Study On Mechanism Of Flow Induced Pipeline Vibration In Natural Gas Transmission Station

Due to the influence of fluid flow in the pipeline,severe vibration often occurs in the pipeline in natural gas transmission station.The vibration of the pipeline will produce strong noise and cause fatigue damage of the pipeline,which seriously threatens the safe operation of the gas transmission pipeline.In gas transmission stations,the pipe diameter is large,the pipe structure is complex,the transmission pressure is large,the flow velocity is high,and the flow in the pipe is high Reynolds number and complex turbulence.These factors make the experimental and theoretical research of fluid induced vibration of the pipeline more difficult.Therefore,the mechanism of flow induced pipeline vibration in high-pressure gas transmission stations is not clear enough,and there is a lack of necessary design criteria to prevent pipeline vibration.Vibrations still occur in some operating gas transmission stations in China.To solve this problem,this paper has carried out the following research work:(1)Aiming at the three possible vibration types of gas transmission pipeline: flow induced turbulence,flow induced vibration and acoustic induced vibration,the characteristics of these vibrations are analyzed,the research status of vibration mechanism,prevention methods and solutions are summarized,and the research direction of vibration mechanism of gas transmission pipeline is clarified.(2)Acoustic Finite Element Method is used to study the acoustic characteristics of gas in the straight pipe and the closed side branch.Combined with Acoustic Finite Element Method and solid mechanics Finite Element Method,the gas-solid coupling pipeline system vibration modal characteristics of the straight pipe and the closed side branch are studied.The influence of high-pressure natural gas on the modal parameters of pipeline system is clarified,which provides a basis for the vibration characteristic analysis of pipeline system in gas transmission station.(3)The principle and pattern of flow induced pressure pulsation in common pipeline units in gas transmission station are studied by numerical simulation method.The high-pressure natural gas flow in closed side branch,open side branch and elbow is simulated by Computational Fluid Dynamics method.The acoustic modes of gas in these pipeline structural units are studied by Acoustic Finite Element Method.Comparing flow modals and acoustic modals,it is determined whether acoustic resonance occurs in the structure is determined.The computational fluid dynamics method is used to study the flow pattern in the pipeline unit and its combination.The pipeline vibration mechanism in corresponding gas transmission stations and the effects of flow velocity,pipe diameter,transmission pressure and unit distance on flow induced pressure pulsation are clarified.The design criteria and suggestions for avoiding flow induced vibration of pipeline unit and its combined structure are put forward,which provides guidance for pipeline design of gas transmission station.(4)The advantages and disadvantages of existing methods to suppress acoustic resonance in gas transmission pipeline are analyzed.According to the mechanism of flow induced acoustic resonance and the similarity principle,the influence of the branch angle of the blind pipe on the acoustic resonance in the closed side branch is studied,which provides a practical new scheme to solve the problem of acoustic resonance.Through the research,the main conclusions of this paper are as follows:(1)As solving the problem of pipeline vibration and analyzing the vibration modal of pipeline system,for the low-order vibration modal,the coupling effect between gas and solid can be ignored.(2)The method of using DDES turbulence numerical model and hexahedral structured grid simulation to calculate the flow-induced pressure pulsation in high-pressure gas transmission pipeline is reliable.(3)The causes of pressure pulsation in different types of pipe units in the gas transmission station are different.The pressure pulsation in the closed side branch and the open side branch pipeline is mainly caused by the flow induced acoustic resonance,while the pressure pulsation in the elbow is mainly caused by the vortex shedding.(4)In the pipeline design of gas transmission station,in order to avoid acoustic resonance,the ratio of inner diameter to branch length of single closed side branch shall be greater than 0.3,and the ratio of branch inner diameter to branch centerline of open side branch shall be greater than 0.08.(5)As the angle between the closed side branch or open side branch and the main pipe is 120°,acoustic resonance can be significantly suppressed.