Laser-induced Bubble Dynamics In Several Specific Mechanical Environments

Cvitation bubble has application value in many fields such as underwater explosions,gas gun bubbles,hydraulics,drag reduction,ultrasonic cleaning,ultrasonic imaging,lithotripsy,precision machining microfluidics,et.al.The interaction between bubbles and the surrounding environment is the core of the former engineering fields.This article mainly focuses on the research of bubble dynamics that can be artificially controlled.Numerical simulations and experiments are the main tools.The oscillation characteristics of bubbles in different environments and their interactions with the environment are mainly studied.A three-dimensional bubble multiphase flow model is established to study the dynamics of bubbles at different distances from interfaces.By considering the viscosity,surface tension and compressibility of materials on both sides of the interface,this model simulates the dynamics process of bubbles near free interface,water-oil interface and liquid-solid interface in adiabatic process.The results show that the oscillations of bubbles presents different styles under different distance conditions.In particular,when the distance between bubbles and interfaces is within 0.3 times of bubble radius,oil boundary and solid boundary generate viscous layer in flow field,which leads to transverse contraction impact when bubbles collapse,thus forming special jets;while free interface will burst towards free gas domain.In view of the unclear movement mechanism of bubbles simultaneously affected by multiple bubbles from different directions,a laser-induced three-bubble array and transient detection system were built.The dynamics of inner and outer bubbles in three linearly arranged bubble arrays with the same phase and size was analyzed using the three-dimensional bubble multiphase flow model and the system.The results show that the outer bubbles in the array behave similarly to the bubbles near the solid wall,but the central bubble in the array exhibits stretching,breaking,compression and other phenomena due to interaction between two bubbles in different directions.The collapse jet of the outer bubble produces a circular jet orthogonal to the arrangement direction inside the center bubble through collision under certain conditions,which may cut off the middle bubble.In order to artificially control the enhancement or weakeness of bubble collapse,a pressure wave generating device for dynamic interaction between bubble and pressure wave was developed.Based on Keller-Miksis model theory,we analyzed the dynamics process.Results show that maximum bubble radius and collapse speed can be changed by controlling relative time difference and length between pressure wave and bubble.A special phenomenon that radiation sound pressure enhancement will be formed when a certain large radius bubble is forced to collapse was also found in experiment.Then theoretical study was carried out on interaction between sine pressure wave with amplitude0-100 bar and period 0.5-5 times first oscillation period of bubble.Results show that relative low frequency or high amplitude sine pressure wave will cause maximum radius expansion beyond limit for bubble which can reach 10 times bubble original maximum radius;radiation sound pressure enhancement or weakness which can reach maximum 1000 times or minimum 0.01 times depends on phase position during oscillation and collapse stage.The research results of this article have reference value for clarifying the interaction mechanism between bubbles and the environment;provide theoretical and experimental basis for in-depth understanding of the dynamics of water phase change in complex flow field environment;and have application value for enhancing and weakening artificially controlled cavitation phenomena.