Experimental Investigations Of The Mechanisms Of The Interaction Between A Cavitation Bubble And Spherical Particles

Cavitation exists widely in nature.When there are asymmetric boundary conditions around cavitation bubbles,they will collapse asymmetrically,then forming various liquid jets and emitting shock waves.In past decades,the dynamics of a cavitation bubble near a solid boundary,an elastic boundary or a free surface have been researched intensively.However,there are lack of in-depth study of bubble-particle interactions near various boundaries,which are the essential issues for solving the problems of erosion through synergetic effects between cavitation erosion and particle abrasion in silt-laden flow in hydraulic machinery.In this thesis,with the aid of the high-speed camera,the interactions between a laser-generated cavitation bubble and a spherical particle are investigated experimentally in an infinite field or near a solid boundary.The bubble dynamics and particle movement are analyzed qualitatively and quantitatively.Experimental platform is built to generate a laser cavitation bubble.The experimental platform is composed of laser device,focusing lens group,light source and high-speed camera.The cavitation bubble generated by the experimental platform has a smooth and spherical surface.Firstly,the interactions between a laser-generated cavitation bubble and a fixed particle or a suspended particle are investigated experimentally in the infinite space based on the experimental platform.The non-dimensional distance ?(the closest distance between the center of the trigger position of a cavitation bubble and a fixed particle/ the maximum radius of the bubble during its oscillations)and the particle diameter ratio ?(a fixed particle radius/ the maximum radius of the bubble during its oscillations)have influences on bubble dynamics near a fixed particle.When ? =1.5,the corresponding range of ? for the forming a counterjet during bubble rebound stage is 1.1-1.5.The nondimensional distance ?(the closest distance between the center of the trigger position of a cavitation bubble and the initial position of a suspended particle/ the maximum radius of the bubble during its oscillations)and the particle diameter ratio ?(a suspended particle radius/the maximum radius of the bubble during its oscillations)have influences on bubble dynamics and particle movement.With the increase of ? at a constant value of ?,the cavitation bubble evolution has repulsive effect,no obvious effect and attractive effect on a suspended particle,and no obvious effect corresponding to ? is near 1.When ? =0.72,1 and 1.3,the corresponding range of ? for bubble separation during rebound stage are 0.07-0.73,0.03-0.39 and 0.02-0.23,respectively.Secondly,the interactions between a laser-generated cavitation bubble and a suspended particle near a solid boundary are investigated experimentally.When ? equals to 1,the non-dimensional distance ? and ?(the perpendicular distance between the centre of a suspended particle and a solid boundary/ the maximum radius of the bubble during its oscillations)have influences on bubble dynamics and particle movement.The existence of a solid boundary makes the bubble evolution as a whole,which weakens the tendency of the bubble separation.The cavitation bubble evolution on a suspended particle movement has a more wide scope of ? and stronger effects.The particle has a greater tendency movement towards the bubble.When a solid boundary is very close to the bubble(? =1 and 1.05),the cavitation bubble evolution has only attractive effect on a suspended particle in the horizontal direction.When a solid boundary is far from the bubble(? =1.93,2.83,3.85,4.63 and ?),the cavitation bubble evolution has repulsive effect,no obvious effect and attractive effect on a suspended particle with the increase of ?,and no obvious effect corresponding to ? are 0.15,0.3,0.65,0.8 and 0.98,respectively.Thirdly,the interactions between a laser-generated cavitation bubble and a suspended particle near a fixed particle are investigated experimentally.When ? =1 and ? =1,respectively,the non-dimensional distance ? and ? have influences on bubble dynamics and particle movement.The effects of a fixed particle on the interactions between a cavitation bubble and a suspended particle are similar to the effects of a solid boundary.However,compared with the influences of a solid boundary,the inhibition effects of a fixed particle on bubble separation near a suspended particle are weaker in intensity and smaller in range.When ?(1.05 and 2)is equivalent to ?(1 and 1.93),the ? range of repulsive effect on a suspended particle is larger under the influences of a fixed particle.Finally,in order to eliminate the additional effects of fixing a moving particle,the interactions between a cavitation bubble and a free-settling particle are investigated experimentally.The turning point of the jet away from the particle during the first collapse of a cavitation bubble near a free-settling particle corresponding to ? is 0.5.The turning point of the jet away from the particle during the second collapse of a cavitation bubble near a free-settling particle corresponding to ? is 0.8.The cavitation bubble evolution has repulsive effect,no obvious effect and attractive effect on a free-settling particle with the increase of ?,and no obvious effect corresponding to ? is 0.8.In addition,the influences a cavitation bubble on the movement of a free-settling particle near a solid boundary are analyzed.The liquid jet is observed to drive a particle towards a solid boundary.When ? and ?(the angle between the line of the center of the trigger position of a cavitation bubble and the center of a particle and the horizontal line)change,the driving forces of a free-settling particle movement correspond to different evolution stages of a cavitation bubble.