Simulation And Experimental Research Of Cavitiation In The Jet Flow Field In Pilot Stage Of A Hydraulic Servo Valve

The jet flow in the flapper-nozzle pilot stage of hydraulic servo valves has fewcharacteristics, such as small scale, high velocity and so on. Therefore, cavitationoften occurs in the jet flow field and it results in oscillation and noise of theservo-valves. It directly relates to the stability of the servo valve, thus affects theperformance of the whole hydraulic control system. In order to improve theperformance of the servo valve, it is essential to build the mathematical model ofcavitation in the jet flow field and to study the mechanism of cavitationIn this paper, the mathematical models of cavitation in the jet flow field in aservo valve are established, which is accompanied by the continuity equation ofgas-liquid mixture, the momentum equation of gas-liquid mixture, standardturbulence model, the equation of Rayleigh-Plesset and so on. The3D flow fieldmodel is established by PRO/E software.Its grid is divided and boundary conditionsare set by GAMBIT software prior to implementing of the simulation. The3D modelis simulated by FLUENT software with different inlet pressure, different outletpressure, different size of flapper and different viscosity of liquid. The appearanceof cavitation under different conditions is predicted by analyzing vapor volumepictures, velocity distribution pictures and streamline pictures of different sectionsof the3D model. The cavitation in the jet flow field is observed by a high speedcamera with different size of flapper on different condition of inlet pressure, outletpressure and temperature. The appearance of cavitation under different experimentalconditions is predicted by analyzing the photos of the jet flow. The experimentalresults are compared with the simulation.In this paper, the mathematical models of cavitation in the flapper-nozzle pilotstage of a hydraulic servo valve are built based on the fluid mechanics andcavitation theory. The finite element analysis and visualization research of jet flowfield in pilot stage of servo valves are carried out. The occurring mechanism and lawof cavitation in the jet flow field are summarized. These works provide some theorybasis for the research of the relationship between cavitation and the high frequencynoise.