A Research Of Single Bubble Of Dynamics Properties For The Collapse Process

Cavitation is a common phenomenon in nature,especially in hydraulic machinery,which seriously affects the performance of the machine.Cavitation will bring serious problems such as noise,vibration and cavitation erosion to the equipment.The study of cavitation is heavily focused on the collapse process of single bubbles,and it is important to understand the movement of single bubbles for cavitation research.In practice,the contents of the bubble are gas/vapour,and according to the condensation properties of the bubble contents,the bubble contents are divided into two types:non-condensing gas and condensing gas（vapour）.The bubble dynamics properties of non-condensing gas are solved theoretically by the bubble dynamics equations,and the bubble evolutionary collapse process of condensing gas is solved by numerical simulation methods.In this paper,the numerical simulation results are compared with the experimental and theoretical values to verify the accuracy of the numerical simulation results.The evolutionary process of the bubble is obtained and the variation relationships between the bubble motion velocity,force,impact load and wall shear rate with time and non-dimensional wall distance（γ）are analysed.It is the main conclusions of this paper,a brief summary.1.For the problem of bubble dynamics of non-condensing gas,the oscillation characteristics of the bubble with and without external force driving conditions are solved numerically in this paper.It is shown that the bubble oscillates with gradually decaying amplitude without external drive,and the maximum collapse velocity of the bubble is 40m/s.The oscillation of the bubble with external drive is quite different,and when the driving pressure is 1.35times the atmospheric pressure,the bubble undergoes a rapid collapse process,and its collapse velocity exceeds the local speed of sound,and the contents of the bubble generate tens of thousands of atmospheric pressure and temperature,but the duration is short.2.Based on the equation of motion of the bubble in the near-wall region,the study of the bubble advection process shows that the centre of the bubble moves rapidly towards the wall at the end of the collapse and the resistance to the bubble is the greatest;the closer the initial bubble is to the wall the greater the speed of bubble advection and the greater the resistance.At the same time,the radiation sound pressure coefficient,which characterizes the radial vibration behaviour of the bubble,is proposed.It is found that the distance between the walls has a smaller effect on the radiation sound pressure coefficient,but has a more significant effect on the radiation sound pressure,and the closer the initial bubble is to the wall,the higher the radiation sound pressure at the wall.3.Numerical simulations were carried out for the case where the contents of the bubble were condensed gas,and the dynamics behaviour of the non-spherical bubble collapse process and during the collapse were investigated,as well as the effect of the bubble collapse process on the wall.The results show that the pressure wave radiated by the bubble oscillation is related to the bubble collapse velocity,the faster the collapse velocity,the stronger the flow field disturbance and the higher the radiated pressure.4.The influence factors of the wall damage were calculated and analysed,the results show that the impact load on the wall is the result of the interaction between the collapse pressure and the wall distance,the impact load on the wall is calculated to be 80 atmospheres maximum whenγ=3,whenγ=1,the wall shear rate is 8×10⁴s^-1 maximum,the shear rate decreases gradually with the increase ofγ.When the bubble is attached to the wall,the shear rate increases sharply asγdecreases.In this paper,the dynamic characteristics of the free field and near-wall area bubbles are studied,which can provide scientific and theoretical support for the prevention of cavitation damage.