| Hydraulic technology is one of the key technologies for realizing modern transmission and control.With the development of science and technology,the performance requirements for valve components in hydraulic systems are also increasing.As an important basic element in hydraulic transmission and control,the hydraulic poppet valve has the characteristics of good sealing performance,strong over-current capability,fast response,strong antipollution ability and simple structure.However the flow state of the fluid is very complicated when the poppet valve is in operation.The liquid easily vortexes when passing through the valve port.Then cavitation phenomenon will inevitably occur and the performance of the valve will be affected.At the same time,the hydraulic power is also the main factor affecting the valve performance.Therefore,it is of great significance to study the cavitation phenomenon and hydraulic power of the hydraulic valve to improve the performance of the valve.The thesis is aimed at the common poppet valve and complex flow channel poppet valve of the with pure water as the specific research object.The unidirectional flow model can not accurately simulate the flow field because it neglects the change of some parameters of the fluid caused by the cavitation phenomenon when the flow flied is simulated by Fluent.Therefore,the combination of three-dimensional two-phase numerical simulation and experimental verification was studied,including different valve core geometries and different valve core openings,in order to seek the effect of the position and number of bubbles generated.According to the characteristics of the hydraulic poppet valve,threedimensional flow field models of different valve core opening valves were established to divide the mesh.Two-phase flow model,cavitation model and standard k-? turbulence model were used to obtain the pressure field velocity of the flow field ? cloud distributions of field and gas volume fractions.The influence characteristics of the boundary conditions and the dimensions of the key geometry on the poppet-valve cavitation were analyzed.It was found that cavitation occurred in the lowest pressure region of the flow field.It is found that the boundary conditions have a significant effect on the valving of the poppet valve.The inlet pressure is reduced,the low pressure area is reduced,the pressure drop is reduced,and the cavitation are weakened.Otherwise,the cavitation are weakened.The wider the valve opening the larger,the opening of the valve core.The larger the area,the lower the flow velocity and the pressure drop,so that the cavitation is weakened or even completely suppressed.The spool angle has a significant effect on the cavitation,which will reduce the cavitation when the poppet angle decreases.For the flat bottom poppet valves are more prone to produce cavitation.Under the same conditions,internal-flow poppet valves are easier to produce cavitation than out-flow poppet valves.The test bench for cavitation and hydraulic power is designed to use plexiglass materials with good transparency to manufacture valve blocks.High-speed cameras are used to capture the generation,development,and collapse of bubbles and cavities in valves.Starting from the inflow and outflow conditions,the area of cavitation and the degree of occurrence under different conditions were obtained,which verified the feasibility and accuracy of thesimulation.It is also concluded that as the opening of the spool increases,the area where cavitation occurs moves toward the outlet.Due to the existence of the hydraulic power,the input signal of the poppet valve may have an unpredictable relationship with the displacement of the valve core,and the instability of the hydraulic valve may affect the stability and reliability of the entire system.By calculating the poppet pressure of the poppet valve core,the steady-state hydraulic force of the valve core can be obtained.During the test,force sensors are used to collect force on the valve core. |
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