| Cavitation is a physical phenomenon specifically occurs in fluids.The erosion caused by cavitation usually reduces the working efficiency and service life of hydraulic machinery.Hydrophobic surface has excellent resistance to corrosion due to the water repelling property,so it has potential application in solving the erosion caused by cavitation.In this dissertation,experiment and simulation methods are adopted to investigate the oscillation characteristics of the cavitation bubble near a hydrophobic wall surface.A single cavitation bubble is controllably produced by laser,therefore the oscillation characteristics of cavitation bubble near the horizontal and vertical walls with hydrophobic coating and related factors are explored.A simulation model of the cavitation bubble oscillating near hydrophobic surfaces is established.The oscillation characteristics of the cavitation bubble near the hydrophobic surface,the pressure field in the calculation domain and the distribution of jet velocity are analyzed.The main research contents and results are as follows:(1)The mechanism of laser-induced cavitation bubble was theoretically analyzed and the effect of liquid parameters on bubble oscillation characteristics was explored based on bubble dynamics.Meanwhile,the oscillating law of the cavitation bubble near the wall and its effects of micro-jet and shock wave were researched.These above provide a theoretical basis for the study on oscillation characteristics and mechanism of laser-induced cavitation bubble near a hydrophobic wall surface.(2)An experimental platform of laser-induced cavitation was established,and high-speed photography was used to obtain sequence graph of cavitation bubble near horizontal and vertical walls.The oscillation characteristics of cavitation bubble near the wall in different positions and the effect of hydrophobic coating were analyzed.The results show that the maximum diameter and oscillation period of cavitation bubble near the wall with hydrophobic coating is smaller than that near the ordinary wall without the hydrophobic coating for both the horizontal or vertical wall.The effect of the hydrophobic coating on bubble oscillation is more significant when the wall is placed horizontally.(3)The effects of laser energy,defocusing amount,type of hydrophobic coating and its thickness on the shape,maximum size and oscillation period of cavitation bubble were analyzed experimentally.The results show that the larger the contact angle of the hydrophobic coating,the smaller the maximum size and oscillation period of bubble near both the horizontal and vertical wall.Near the horizontal wall with hydrophobic coating,the maximum diameter of bubble increases with the increase of laser energy.The effect of coating thickness on bubble pulsation is relatively weak.Near the vertical wall with hydrophobic coating,the effect of hydrophobicity on the shape and oscillation characteristics of bubble is more significant under a smaller defocusing amount.The maximum size and oscillation period of bubble become smaller with the increase of the contact angle.The response of the hydrophobic wall to bubble can be observed.(4)ANSYS Fluent was utilized to simulate the oscillation behavior of laserinduced cavitation bubble near a hydrophobic wall surface.The pressure field and jet velocity distribution in the calculation domain were also analyzed.The simulation results show that the air film at the solid-liquid interface leads to a smaller bubble.The maximum size and oscillation period of the bubble decrease as the thickness of air film increases.The presence of air film can cause pressure diversion in the flow field.The velocity of the jet contacting the wall surface decreases with the increase of the thickness of air film,and the pressure of which acting on the wall is suppressed.The larger the relative distance between the bubble and wall surface,the smaller the influence of air film on bubble behavior,and the impact of jet on the wall surface is correspondingly enhanced. |
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