| People have long known the phenomenon of cavitation in liquid system,but most of the research on the phenomenon of cavitation is concentrated in water medium.At present,the understanding of the phenomenon of cavitation in hydraulic system and hydraulic component runner is limited,and the phenomenon of cavitation in hydraulic oil is one of the main reasons for the vibration,cavitation and noise of hydraulic component and hydraulic component.The phenomenon of cavitation in hydraulic system is still the same.One of the main factors that reduce the control accuracy of hydraulic system will hinder the development of hydraulic technology.There are some differences between oil medium cavitation and water medium cavitation in the mechanism and physical characteristics.Water medium cavitation is steam-type cavitation based on phase change,and hydraulic oil cavitation is air-type cavitation based on air precipitation originally dissolved in oil.Studying the cavitation flow characteristics of oil medium is of great significance to improve the existing phase change-based cavitation model,improve the stability of hydraulic system and improve the performance of hydraulic components.In view of the complex flow characteristics of oil in the three-dimensional experimental model,the difficulty of visualizing the cavitation phenomenon in the three-dimensional experimental model,the immature mathematical model of air-type cavitation based on oil medium,and the difficulty of matching experimental phenomena with theoretical research,this paper designs a two-dimensional experimental model of the valve port of the non-circular opening V-type throttle groove,which can measure the light source.With the help of high-speed camera technology and image processing technology,the cavitation phenomena of oil flowing through small opening and gradually expanding valve orifice are studied.The cavitation mechanism of oil medium is not further studied,and the mathematical model of air-type cavitation is improved to provide preliminary experimental basis.The experimental results show that there are three kinds of cavitation phenomena:attachment cavitation,cloud cavitation and atomized cavitation when oil flows through the two-dimensional valve orifice.The three types of cavitation have obvious descending relationship.Cloud cavitation is formed by attachment cavitation falling off,and cloud cavitation collapses under the action of vortices to form atomized cavitation.Attachment cavitation develops toward triangle-like shape with theincrease of pressure;when the cavitation flow enters the quasi-steady state,the oscillation behavior of cavitation volume can be divided into intermittent oscillation and periodic oscillation.The oscillation behavior of cavitation volume increases with the increase of inlet pressure,the amount of air material increases,the duration of intermittent oscillation decreases,and the periodic oscillation behavior decreases.When the inlet pressure is low(the maximum inlet pressure is 4.5 MPa),the cavitation volume increases linearly with the increase of the inlet pressure,whether intermittent oscillation or periodic oscillation.The periodic variation of the cavitation flow in the expansion section is related to the inlet pressure,intrinsic solubility,saturated vapor pressure and gas expansion mechanism.When the inlet pressure is less than 3.0 MPa,the increase of void volume is dominated by the precipitation of air dissolved in oil at low pressure,which is similar to the phase change cavitation of water.When the inlet pressure is above 3.5 MPa,the dominant role of air precipitation mechanism is weakened,while the role of air expansion mechanism caused by low pressure is enhanced,which is different from the phase change cavitation mechanism of water. |
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