Study On Numerical Methods And Separation Characteristics Of Axial Flow Cyclone

China has abundant deep-water natural gas resources.The exploitation of these resources has strategic significance for safeguarding China's energy security.The production of natural gas wells usually contains condensate.If the natural gas condensate can be separated under the sea,gas hydrate formation which may cause pipeline blockage can be avoided and the risk of slug flow during pipeline transportation can be reduced.Therefore,the study of underwater gas-liquid separation technology is significant for the safe transportation of natural gas within pipelines.In order to realize the high-efficiency separation of natural gas condensate,the mathematical model,numerical methods,separation characteristics and optimization method for axial flow cyclone were systematically studied in this dissertation,which can contribute to the safe transportation of natural gas pipeline.First,a mathematical model including sub-models for gas,droplets and liquid film was established based on the Euler-Lagrangian approach and surface film model.The gas core was described by the Euler-Lagrangian approach,while the liquid film flow was solved by the surface film model.The proposed model can accurately describe the separation processes inside axial flow cyclone,which includes complex phenomena such as the deposition of droplets on the wall(formation of a liquid film),the flow of the liquid film,and the entrainment of droplets.In order to improve the computational efficiency and enhance the stability of calculation process,an efficient and robust pressure-velocity coupling algorithm,called IDEAL(Inner Doubly-Iterative Efficient Algorithm for Linked-Equations),was developed based on arbitrary polyhedral grids.The numerical results demonstated that the convergence and robustness of the IDEAL algorithm are superior to those of SIMPLE and SIMPLEC algorithms under different grid numbers,inlet velocities,and turbulence models.Based on the proposed mathematical model and numerical method,a solver for simulating the separation process of axial flow cyclone was developed in the framework of open source CFD software--OpenFOAM.First,the Reynolds stress model was used to simulate the pure gas flow,and the gas distribution characteristics inside the cyclone were analyzed.Then,using the Euler-Lagrangian approach and surface film model,the gas-liquid two-phase flow inside the cyclone was simulated and the relevant characteristics were analyzed.Furthermore,the effect of blade structural parameters on separation performance of axial flow cyclone under high pressure was studied in detail.Finally,a novel multi-objective optimization method was presented by combining numerical simulation,support vector machine with Nondominated Sorting Genetic Algorithm II(NSGA II).Then,the proposed optimization method was used to optimize the guide vane of cyclone.The Pareto optimal solutions for the guide vane of axial flow cyclone are obtained,which can provide important theoretical guidance for the decision makers to choose the appropriate parameters of guide vane.