Research On Unsteady Cavitation Characteristics Of Flow Field In Hydraulic Throttle Valve

As a very important basic component in hydraulic transmission and control,hydraulic throttle valve has the characteristics of good sealing and anti-pollution ability and is widely used in hydraulic systems.However,when cavitation occurs in the throttle valve,the periodic collapse of cavitation causes the pressure in the valve to oscillate,affecting the stability of the system,and the pressure shock caused by the collapse of the vacuole on the surface of the valve core causes the surface metal of the valve core to flake off.Cavitation has seriously affected the service life of the throttle valve.Therefore,it is of great significance to study the cavitation phenomenon inside the throttle valve.In this paper,a combination of theoretical analysis,numerical simulation and experimental research is used to study the unsteady cavitation characteristics of the flow field in the throttle valve under different structural parameters and different operating parameters,including: evolution of cavitation structure.The influence of process and cycle characteristics,different cavitation stages on the velocity field,and the effect of cavitation collapse on the pressure pulsation in the downstream flow channels in the valve.The combination of numerical simulation and experimental research methods were used,studying the unsteady cavitation characteristics of the flow field in a hydraulic throttle valve under a fixed operating condition were studied.The results of the study indicate that: the development of cavitation is an unsteady process.Its development and change can be mainly divided into three processes: cavitation,shedding and collapse.Compared with the initial stage of cavitation,there is a wider high-velocity distribution zone in the collapse stage of cavitation,and the degree of velocity fluctuation is relatively more severe.At the same time,there are opposite jet regions at different positions near the wall surface,and different section position corresponding to the different intensity of the reverse jet.The pressure pulsations at different monitoring points have the same dominant frequency,which is basically the same as the evolution cycle of the cavitation structure.Aiming at the influence of the change of operating parameters on the unsteady cavitation characteristics of the throttle valve,the influence of the ratio of the length and diameter ratio of the valve core and the ratio of the upstream and downstream channel diameter to the cavitation field,velocity field and pressure field in the valve is studied by the combination of numerical simulation and theoretical analysis.The results shows that: in different spool length diameter ratio,periodic of cavitation development and the length of free cavity changed greatly,and the cavitation period first increases and then decreases with the increase of the aspect ratio of the spool.but with respect to the effect of the head radius R0 on the cavitation flow field,changing the length of the head section of the valve plug has a greater influence on the cavitation flow field.In addition,the cavitation cycle also shows a tendency of increasing first and then decreasing with the increase of the upstream and downstream flow passage diameter ratio.While keeping the upstream runner radius constant and reducing the downstream runner radius,the cavitation area of the valve plug head and the amplitude of the pressure pulsation gradually increase,but the radius of the upper flow passage of the throttle valve is changed to the flow field in the valve.Less affected.Aiming at the influence of structural parameters change on the unsteady cavitation characteristics in the throttle valve,the combination of numerical simulation and experimental research methods were used to study the change of inlet and outlet pressure difference and opening to the cavitation field and velocity field in the valve.The impact of the pressure field,the research results show that: with the increase of pressure difference between inlet and outlet,the maximum length of free cavitation and cavitation cycle are also relatively increased.At the same time,with the increase of the pressure difference between the inlet and outlet,the time of the trough period of the pressure pulsation will move forward.When the differential pressure at the inlet and outlet remains unchanged and the opening of the valve is increased,the speed of the medium in the valve chamber increases in the axial direction,and the speed of the freetype cavitation increases as the mainstream moves downstream,and the cavitation period becomes smaller.The time from production to collapse of free cavitation will decrease.When the throttle opening is increased,the cavitation area of the spool head will gradually decrease.