Experimental Study On Cavitation Characteristics Near Curved Wall Surface

Cavitation phenomenon exists widely in nature and is closely related to engineering practice.When there is a boundary around the cavitation bubble,the spherical symmetry of the cavitation bubble will be destroyed due to the change of flow field.Thus there are generating jet flow and shock wave in the collapse process,which will affect the safe and stable operation of hydraulic machinery.At present,many experts and scholars have carried out a lot of research on the dynamics of cavitation bubbles under different boundary conditions,but the research on the dynamics of cavitation bubbles under curved surface boundary conditions remains to be further in-depth.The surface of hydraulic machinery is usually not a straight wall but a rigid wall with a certain curvature.So the basic research on cavitation characteristics under curved surface boundary is the key to solve the problem of reducing cavitation during the operation of hydraulic machinery.In this paper,based on the principle of laser induced cavitation,an experimental platform was built.The experimental platform uses high-speed photography technology,and the dynamics characteristics of a single cavitation bubble under different surface boundaries and different distances are analyzed.During the study,the laser cavitation experiment platform is built,which includes three parts:cavitation bubble generation system,data acquisition system and signal transmission system.Based on the experimental platform,the cavitation phenomenon of the cavitation bubble near the boundary of the curved wall is investigated.The shape of cavitation bubble is mainly affected by distance and surface radius when the surface boundary evolves.With the change of dimensionless distance,the shape of cavitation bubble in the first period presents a neck-droplet-elliptic-nearly spherical rule in turn,while with the change of dimensionless surface radius,it presents a spheroidal-ellipticdroplet rule in turn.Secondly,the changes of cavitation bubble radius,collapse time and centroid distance near surface boundary are quantitatively analyzed.The results show that the closer the surface boundary is to the cavitation bubble,the stronger the obstruction effect on the cavitation bubble is,resulting in the decrease of the maximum radius of the cavitation bubble,the extension of the collapse time and the larger the centroid movement distance.With the increase of the radius of the dimensionless surface,the maximum radius of the cavitation becomes larger,the effect of cavitation bubble collapse time delay is weakened and the movement distance of the centroid decreases.Finally,it is found that the surface boundary has both wall effect and surface effect on the cavitation bubble,and both of them work together to influence the cavitation phenomenon near surface boundary.