Research On Dynamics Of Acoustic Cavitation Bubble

Acoustic cavitation refers to the phenomenon that the original tiny bubbles in the liquid grow into visible,micron level bubbles.(The the original tiny bubbles is also called cavitation core or the defect in the liquid.)The bubbles formed are called acoustic cavitation bubbles,referred to as cavitation bubbles.Under the action of ultrasonic wave,the radial motion of cavitation bubble shows nonlinear characteristics of slow expansion,then sharp collapse,and finally rebound.In the process of rapid collapse of cavitation bubble,extreme high temperature and high pressure will be generated in its interior,which will lead to the emission of light by excited atoms,molecules or ions inside the cavitation bubble,namely sonoluminescence.This thesis mainly introduces the theoretical and preliminary experimental study of cavitation bubble dynamics.Theoretical modeling and numerical analysis are carried out for single and two cavitation bubbles.The dynamics of single and double cavitation bubbles in spherical acoustic resonators were observed by ultrasonic levitation technique,and some experimental parameters were obtained.Firstly,the dynamic model of single bubble driven by ultrasonic is presented.The coupling model of pulsation,translation and deformation of single cavitation bubble is established by using fluid mechanics theory and perturbation theory,and the equations described radial vibration,translation and deformation of single cavitation bubble in ultrasound field are derived.The evolutions of bubble radius,center displacement and surface deformation with time are obtained by numerical calculation of these three equations.The results show that:(1)when the initial radius of the bubble and the driving sound pressure are constant,the center initial translation velocity of the bubble increases,the radial vibration of the bubble is almost constant,the displacement and deformation of the bubble increase,and the non-spherical vibration of the bubble becomes more obvious.(2)When the initial translation velocity is small,the unstable region of the bubble phase diagram is concentrated in the region of high driven sound pressure;With the increase of the center initial translation velocity of the bubble,both the bubble radius and the driving sound pressure are stable in a small region,and the unstable space range increases with the increase of the initial translation velocity.(3)Bubbles have different vibration amplitudes at different positions in the acoustic standing wave field.The closer the bubble is to the antinode,the larger its radial vibration amplitude is,but the smaller its translation and shape variable change are.Secondly,the dynamic model of two bubbles under ultrasound is presented.Based on potential flow theory and perturbation theory,the coupling model of pulsation,translation and deformation of two cavitation bubbles is established,and the radial vibration,translation and deformation equations of two cavitation bubbles in ultrasonic field are derived.The influences of initial translational velocity on the radial pulsation,translational deformation,vibration and stability of two bubbles are studied,respectively.The results show that the radial radius,central translational displacement and surface deformation of the two bubbles show periodicity.With the increase of initial translation velocity,the two bubbles vibration period decreases.When the initial translation velocity reaches 3m/s,the two bubbles are in the completely unstable region in the R₀₁-R₀₂ phase diagram.Thirdly,the experimental study of single and double cavitation bubbles.Based on ultrasonic levitation technology,the dynamic behaviors of single and double cavitation bubbles were observed in a spherical acoustic resonator by controlling ultrasonic frequency,sound pressure amplitude and liquid gas content,and the corresponding parameter space was obtained.