Research On The Flow Visualization And Cavitation Of Poppet Valve Flow Field Based On Dynamic Mesh Technique

The poppet valve has the advantages of good sealing performance, large flow area, energy-saving feature, easy operation, and it is insensitive to hydraulic medium, which has been applied widely in hydraulic system, especially in cartridge valve. The control of poppet valve to the hydraulic system is realized by adjusting the flow regime of internal liquid. So in order to improve the poppet valve performance, the flow regime of valve internal liquid should be further studied, and the relationship between flow passage shape, flow field flow regime and failure mechanism should be researched from the flow field aspect.There still exists some deficiencies and insufficiency in the present study about poppet valve: 1) It can be found that the current calculation method about flow area of poppet valve still has problems according to the experiment data.The traditional formula about the poppet valve flow area is derived based on the poppet valve which owns complete conical surface, and the formula is appropriate when the spool of poppet valve owning incomplete conical surface moves in small range. However, the traditional formula is inapplicable for larger displacement. 2) The previous numerical analyses about flow field are limited tothe steady method or directly give a speed to the spool, which makes it difficult to actually simulate the movement of the spool and varieties of flow field. And in real conditions, opening and closing of the spool have a great influence on cavitation phenomenon, the present studies are unable to actually reflect the generation and development of cavitation.According to the existing problems, the main research contents are determined as follows:Firstly, the flow field of poppet valve owning complete conical surface and poppet valve owning incomplete conical surface was meshed by using pre-post software—Icem. The flow field of the two kinds poppet valves were simulated by the software—Fluent, which is computational fluid dynamic software. What’s more, the different flow regime of interior flow field of two kinds of poppet valve under the same condition were analyzed and studied. And the different discharge characteristics between two poppet valves were compared from the perspective of flow field. Research results show that when the displacement of spool is small and working condition is diverged, the flow field characteristics of this two kinds poppet valves are almost same, and cross sections of passages which play the role of throttling are at the same location. The displacement of spool is large and working condition is diverged, because poppet valve owning incomplete conical surface doesn’t has the diversion function, and the cone-frustums lateral surface conformed by the vertex of right-angular side of valve seat and the vertex of conical surface of valve spool has the function ofsubstantially contracting the fluid, the position of cross section of passage changed. Then through the combination of the flow field analysis and the theoretical derivation, the position and scale of flow area when the displacement of valve core is large and it is deducted.Secondly, the transient flow field of the cartridge valve in the opening process is simulated by combing computational fluid dynamics software FLUENT with 6DOF model of dynamic mesh technique. The movement of the spool is decided by flow force which exerts on it. The spool stops moving when forces are balanced. Compared with the previous research methods, the new method not only can obtain consistent results with the actual spool motion, but also can avoid writing more complex UDF functions. By comparing numerical simulation results about the spool displacement, pressure of the control chamber and the steady flow of inlet and outlet with the experiment results, it is verified that the proposed method can really simulate the transient flow field of the cartridge valve in the opening process. On this basis, the transient flow field with cavitation phenomenon of the cartridge valve is simulated and the generation and development process of cavitation is observed. And by comparing the transient simulation and steady-state simulation of cavitation field, the results show that the two have obvious differences. For the flow field with cavitation, if the transient simulation is replaced by steady-state simulation, it will cause some errors.