| With the depletion of natural resources on land,people pay more attention to the heavy oil and the ocean.The viscosity of heavy oil is too large,and the shear stress between oil and pipe wall is too large,so it is difficult to transport.At present,physical means,chemical means and biological means are mainly used to change the physical properties of oil products to achieve the effect of viscosity and drag reduction.However,the high transportation cost limits the exploitation of offshore heavy oil.In view of the existing problems,a new method of oil-water annular flow transportation is proposed.The basic principle is to add an incompatible and low viscosity liquid water between the heavy oil and the pipe wall,so that the heavy oil as the core flow is wrapped by the water ring for pipeline transportation.Compared with steel pipe,flexible pipe is easy to bend,lay,recycle and more suitable for marine environment.Based on the physical properties of multiphase fluid,the N-S equation and turbulence model are used to describe the fluid movement,the v0 f model and CSF model are used to trace the oil-water interface,the numerical equation and analysis model are established,the fluid structure coupling method combined with CFD and CSM is used to discuss the flow induced vibration of 90° flexible elbow,analyze the relationship and effect between the pipeline and two-phase flow,and compare whether there is fluid solid coupling or not The difference of cooperation.With constant velocity inlet,through the comprehensive analysis of y-axis section and elbow cross section of the whole pipeline,there is no obvious difference between the fluid solid coupling model and the non fluid solid coupling model.Quantitative analysis and comparison of the fluid solid coupling model and the non fluid solid coupling model show that the effect of the fluid solid coupling is very small,which can be ignored in the actual application process.Furthermore,considering the collision deformation of flexible pipeline,the evolution of turbulent kinetic energy and vortex structure of oil-water annular flow in the pipeline,the evolution of annular flow pattern and the evolution of pressure field are analyzed under different forms of structural deformation(0-shaped deformation with radian and V-shaped deformation without radian),different degrees of deformation(5%-30% six kinds of sag degrees)and different velocities(V1、V3 and V5,three kinds of velocities).The results show that the turbulent energy produced by the V-shaped depression is much greater than that of the zero shaped depression.When the two positions of the pipeline have structural deformation,the turbulent kinetic energy generated by the "○" shaped depression is greater than that of the "V" shaped depression,resulting in the effect of 1 + 1 > 2.No matter the structural deformation of "V" or "zero" shaped depression occurs in the pipeline,when the degree of depression is less than or equal to 30%,the fluid can still recover the stable form of oil-water annular flow after passing through the structural deformation area,and the structural deformation caused by ordinary collision will not affect the form of annular flow.In the ideal condition,the fluid characteristics of 180 ° elbow,such as volume fraction of oil phase,velocity distribution,pressure distribution and so on,are discussed.The influence of curvature on annular flow is compared,and the influence of secondary flow in 180 ° elbow is analyzed.When the fluid passes through a 90 ° bend,the oil phase is still a complete whole.When the fluid continues to pass through the bend,the oil phase is obviously squeezed by the water phase,and the oil phase is obviously divided into two halves.After the 180 ° bend,the oil phase is obviously squeezed by the water phase,causing damage.When the curvature ratio increases to 40,the annular flow can maintain its complete shape;when the velocity exceeds V3,the annular flow will still be destroyed. |
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