Investigation Of Fluid Induced Vibration Characteristics Of U-type Bend Based On Bidirectional Fluid-Solid Coupling

The two-phase fluid in U-type tube that is used in basic flow and heat transfer components is subjected to centrifugal force and the pressure difference of interphase interface to produce a complex and variable flow pattern,which induces pipe vibration.U-tube vibration has an important impact on the pressure drop heat transfer and safe operation of the heat exchanger.Different flow patterns and flow parameters have large differences in the induced vibration characteristics of the pipe.Therefore,the flow characteristics of two-phase flow in the U-tube and fluid-induced pipe vibration are studied can provide important theoretical basis for the design and safe operation of U-tube heat exchange equipment.Based on the above problems,this paper's research is carried out on pipeline vibration induced by gas-liquid two-phase fluid in the tube.The main conclusions are as follows:The vibration intensity of the gas-liquid two-phase flow in the U-tube is,in descending order,slug-wave flow,ring-wave flow,and ring-dispersion flow.The acceleration vibration response of the pipeline is all in the form of low frequency beat of 18-20 HZ.In the slug-wave flow,the effusion in the elbow is serious,and the slug in the upstream segment of the pipeline is fully developed.As the liquid phase breaks through the bend,the upstream pressure of the pipeline is released,and the slug flow in the upstream section disappears.Due to the existence of large phase interface shear forces in the downstream of the pipeline,the wave flow develops,and stronger vortex generation and dissipation phenomena occur in the pipeline.with the flow state at the bend is stable,the wave flow at the outlet of the pipeline weakens,and gradually spread to a longer range of the pipe downstream of the pipeline;In annular-wave flow,the pipeline operation is divided into three phases:liquid phase accumulation,liquid phase breakthrough,and stabilization.Liquid phase accumulation occurs at the inlet of the pipe bend.Due to the large gas phase velocity,the liquid phase breaks through quickly and the bend is formed.Annular flow,due to the pressure difference and centrifugal force caused by the apparent velocity of the liquid and gas phases,a symmetrical Taylor vortex is formed at the bend,a single-core vortex structure exists in the pipeline at the development of the waveform flow,In the later period of pipeline operation,the wave flow in the downstream of the pipeline is well developed;When the flow pattern of the pipe is annular-dispersive,the liquid phase in the pipe has no liquid accumulation at the entrance of the pipe due to the strong liquid-carrying capacity in the pipe.As the pipe runs,the liquid film at the pipe is thickened,and liquid exits at the pipe exit.Flow characteristics that induce diffuse flow downstream of the pipeline.The two-phase flow-induced vibration in the pipe mainly manifests as the beat of low-frequency vibration in the in-plane direction,and the main frequency of the pipe vibration is concentrated near the third-order natural frequency.The pipe has a strong vibration response in the Z direction,followed by the Y direction.Different axial monitoring points of the pipeline have similar vibration response spectrum distribution forms,which are symmetrically distributed in a parabola.The vibration intensity is maximum at the bend.The effect of the gas phase apparent velocity U_g on the vibration intensity of the pipeline is gentler when the liquid phase apparent velocity U_l is smaller or unchanged;when U_l is larger,the effect of U_g on the vibration intensity of the pipeline increases significantly,and the flow state in the tube is segment When the plug-wave is flowing,the performance is strong;when U_g is constant or smaller,the effect of U_l on the vibration intensity of the pipeline is the same as the former;With the increase of U_g,the influence of U_l on the vibration intensity of the pipeline showed a secondary growth relationship.When the liquid phase apparent velocity is small,the vibration response of the pipeline increases slightly with the increase of?.With the increase of the liquid phase apparent velocity,the pipeline vibration changes with?.The increase of ?^RMS starts early,and the vibration intensity of the pipeline increases sharply.