary force and the maximum oscillation velocity of two bubbles will affect two bubbles coalescence, and two bubbles coalescence time will increase with the secondary force between two bubbles and maximum oscillation velocity of two bubbles. The acoustic will affect two bubbles oscillation phase ant affect two bubbles coalescence finally. When two bubbles with the same phase, the liquid film between two bubbles will becomes thinner and when two bubbles out of phase the liquid film between two bubbles will becomes thicker, that will broken normal drainage process and affect bubble coalescence finally.