Instantaneous Cavitation Phenomenon In V Shape Valve When The Flow Is Cut Off

Hydraulic valve is the centre of the fluid in the hydraulic system control,with the development of hydraulic technology to a higher power density,there will be a larger pressure gradient in the hydraulic valve when the flow in the hydraulic line is cut off.The study found that severe cavitation phenomenon appear in the hydraulic valve when the flow is cut off.The pressure wave caused by cavity collapse will cause serious negative impact on the performance of the hydraulic valve and far from its rated conditions.Therefore,it is very important to study the transient characteristics of hydraulic valve when its flow is cut off for some occasions which require high reliability.However,there are few studies on the transient cavitation phenomenon in the hydraulic valve when the flow is cut off.Therefore,we used the visualization method to carry out an experimental study on the cavitation phenomenon inside the valve when the hydraulic pipeline flow is cut off.The research contents of this paper are as follows:The first chapter summarizes the research significance of this topic,the research status of cavitation in hydraulic valves,high-speed camera technology,the mechanism of cavitation in the oil and the main research direction and content of this paper.The second chapter of simplified two-dimensional flow model was structured grid.then adopt the Schnerr-Sauer cavitation model,Zwart-Gerber-Belamri cavitation model and Singhal cavitation model based on the phase transition to simulated the cavitation flow.Comparing the calculated results and experimental results,we've found the difference of these three model when simulating the oil cavitation.It is found that the results of Singhal model with modified turbulent viscosity are better than those of the previous two models.Then through the results of simulating oil cavitation,the limitation of cavitation model based on phase transformation is discussed.We found that the cavitation model based on phase change cannot simulate the flow state of the tiny air bubbles.Because the cavitation model is based on liquid phase change,as long as the local pressure is greater than the saturated vapor pressure of flow field,the tiny air bubble will immediately turn into the liquid phase.In the third chapter,the phenomenon of cavitation flow inside hydraulic valve is studied.After processing,the change of the relative gray value of the image is obtained.The strength of cavitation is measured according to the relative gray value.It is found that in the two-dimensional valve port model under quasi-steady flow,when the flow is cut off,local low pressure will be formed at the valve port and resulting in severe cavitation whose intensity is much higher than that under quasi-steady flow.The higher the inlet pressure is,the greater the flow inertia of the fluid will be and the longer it will take for the flow to stop.After the flow is cut off for a period of time,the cavitation strength suddenly turns from strong to weak,which is caused by the strong pressure wave returned from the outlet wall.When the pressure inside the model is stable,the gas volume proportion in the oil decreases exponentially with time under the same inlet pressure.At last,it summarizes and looks forward to the work done,and briefly introduces the research work to be carried out in the future.