Erosion Characteristics Analysis Of Sandy Pipelines By Considering Liquid-solid Bidirectional Coupling Effect

A certain amount of particles are mixed in the fluid of pipelines conveying fluid to form the liquid-solid two-phase flow,as the solid sand moving with the fluid continuously washes the surface of the pipeline,erosion problems such as slight deformation,cracking or even spalling gradually occur on the surface of pipelines.This kind of erosion damage will cause problems such as performance degradation,aging and shortened service life of the pipeline,which will threaten the safe operation of the pipeline system.Taking the sandy pipeline as the research object,the flow characteristics of the continuous phase fluid is solved in the Euler coordinate system,and the movement trajectories of the discrete phase of sand particles is solved in the Lagrange coordinate system.The calculation process considers the interaction between the moving fluid and solid,and realizes the bidirectional coupling between the fluid and solid.The effects of fluid flow parameters and structural parameters of the pipeline on the erosion are mainly studied,and the erosion characteristics of the single sand particles on the pipeline is analyzed from a microscopic perspective.The main contents and results are as follows:?1?The computational fluid dynamics software FLUENT was used to establish a numerical calculation model for erosion of sandy pipelines.The work aims to study flow characteristics of the fluid in the pipeline.Results show that the pressure gradually decreases from the outer wall to the inner wall and exhibits a gradient distribution in the central section of the pipe elbow.The inside of the junction of the pipe elbow and the straight outlet pipe decreases sharply,forming a vortex stagnation zone.The sand trajectory in the vertical pipe section is spiral.?2?The erosion characteristics of the pipeline when the sand particle size distribution range is Rosin-Rammler distribution and constant distribution are compared and analyzed.Results show that the maximum erosion rate of the Rosin-Rammler distribution is 4.39×10^-7kg/?m²·s?,and the maximum erosion rate ratio of the constant distribution is 3.54×10^-7kg/?m²·s?,therefore,the maximum erosion rate ratio of the constant distribution is 19.4%lower than that of the Rosin-Rammler distribution.?3?The effects of flow characteristics?velocity,sand diameter,sand mass flow?and pipeline structural characteristics?pipe diameter,curvature radius,pipeline placement direction?on the erosion rate are investigated,and the erosion mechanism was analyzed.Results show that,when the flow velocity reaches 3m/s,the erosion damage location of the pipeline moves from the bottom of the straight pipe section to the junction of the outlet of the pipe elbow and the straight pipe section.There is a critical value of 0.21 kg/s for the mass flow rate of sand particles.When the critical value is lower than the critical value,the maximum erosion rate of the pipeline increases with the increase of the sand flow rate.After exceeding this critical value,the impact of the sand flow rate on the erosion rate of the pipeline is no longer significant.With the sand size smaller than 320?m,there is no obvious relationship between the maximum erosion rate and the sand size.As the sand size continues to increase,the maximum erosion rate of the pine wall increases.As the curvature radius of the pipe elbow increases,the position of severe erosion damage of the pipe wall is turned from the inner wall surface of the elbow part to the outer wall surface.Correlation analysis of different erosion influencing factors with MATLAB software,which found that the fluid velocity and sand mass flow are the main factors causing erosion of pipelines.?4?The impact behavior of single sand particle on the pipeline is studied by the software ANSYS Workbench.Results show that the impact depth and Von Mises stress of sand particles increase with increasing impact speed,impact angle,sand particle size and number of impacts.When impacted at a small angle,the sand particles make a cutting motion on the surface of the pipe.The impact depth of the cubic sand particle is always greater than spherical sand particles.When the impact velocity of the sand particle is 36m/s,the maximum erosion depth of the cubic sand particle is 8.79?m,which is 2.87 times the spherical sand particle.