Research On Transient Characteristics And Influencing Factors Of Laser-induced Cavitation Bubble

Cavitation is a kind of transient fluid phenomenon happening in the water conservancy machinery which leads to serious damage of the key parts of the equipment,and then the working efficiency and the service life will be decreased.Laser-induced cavitation is an important way to study the mechanism of cavitation.The experimental results show that the cavitation can be applied to the field of material surface strengthening and micromachining by controlling some parameters.In this paper,a combination of numerical simulation and experimental research is employed to study the transient characteristics of the cavitation bubble in different environments such as the infinite domain,near the solid wall and the "V" structure.And the influence of temperature,laser energy and the defocusing amount on the transient characteristics of the cavitation bubble induced by laser is researched.The mainly results are as follows: Firstly,the transient characteristics and the velocity distribution of cavitation in different environment were analyzed.The boundary conditions were set in Fluent to simulate the oscillation of the laser-induced cavitation bubble in infinite field and near the solid wall to study the velocity field distribution in the cavitation bubble.The simulation results show that the cavitation bubble has the tendency to move to the solid wall during pulsation.A velocity field similar to the micro-jet forms in the internal of the cavitation bubble at the same time which indicates that the cavitation bubble has the necessary condition for the forming of the micro-jet.Meanwhile,the variation of velocity field means that the cavitation bubble rotation exists during pulsation.Secondly,the sequence diagrams captured by the high-speed camera are processed to get the sequence diagrams of the single bubble boundary,bubble wall,pulsation velocity and the bubble diameter.Thirdly,comparing and analyzing the conditions of bubble generation and pulsation in the infinite domain,near the solid wall and the in the "V" structure.It is found that the laser energy required to produce cavitation bubble in the infinite domain is higher,while the formation of the cavitation bubble in the "V" structure requires a certain amount of defocusing amount.Meanwhile,the study shows that the bubble pulsation cycle and size of the cavitation bubble in the "V" structure are smaller than those in the other two environments.Fourthly,the influence of the temperature on cavitation bubble in different environment is found in this paper.The influence of temperature on the maximum pulsation diameter,cycle and velocity of the cavitation bubble near the solid wall is investigated through experiments.The research shows that temperature is an important factor on the bubble pulsation cycle and the maximum diameter,but it has little effect on the velocity of the bubble.The maximum diameter of the cavitation bubble increases with an increasing in the temperature.When the temperature is about 330 K,the effect of temperature on the maximum diameter of the cavitation bubble is relatively low.The optimization formulation of the cycle on the basis of the experimental results and the periodic equation proposed by Rayleigh is proposed due to the obvious effect of temperature on cavitation bubble pulsation,and the trend is similar to the relationship between the temperature and the vapor pressure.