Study Of Spoll Oscollation Induced Cavitation Based On Overset Mesh

Poppet valve has become a common and important control element in hydraulic system due to the advantages of good sealing,simple structure and strong anti-blocking ability,and is often used as a pressure regulating valve to adjust or limit the system pressure.During the working process,under the action of external excitation,the valve core is prone to axial oscillation,resulting in large fluctuations in the pressure of the entire hydraulic system.And the oscillation of the valve core will induce cavitation in the flow field,and the initial birth,development and collapse of cavitation will also cause pressure fluctuations.The oscillation phenomenon of the valve core is coupled with the cavitation phenomenon,which seriously affects the pressure regulation accuracy and working reliability of the hydraulic system.In view of the above problems,this paper takes the pilot stage pressure regulation poppet valve as the research object to study the cavitation phenomenon in the oscillation process of the spool,which is of great significance for the structural optimization of poppet valve and the whole hydraulic system.The main contents and innovations of this paper are as follows:(1)According to the characteristics of cavitation flow in the oscillation process of the valve core,starting from the two-phase flow model,the momentum equation,pressure equation and phase equation required for the two-phase cavitation solution are derived,combined with the cavitation model and the overset mesh algorithm,the above equations are compiled on the Open FOAM open source platform,and a two-phase cavitation flow solver with dynamic overset mesh function is developed for the second time.(2)The developed solver was used to numerically calculate the cavitation phenomenon of the valve core oscillation process,and the calculation results were compared with the results of the previous visualization experiment of the research group,which had a good degree of agreement,and verified the rationality of the secondary development solver and the accuracy of the numerical calculation results.(3)Combined with the experimental and numerical calculation results,the mechanism of cavitation in the valve closing stage and the valve opening stage of the valve oscillation is obtained.The oil in the valve cavity in the valve closing stage flows to the outlet by inertia,resulting in a wide range of low pressure area,which promotes the violent expansion of the gas core under the influence of low pressure,and produces secondary cavitation downstream of the valve cavity.The pressure gradient at the valve port in the valve opening stage is large,and the pressure difference drives the oil to generate a jet through the valve port at high speed,and the free shear layer on the side of the jet generates a local low pressure area,resulting in the formation of jet cavitation at the valve port;The jet movement forms a reverse jet and vortex in the valve cavity,and the pressure at the center of the vortex is lower than the saturated vapor pressure,resulting in a drifting cavitation deformed with the flow of oil.(4)On the basis of experimental data,the influence of different factors of the oscillation process of the valve core on the cavitation flow is studied.The results show that high inlet pressure and short spool oscillation period will promote cavitation during the spool oscillation process,while high outlet pressure and long spool oscillation cycle will inhibit cavitation generation during spool oscillation process.