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A Finite Element/Smoothed Profile Method for Flows and Heat Transfer with Complex Boundaries

Author: WangZhiCheng
Tutor: TangDaWei
School: Graduate School,Chinese Academy of Sciences
Course: Engineering Thermophysics
Keywords: Finite Element Adaptive Mesh Parallel Computing Entropy ViscosityStabilized Method Large-Eddy Simulation Immersed Boundary Method SmoothedProfile Method Flat-tubes Convective Heat transfer
CLC: TK124
Type: PhD thesis
Year: 2013
Downloads: 43
Quote: 0
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Abstract


Engineering flows are characterized by high Reynolds number, complicated boundary conditions. It is necessary to develop simulating software to overcome the deficiency which is often encountered by using commercial software. We developed a general finite element code which could compute2d/3d unsteady incompressible flow and heat transfer, in the framework of open source library DEAL.Ⅱ. We also introduce entropy viscosity stabilized method and smoothed profile method to overcome the instability of numerical integrating and difficulty of handling of complex boundary condition.The first part of this work is focuses on the development of a simulating tool that can predict incompressible flows as well as heat transfer. We use incremental projection method to decouple the velocity and pressure. One feature of current simulating software is it can improve the accuracy by increasing the degree of basis function or refining the mesh adaptively. In order adapting diversity of real problem, the software has interfaces to handle different kinds of boundary condition and initial condition. In order to accelerate the solving procedure, the simulating tool supplies two ways of parallel computing. For the convenience of users, we also implement several post-processing tools and parameter-handling functions.We introduce a stabilized method based on numerical entropy generation. This method calculates artificial nonlinear viscosity from the ideology of maintain kinetic energy of discrete equation. When applying entropy-viscosity stabilized method to cavity flow and flow past a circular cylinder, we found this method not only increase the integrating stability, but also improve the accuracy. Whereas artificial viscosity plays a same role as turbulent model on simulating, it is applied to modeling turbulent flow. After a tiny modify of the value of entropy viscosity compared with that in stabilized method, an entropy viscosity based model is applied to fully developed turbulent channel flow at Reτ=180. The results show it is capable to predict wall bounded turbulent flows.Inherently, FEM is capable of simulating flows with complex geometries, but this ability is based on the quality of meshes. There is possibility that it could not generate a body-fitted mesh, when the computing domain is too complex or the boundary is just moving. To solve this difficulty, we introduce a so called smoothed profile method, which is proposed recently. Different from conventional numerical method, SPM solves the equations both on fluid domain and solid domain, the effect of immersed boundary is treated as a body force which is applied to the governing equations. We implement the SPM in the framework of FEM with adaptive mesh refinement. Combined with entropy viscosity based stabilized method, we extend the SPM to modeling flow and heat transfer at high Reynolds number.The last part of current work is investigating air-side heat transfer characteristics of flat-tubes bundle and flows generated by electric fans, by using the numerical method mentioned above. The simulating results shows:it is preferable to set gap width in the range of2.0-3.0times minor axis of the tube; tranverse oscillating is not necessarily to enhance heat transfer, since oscillating can increase the interferance between adjacent tubes; Electric Fans are acted on oscillating forces on axis direction.-

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CLC: > Industrial Technology > Energy and Power Engineering > Thermal engineering, heat > Thermal Engineering Theory > Heat Transfer
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