Research On The Interaction Between Cavitation Double Bubbles And The Instability Of Bubble Shape

When sound waves propagate in a liquid,the sound pressures fluctuate in time and space,and negative pressure appears which is lower than the static pressure state.When the liquid is in a state of negative pressure,small pressures or tensions have effect on the molecules of liquid.At the same time,the internal structural defects of the liquid(cavitation nuclei)will gradually grow to.form the visible cavity,which is the acoustic cavitation.Acoustic cavitation is an ancient and modern question,which has attracted much attention since it is discovered.Acoustic cavitation now is a hot issue in acoustics and physics.The collapse of cavitation bubbles is a near adiabatic process and results in the generation of high temperatures within these bubbles,and for this reason,these bubbles are also referred to as micro-reactors or hot-spots.The acoustic cavitation is also accompanied by the emission of light,referred to as sono-luminescence.In addition to the heat and light produced on bubble collapse,other mechanical and physical effects,such as shock wave formation,turbulent motion of the liquid,etc.are also generated during cavitation.The extreme physical conditions inside of the cavitation bubble and the strong sound effects result in a series of physical,chemical and biological effects,and show a broad application prospect.Although the applications of ultrasonic cavitation get a series of achievements,but in fact,due to the scale of the micro air bubble is micron level,and a little knowledge about the inside and surrounding of the air bubble in a violent vibration,the scale of ultrasonic cavitation is restricted.As a result,the basic theory researches of ultrasonic cavitation have great significance on the understanding and controlling of cavitation phenomenon.The ultrasonic cavitation is a group effect of a great number of bubbles,which is a multi-body problem.The interactions between bubbles are very complex.Therefore,it is very difficult to study the theoretical study of multi-bubble cavitation.Two bubbles are the basis of the model of multi-bubbles,so the theoretical study of double bubble cavitation is of great significance for multi-bubble cavitation.For this purpose,this article focuses on the interaction between two bubbles and the shape instability of two bubbles.We attempts to provide theoretical basis for the cavitation of multi-bubbles,and the main researches are as follows:(1)The mutual interaction of spherical bubbles and the impact factors were researched based on the double bubbles model in a strong acoustic field.The secondary Bjerknes force of two bubbles in a certain size range and the bubble structure were analyzed in a certain driving condition.The expression of the secondary Bjerknes force of a nonspherical bubble and a spherical bubble was obtained by considering the distortion of a gas bubble in an acoustic field.We numerical simulated the secondary Bjerknes force of two bubbles and discussed the influencing factors of the mutual interaction of a nonspherical and a spherical bubble.The results show that if the driving pressure is bigger than the Black threshold of the bubble but making the bubble oscillate stably,the difference of the secondary Bjerknes force of a nonspherical bubble and a spherical and two spherical bubbles is big in the first driving period.The secondary Bjerknesforce of a nonspherical bubble and a spherical bubble is several times and even morethan that of two spherical bubbles,and the force of a nonspherical bubble and aspherical bubble has a longer range.The secondary Bjerknes force of a nonsphericalbubbles and a spherical bubbles relates to these factors:the shape mode of the nonspherical,the relative position of two bubbles,distance between two bubbles,the initial radii of two bubbles,and driving pressure amplitude.(2)The energy of two bubbles with distortions was researched.We obtain he dynamic equations and shape instability equations of two nonspherical bubbles based on the Lagrangian equation.The influence of the mutual interaction of two nonspherical bubbles on the shape instability and the distortion amplitude of a gas bubble was researched.The results show that there are two kinds of coupled modes in the sound field:the shape coupled mode and the radial coupled mode.The coupled modes between two nonspherical bubbles depend on the shape mode of two bubbles.If the shape modes of two nonspherical bubbles are equal to each other,shape coupled mode and radial coupled mode coexist.If the shape modes of two nonspherical bubbles are not equal to each other,only radial coupled mode exist.The interaction of two bubbles caused by shape coupling and radial coupling can change the shape instabilities and the distortion amplitudes of bubbles.The influencing factors depend on the driving sound conditions,shape modes of two bubbles and initial radius of adjacent bubble.The influence of shape coupled between two bubbles on the instability of a gas bubble is bigger than that of radial coupled in the same driving condition.The synergy of shape coupled and radial coupled can decrease the areas of the instability of a gas bubble in a certain driving condition.The intensity of collapse of a gas bubble is reduced and the ability of resistance to nonspherical disturbances is increased in a certain driving condition.