Transient Numerical Simulation And Experimental Study Of Ball Valve Opening And Closing Process

With outstanding advantages such as simple structure,low starting torque and good sealing performance,ball valve is widely used in many fields of industry and life.It plays an important role in blocking equipment and piping systems,regulating pipeline flow,preventing backflow and controlling flow direction.When the ball valve adopts the V-spool channel structure,it also has the function of equal percentage flow regulation,so that the size of the pipeline flow can be precisely adjusted.Research V-sector ball valve opening and closing process valve internal flow law,analysis of the ball valve closed caused by the change in water impact pressure,is conducive to improve the ball valve design methods and improve the operational reliability of the ball valve.Based on the combination of flow interruption capability experiment and numerical simulation,this paper systematically studies the transient process of opening and closing of large-scale ball valves for nuclear power and the water hammer phenomenon caused by different closing times and different closing methods of the ball valves.The main research in this paper and the results obtained are as follows.(1)Based on the turbulence problem of U-bend published by Stanford University,the applicability of four common turbulence models and Wray Agarwal turbulence model in bend flow was studied by using computational fluid dynamics method.The results show that the SST k-ω and Wray-Agarwal turbulence models are closer to the experimental data than the standard k-ε,RNG k-ε,and Spalart-Allmaras turbulence models for numerical simulations in bend,providing a reference for the choice of turbulence models for the transient numerical simulation of ball valve.(2)Based on different driving voltages(323V,380 V,418V),the opening and closing process of the H2Q947Y-25P(DN350)electric ball valve for nuclear power was carried out flow interruption capability experiments.The experimental data was statistically processed,and the experimental results were discussed analysis.The results show that the time course of the flow and the time course of the differential pressure before and after the valve are highly reproducible when the measurement is repeated three times for the opening and closing process of the ball valve based on different drive voltages.This confirms the stability of the experimental circuit system,the reliability of the measurement system and the measurement results.The measurement standard uncertainty of the experimental data such as differential pressure was determined by calculation.The MATLAB software was used to fit the experimental scatter data to curve equations and to determine the boundary conditions for the numerical simulation of the ball valve.(3)The transient opening and closing process of the ball valve is numerically simulated based on the sliding mesh method and variable boundary conditions.The variation of the differential pressure between the inlet and outlet and the flow resistance characteristics with the relative opening degree of the ball valve during opening and closing is studied.The velocity distribution,streamline distribution,pressure distribution and the development of the vortex core pattern inside the spool of the ball valve are analyzed at different opening and closing degrees and at different cross-sectional positions.The results show that whether in the ball valve opening or closing process,through the numerical simulation of the ball valve inlet and outlet pressure difference,the flow resistance coefficient with the relative opening changes and the experimental curve basically coincide.And its value decreases as the relative opening of the ball valve increases.Reducing the relative opening of the ball valve will lead to more complex vortex nuclei in the flow channel of the spool.Under the same opening degree,there is little difference in the shape of the vortex core in the valve core flow passage during the opening and closing of the ball valve.The distribution of the internal flow field of the ball valve is obtained through numerical simulation,which reveals the variation of the differential pressure and flow resistance characteristics of the ball valve and the relative opening degree,and provides a theoretical basis for the optimal design of the ball valve.(4)Based on the sliding grid and the method of the Fluent-Expression editor to control the speed,the influence of different valve closing time and valve closing methods on the water hammer phenomenon caused is analyzed,and effective measures to prevent water hammer are proposed.The results show that: based on the constant-speed valve closing,the longer the valve closing time,the smaller the maximum water hammer pressure.A suitable extension of the valve shut-off time will help to reduce the risk of water hammer.The uniform velocity shut-off valve causes the smallest maximum water hammer pressure of any of the different shut-off methods,while the linear uniform deceleration shut-off valve increases the maximum water hammer pressure while reducing the time of water strike wave fluctuations.