Study On Acoustic Propagation In Bubble Liquid

The multi bubble ultrasonic cavitation is a very important theoretical problem of cavitation, especially which happened in bubbly liquids, and the application of the bubble’s cavitation phenomenon is mainly in the bubbly liquids. Therefore, the study of ultrasonic cavitation in the bubbly liquids shows the vitally importance both in theory and in practice. Aiming at this question, we have done some research on the acoustic wave propagation in the bubbly liquids. The main content are as follows:In the first part, this paper summarizes the research and the current situation of bubble cavitation and acoustic wave propagation in a bubbly liquids.In the second part, some research on the basic problems of bubble dynamics and fluid dynamics have been done. In the bubble dynamic part, we give a study on the oscillation of bubble in liquids, including the static equilibrium problems of bubble in the pure liquid, acoustic scattering problem of the bubble in the linear sound field and the bubble’s nonlinear vibration problems. We develop a theoretical model of acoustic scattering of bubbles, giving a study on the process of acoustic scattering of bubble and the influence of surface tension on the scattering. We found that the influence of surface tension on bubble scattering for both single bubble and multiple bubbles, is relatively obvious when the bubbles are small and the driving frequency is low. Results show that for the low acoustic frequency and small radius gas bubbles, surface tension’s effect on the acoustic scattering still can not be ignored. In addition, the vibration process of single bubble has been studied under the condition when the liquid contains a lot of bubbles. The oscillation model of bubble is established in the case which in consideration of other bubble’s scattering, we give a study on the vibration process of a single bubble in the bubbly liquids. We found that in the consideration of the bubble’s scattering, the volume or size of a single bubble shows some different scenarios, which as follows:the bubble’s vibration does not occur cavitation phenomenon; the cavitation occurs periodically; after a cavitation phenomenon, the bubble size remained at a value near the oscillation size; the bubble growth and maintained at near the maximum. The vibration of bubble should be considering the situation of bubble size, volume fraction and the driving sound field.In the third part, we focus on the acoustic wave propagation in bubbly liquids, including linear wave propagation and nonlinear wave propagation. For the linear wave propagation, we set up two kinds of bubbly liquids model, which are the diffusion model and the effective medium model, and we give a study on the waves linear propagation in the bubbly liquids using the effective medium model of bubbly liquids particularly. we found that, due to the scattering and the vibration of bubbles lie in the acoustic field, the energy of acoustic wave shows bigger attenuation in the process of wave propagation. On the other hand, the bubbles in the liquid change the acoustic wave parameters of liquid, so the wave speed is also changed significantly, and the changes shows that the increasing of volume fraction of bubble will increase the attenuation of bubbly liquids and will reduce the velocity of wave propagation. For the finite amplitude sound wave propagate in the bubbly liquids and the nonlinear vibration of bubble will occur, we set up a nonlinear model of bubble oscillation. In the nonlinear model, considering the interaction between bubbles and the sound field, we focuses on the research of the energy attenuation of acoustic wave in the case. We found that, due to the nonlinear oscillation of the bubble, the reduction of the acoustic energy performance in the following aspects:part of sound energy transform into the kinetic energy and potential energy of the fluid around the bubble by the oscillation of the bubble; during the process of bubble oscillation, part of acoustic energy was transferred from the bubble to the liquid by heat conduction; the dissipation of acoustic energy was caused for the bubble to overcome the liquid viscous; some sound energy was radiated in the form of harmonic waves when the bubble oscillate as the secondary sound source. The wave nonlinear propagation is simulated in the bubbly liquids, and found driving time, the number and the size of the bubble will all have an impact on the distribution of the sound field in the bubbly liquids, the sound energy is difficult to propagate forward in this field, and will be limited in the vicinity of the source of sound.Finally, the theoretical results were compared with the experimental data, and it was found in certain degree that they are in good agreement.