Study On Flow And Erosion Characteristics Of Ice-Water Two-Phase Flow

Pipe plays an important role in water transportation and oil transportation in ocean engineering.Under low temperature conditions,the pipe is often disturbed by fine crushed ice crystals.The ice crystal particles are mixed into the pipe,which tends to cause ice accumulation in the pipe.The fine ice crystals are mixed into the pipe and easily cause erosion.The coarse-grained ice crystals are mixed into the pipe and easily lead to pipe resistance.Reducing the impact of ice crystals on erosion of pipe and preventing ice accumulation in pipe have become a hot topic.Based on computational fluid dynamics(CFD)and discrete element method(DEM),the flow characteristics in straight pipe,erosion in elbow and ice accumulation characteristics in straight pipe are studied in this paper.The main research contents are as follows:(1)Based on computational fluid dynamics(CFD)and discrete element method(DEM),the CFD model for liquid flow and the collision model of particles in pipe are established.The flow in straight pipe is validated by CFD-DEM coupling method,which verifies the accuracy of the numerical simulation method for flow in straight pipe.(2)CFD-DEM coupling method is used to study the flow characteristics of ice-water two-phase flow in the straight pipe.The flow pattern,resistance characteristics and flow field variation were mainly studied.The effects of four parameters which include velocity,particle diameter,volume fraction and incident angle about flow pattern,resistance loss and flow field are analyzed.The results show that the change of static bed flow,moving bed flow and suspended bed flow is related to velocity,volume fraction and particle diameter.The incident angle of particles has little effect on the transition of flow state.The faster velocity,larger particle diameter and higher volume fraction will cause pressure drop of pipe higher,but when the particle diameter distribution of particles from narrow to wide,the pressure drop first decreases and then increases.The single particle diameter and velocity have great influence on the flow field.Particle diameter distribution and volume fraction have little effect on the flow field.(3)Based on CFD model,the effects of Stokes number,particle diameter distribution,velocity,particle shape and elbow properties on erosion characteristicsare analyzed.The maximum penetration rate and the maximum erosion area are analyzed.The results show that the Stokes number,particle diameter distribution,velocity,particle shape,and elbow arrangement have a great influence on the maximum erosion area;Compared with single particle diameter,the particle diameter distribution has a smaller erosion penetration rate to the pipe.The higher velocity,the larger particle shape coefficient,the lower roughness,the lower hardness of the elbow,and the lower R/D ratio will cause greater penetration rate.The arrangement of the elbow also has a certain influence on the penetration rate.(4)Using CFD-DEM coupling method to study characteristics of ice accumulation in straight pipe,considering the influence of coarse particle ice velocity,particle diameter and particle shape on the position and degree of ice accretion,and analyzing the aggregation of fine particles in straight pipe at different velocity.The results show that for coarse-grained ice,the higher velocity,the smaller particle diameter will cause less ice accumulating in the pipe.The needle-shaped particles in the six particle shapes are most likely to cause ice accretion and stacking in pipe;For fine ice crystals,as the velocity increases,the number of fine particles gather at the outlet pipe section decreases,and the volume of aggregated particles is smaller.