Investigation Of Cavitation Flow Characteristics In The Regulating Valve

The regulating valve is used in the hydraulic system to control the pressure,flow flux and flow direction of the fluid,which is the largest number of varieties,most widely used and most flexible component in hydraulic technology.The precise design and energy-saving control of regulating valves depend on the understanding of cavitation flow and relative mechanics in the flow channel.The varies in flow state and spatial position of the cavitation flow characterized by local low pressure will change the flow in the regulating valve,which will cause cavitation,vibration and noise of the valve spool and seat,then affecting the reliability and stability of the valve control.Because the cavitation flow is closely related to the complex phenomenon such as turbulence and vortex,and the structure of flow channel in the regulating valve is complicated and the velocity is high,the current research only stay at some theoretical hypothesis and empirical experimental conclusion.Therefore,combining with theoretical analysis,flow simulation and experimental visualization,our paper focus on the cavitation flow characteristics in the regulating valve and its influencing factors,and the optimization project of the regulating valve is proposed to improve the anti-cavitation bubble ability and accurate control of the regulating valve.Combing orifice throttling principle,continuity equation in hydrodynamics,Bernoulli equation,the relationship between valve opening degree and its flow rate is analyzed.Based on the technological parameter,structure size and operational condition of coal liquefaction regulating valve,the geometric calculation model is established and the basic control equation and boundary conditions are chose.CFD numerical calculation is used to obtain the key parameters such as velocity,pressure,volume fraction of gas and liquid phase and turbulence energy in the regulating valve under typical working condition and geometric structural parameters,so cavitation flow characteristics in regulating valve could be obtained.A high-speed camera is used to capture the cavitation flow in the regulating valve,and the correctness of cavitation model in the regulating valve and the reliability of Fluent numerical simulation are both confirmed.Combining with theoretical analysis,flow simulation and visualization,the cavitation flow characteristics in the flow channel under different throttling orifice are accurately obtained.Characteristic parameter such as velocity,pressure,gas volume fraction and turbulence energy is proposed to describe the cavitation flow in throttling orifice.High reflux in cavitation zone near the throttling orifice will results in cavitation bubble and cavition erosion.Furthermore,the influence of structural of valve spool and seat on the gas-liquid two-phase flow inside the regulating valve are also investigated,and we pointed out that combining the optimized valve spool and seat could reduce the degree of flow separation and depress cavitation flow inside the hydraulic valve.The working conditions mainly include inlet and outlet pressure differential and opening degree.The influence of working conditions on cavitation flow is analyzed by numerical simulation.When the inlet and outlet pressure differential is unchanged,the greater the opening degree of the regulating valve,the weaker the flow resistance and viscosity of the oil,then higher velocity and larger range of low pressure.With the decrease of the reflux area near the spool head,the axial length of the cavitation area is decreased,and the turbulence energy is also diminished,which will lead to the weaker cavitation flow.Furthermore,keep the opening degree unchanged,the larger the inlet and outlet pressure differential,the greater the pressure difference and the velocity gradient at the valve orifice,the smaller the minimum pressure in the flow field,the larger the axial length of the cavitation area,and the more intensity turbulence energy,which will result more severe cavitation flow.Based on the idea of suppressing cavitation flow,working conditions such as small opening degree and large pressure differential should be avoided.The geometric structural parameters mainly include the radius of spool head,the channel length downstream and expansion angle of vavle seat.The slight change of them will lead to a significant change in the cavitation flow.The influence of geometric structural parameters on cavitation flow is analyzed by numerical simulation.Based on the prediction method proposed in our paper,decreasing radius of spool head could reduce the velocity of the reflux and the cavitation intensity,and the turbulent kinetic energy in the flow channel is also reduced,so the cavitation flow could be suppressed effectively by reducing the radius of spool head.The longer the channel length downstream of the valve seat is,the short the length and velocity of the reflux are,the longer the axial length of the cavitation area is,and the higher the turbulent kinetic energy is,which induce intensity cavitation flow.The increase of expansion angle of vavle seat promotes the development of oil velocity in the downstream channel and decreases the cavitation area.Therefore,proper geometric structural parameters in engineering is helpful to cavitation supression,so as to extend the service life of the regulating valve.In conclusion,the investigation on the cavitation flow characteristics of the regulating valve could provide theoretical guidance to optimum structure of the regulating valve,accurately control the flow rate of the regulating valve,increasing anti-cavitation ability and energy saving,noise reduction etc.Furthermore,the results in our paper could also be extended to the analysis of multi-phase flow in the regulating valve,structural optimization design,local strengthening treatment and other safety assurance projects,which have significant economic and social benefits.There are 98 figures,3 tables and 135 references in this paper.