| Cavitation bubble is one of the main causes of cavitation ersion in hydraulic machinery,when the cavitation generated bubbles collapse near the solid surface will produce microjets,high pressure,shock waves,exothermic processes,which lead to the change of the liquid velocity field and pressure distribution field,resulting in cavitation of the material surface.Because of the complex interaction between bubbles and walls,bubbles and liquid,and bubbles and bubbles during the motion of bubbles,which is very complex and difficult to study on a macroscopic scale.Therefore,this paper adopts the lattice Boltzmann method(LBM)coupled hydrothermodynamic model,taking into account the interaction between temperature and flow fields,to investigate the growth and collapse process of single cavitation bubbles in the near-wall region systematically,focusing on the effects of dimensionless bubble-wall spacing,initial input temperature,surface tension,wettability and wall temperature on the evolution process,collapse intensity and dynamic contact angle of cavitation bubbles.In addition,the interaction mechanism the strong and weak of equal and non-equal size double cavitation bubbles are systematically investigated,which additionally expand the complex interaction mechanisms of cavitation bubble populations.The main results are as follows.(1)The research model in this paper can simulate the evolution of bubbles attached to the wall and bubbles in the near-wall area,and obtain the dimensionless bubble-wall distance and the maximum radius as a function of each other.The relationship is power function at the dimensionless bubble-wall distance less than 1.6 and linear at the distance greater than 1.6.The initial critical radius increases with the increase of surface tension and the power function relationship between Weber number and maximum radius.And the smaller the surface tension is,the larger the cavitation bubble deformation is and the larger the microjet volume is produced.(2)The simulation results show that the initial input temperature affects the pressure evolution process inside the bubble nucleus,leading to different expansion rates of the bubble walls,but the final expansion rates are very close to each other.The higher the initial excitation temperature,the higher the collapse intensity,and the high temperature released during the first collapse may lead to oscillations in volume and radius.Too large an initial pressure can lead to the inability of the generated bubble nuclei to grow and eventually to condensation.(3)The complete growth and collapse processes during the cavitation bubble interaction were successfully simulated,and the strong and weak interaction mechanisms of equal and non-equal-sized double cavitation bubbles were systematically investigated.The critical distance to distinguish the strong and weak interaction mechanism between double equal-large cavitation bubbles is proposed.For the weak interaction process of non-equal-large double cavitation bubbles,the pressure wave generated by smaller cavitation bubbles leads to smaller deformation of larger cavitation bubbles in the final collapse stage and causes the generated non-equilibrium force to act on the liquid membrane,making it more difficult to rupture than equal-large double cavitation bubbles.(4)The thermofluid characteristics of the growth and collapse of wall cavitation bubbles under different wall wettability and temperature conditions were investigated,and the interaction between the temperature and flow fields was considered to understand the effect of wall temperature on the dynamic contact angle.It is concluded that the wall wettability has a great influence on the bubble morphology,and a higher growth rate is observed in the growth phase for non-wettable walls.However,due to the hysteresis effect,the contact point becomes a standing point at the contact point,resulting in a weakening of the collapse intensity on the non-wetting wall surface. |
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