| Hydraulic transmission is widely used in machine tool forging,metallurgy,military machinery,agricultural machinery,aerospace navigation and many other fields because it can achieve large thrust and torque,and has the advantages of high transmission power,small size,easy to realize automatic control,stable and safe operation.Axial piston pump,as a dynamic component of hydraulic transmission,drives swashplate by rotating spindle to drive plunger to do reciprocating motion,so as to realize the process of oil suction and discharge and the conversion of mechanical energy and hydraulic energy.Due to the complex internal structure of piston pump,when it works normally,the flow field pressure and fluid flow state are irregular,which will inevitably produce cavitation effect.Cavitation will directly damage the pump,reduce the volume efficiency of the pump,and cause vibration,noise and other hydraulic faults,further reducing the service life of the piston pump.The cavitation process includes three stages: bubble formation,bubble growth and bubble rupture.The collapse of cavitation bubble will release huge energy instantaneously,resulting in the damage of pump wall,and the local thermal effect will be produced by the bubble burst and the friction in the fluid during the jet process,which will increase the temperature.As the constitutive property of hydraulic oil,viscosity will decrease with the increase of temperature,which will eventually lead to the aggravation of cavitation effect and the increase of oil film leakage.With the increase of working time,the viscosity temperature effect of hydraulic oil will have a greater impact on the pump.The purpose of this study is to provide theoretical support for the optimization of the piston pump through cavitation research,improve the service life of the piston pump,and reduce the flow pulsation and pressure pulsation of the piston pump.Compared with the previous study on the flow field in the pump,this study first considered the time-varying of oil viscosity with temperature,and comprehensively considered the influence of the complete friction pair oil film leakage on the pump performance and cavitation.Through the CFD visualization analysis,the beginning,peak value and dissipation process of cavitation jet under the change of viscosity temperature were discussed.Through the simulation results,the influence of damping groove on cavitating jet is analyzed,and the structure optimization scheme of damping groove of valve plate is explored.Firstly,by analyzing the working principle of swash plate axial piston pump and the distribution process of spherical distribution,the influence of plane distribution on sealing and stability is highlighted.Through the analysis of the difference between the inclined waist hole and the straight waist hole,the advantages of the inclined waist hole in the flow distribution process and reducing cavitation are explained.Then the relationship between dynamic viscosity and temperature change of hydraulic oil is introduced,and the viscosity temperature coefficient is finally determined,which provides a theoretical basis for the subsequent simulation analysis under the condition of viscosity temperature.Secondly,the 3D simplified model of axial piston pump is established in Solid Works,and the fluid domain in the pump is extracted.The fluid domain of each part is assembled,and the coordinate origin and the coordinate axis of each direction are defined.Then,it is imported into pumplinx.In the meshing process,the advanced sliding grid and dynamic grid technology are used to define the rotor part.In order to reduce the error,three pairs of micron level key friction pair oil films are created in pumplinx and defined by UDF.The dynamic viscosity of oil is set by function compilation,and the changes of temperature,viscosity,jet velocity and air content are analyzed and compared in the process of cavitation jet under the conditions of real-time viscosity temperature change and constant viscosity.The results are verified by durability test,and it is concluded that the viscosity temperature characteristics will aggravate the cavitation effect.Finally,because the cavitation effect is inevitable in the piston pump,in order to suppress the cavitation effect,this study proposes a structural optimization scheme of the valve plate damping groove composed of three damping holes.Under the same boundary conditions,the changes of gas content and pressure field were analyzed by CFD visualization.The results show that the cavitation effect is obviously suppressed and the pressure fluctuation is reduced,which is beneficial to reduce the noise and flow fluctuation. |
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