Study On The Influence Of Valve Regulation On The Flow Stability In The Pipe-valve Component

Pipe valve component include process valves and their upstream and downstream pipeline,which carry fluid control and transmission functions,and are widely used in process industries such as petroleum and chemical.Under different regulation functions(steady regulation and transient regulation)of the valve,unstable flow will occur in the valve due to the throttling effect.This unstable flow will develop along the downstream of the pipeline,and the developing unstable flow will affect the collection of stable metering signals by the flow metering equipment,thereby restricting the accurate metering of the fluid.This thesis takes the gate valve with a simple structure as the control object,and conducts the research on the influence of the internal flow stability of the pipe valve component under the control of the valve.Through the analysis of the internal flow characteristics of the pipe valve component,it is proposed that the internal flow of the pipe valve component develops from unstable flow to The stable flow characterization method provides theoretical support for revealing the internal flow characteristics of the pipe valve component and the accurate installation and positioning of fluid metering equipment.The main research contents are as follows:(1)Establish a physical model of the internal flow field of the pipe valve component with the flat gate valve as the control object.In order to ensure the full development of the flow,the pipes before and after the valve are extended by 10 times and 20 times the pipe diameter.Solid Works software was used to model the structure of the gate valve model,and ICEM software was used to mesh the overall flow channel under steady-state and transient control,and the corresponding grid independence verification was carried out.An experimental platform for the external flow characteristics of the pipe valve was built to collect the flow rate and the difference in the pipe valve at different steady-state opening degrees(20%,50%,and 80%)and different transient opening and closing control times(10s,25 s,and 50s).The pressure value of the monitoring point in the downstream of the pipeline is verified by the experimental uncertainty analysis to verify the reliability of the experimental data.(2)Research on flow stability under steady-state regulation: The valve flow coefficient increases with the opening degree,indicating that the valve’s throttling effect gradually decreases.The discharge coefficients of the experiment and the numerical simulation are in good agreement,indicating that the numerical simulation results are reliable.Carry out the numerical simulation of the internal flow of the downpipe valve component with different opening degrees(20%,50% and 80%corresponding to small opening,medium opening and large opening respectively).Analysis of the distribution characteristics of pressure,velocity and vorticity at different openings reveals that the sudden change in the flow area of the valve at small openings causes the strong pressure gradient at the valve throat to induce the generation mechanism of eccentric jets.The velocity profile and cross-section of the pipeline behind the valve are analyzed.The value distribution changes with the development of the downstream flow of the pipeline;the dimensionless parameter-velocity eccentricity is established to characterize the flow stability of the flow development along the pipeline valve.The results show that under different openings,the flow development of velocity eccentricity along the course shows a trend of gradual exponential decrease,and gradually increases to a value of 0.2.This phenomenon indicates that the internal flow of the pipe valve under the valve throttling effect develops along the way,and gradually obtains a uniform velocity distribution,that is,the internal flow stability of the pipe valve gradually increases.In addition,to obtain an equal velocity eccentricity value,the required stable flow length under a small opening degree,that is,the longer the pipeline length from unstable flow to stable flow.(3)Research on flow stability under transient control: Combining the UDF function(user-defined function)in Fluent and dynamic grid technology,the valve opening and closing time(10s,25 s and 50 s corresponds to 5mm/ s,2mm/s and 1mm/s)the flow field of the valve assembly has been numerically simulated.In the opening process,the flow coefficient increases slowly when the opening is small,and the middle opening increases faster;the flow coefficient in the closing process decreases rapidly when the opening is in the middle.The experiment and the numerical simulation are in good agreement with the flow coefficient,indicating that the numerical simulation results are reliable.The dynamic evolution process of the internal pressure,velocity and turbulent kinetic energy of the pipe valve component is analyzed,and the influence of the opening and closing process on the internal flow stability is compared.The results show that the opening and closing time of the valve has little effect on the change of the internal flow field of the pipe valve component.Comparing the opening and closing processes at the same time,the maximum value of the turbulent kinetic energy of the flow field appears at 10% of the opening during the opening,and the turbulent kinetic energy has the widest distribution range at 50% of the opening;the turbulent kinetic energy is also at 50% of the opening during the closing process The lower distribution range is the widest.Establish the turbulent kinetic energy changing rate to analyze and characterize the internal flow stability of the pipe valve component.Through the analysis of the turbulent kinetic energy changing rate along the way,it can be seen that during the opening process,the turbulent kinetic energy changing rate at 0.5T at the same pipe position is greater than that at other times.It shows that during the process of valve opening from 40% to 50%,the turbulent kinetic energy change rate of the same pipe position is relatively large,and it is the most difficult to reach a steady state.During the valve closing process,the turbulent kinetic energy changing rate at 0.6T is greater than the turbulent kinetic energy changing rate at other times,indicating that during the valve opening process from 50% to 40%,the turbulent kinetic energy changing rate at the same pipe position is larger,the most difficult to reach a steady state.