Research On Cavitating Flow Characteristics In Hydraulic Throttling Valves

In this paper，characteristics of internal cavitation flow in (two-step) throttle valvewith difference pressure between import and export, opening, the fluid medium, seatparameters have on are studied by numerical and experimental methods.According to the structure of throttle valve and characteristics of cavitation flow,axisymmetric numerical calculation model of cavitating flow is established. Combinedwith dicrete method and the finite method for flow algorothm, numerical model equations,boundary conditions and meshing programs and mesh schemes are established andanalyzed.The influence of the difference pressure between inlet and outlet, the opening of the(two-step) throttle valve and the kind of fluid on cavitation flow in throttle valve wereanalyzed. The variations of pressure, velocity distribution, the flow lines, cavitationdistribution were discussed. The results shows that: Cavitation region is mainly distributedin the downstream of the orifice, the more serious cavitation region mainly in the edgeregion of the recirculation zone in contact with the high velocity region. Cavitationintensity is also affected by the size of the recirculation region and circumfluence centerposition, and the size and distribution of the recirculation zone is mainly effected by theliquid flow direction and its velocity. Moreover，cavitation region increases with increasingof the difference inlet-outlet pressure. Cavitation region increases first and then decreaseswith the decrease of the opening. In other words, with the decreasing of opening, thecavitation region increase when opening is larger and the cavitation region decrease whenthe opening almost closed. Characteristics of cavivation between the water and hydraulicoil in throttle valve were analyzed comparatively, the anti-cavitation performance ofhydraulic oil is better. In addition, Cavivation flow between the three kinds of structures oftwo-stage throttle valve model was analyzed comparatively，and the program whoseupstream of orifice is smallest have a good anti-cavitation performance.The experimental investigation of cavitation flow in hydraulic valve anslysis based onhigh speed photography is also studied. It contains: optical system, hydraulic system andexperimental platform. The transparent thorottle valve has been designed; thecorresponding hydraulic components and optical components also have been selected andthe cavitation experimental setup was build. Using high speed camera, the influence of theopening on flow velocity and cavitation are studied. The results show that cavitation phenomenon almost invisible in the throttle valve when opening is larger. With thedecreasing of opening, the maximum velocity and cavitation region increase, on thecontrary, decrease when the opening almost closed. The experimental results approxi--mately agree with numerical simulation results.