弯道中流体流动及对流换热的数值模拟

发布时间：2018-01-01 09:22

本文关键词：弯道中流体流动及对流换热的数值模拟　出处：《华东理工大学》2016年硕士论文　论文类型：学位论文

【摘要】：本文以弯道中的牛顿流体和非牛顿幂律流体的流动与对流换热问题为研究对象,采用高精度算法进行了数值模拟。网格独立解是对流换热数值研究的前提,而边界条件的恰当处理则是模拟结果准确性的关键,本文着重分析了速度场和温度场的网格独立解。针对牛顿流体湍流流动,本文结合第二类边界条件(热流密度条件),并改变网格密度,对比分析其两种边界处理方式对数值解准确性的影响。对于幂律流体层流流动,本文分析了Dn数、流动指数n和Pr数对流动及对流换热的影响。对于牛顿流体和幂律流体,本文算法均良好地模拟了弯道中流体的流动与对流换热。网格独立解的研究结果表明：由于不可压缩流动中速度场和温度场之间的耦合关系较弱,获得网格独立解所需的网格数目存在差别,温度场对网格密度要求更高。另外对于幂律流体而言,当二次流出现四涡结构现象后,流动更为复杂,这种情况下,速度场对网格密度要求相对较高。对于牛顿流体湍流流动,两种热流密度边界条件的处理方式的对比结果表明,Kader(1981)的代数方法可以在网格粗糙的情况下仍然能够较好地吻合实验值,具有更好的通用性和网格适应性。但由于壁面处温度梯度对于计算Nu数的准确性有较大的影响,此时仍应尽可能采用y+值小的网格。对于幂律流体层流流动,尽管Dn数具有不稳定性,二次流从二涡突变成四涡结构时的Dn数不固定,但当四涡结构现象出现后,相同的Dn数下,本文速度场分布与前人结果吻合良好,且随着Dn数增大,其对速度场影响减弱；而温度场分布主要受到Dn数和Pr数的影响。
[Abstract]:In this paper, the flow and convection heat transfer problems of Newtonian fluid and non-Newtonian power-law fluid in curved channel are studied, and the numerical simulation is carried out by using high-precision algorithm. The independent solution of grid is the premise of the numerical study of convection heat transfer. The proper treatment of boundary conditions is the key to the accuracy of the simulation results. In this paper, the grid independent solutions of velocity field and temperature field are analyzed, especially for the turbulent flow of Newtonian fluid. Combining the second kind of boundary condition (heat flux condition), and changing the grid density, the effect of two kinds of boundary treatment methods on the accuracy of numerical solution is analyzed, and the laminar flow of power law fluid is studied. In this paper, the effects of Dn number, flow exponent n and pr number on flow and convection heat transfer are analyzed, for Newtonian fluid and power law fluid. The numerical results show that the coupling relationship between velocity field and temperature field in incompressible flow is weak. There are differences in the number of meshes needed to obtain the independent solution of the grid, and the temperature field requires higher grid density. In addition, for power-law fluids, the flow becomes more complex when the secondary flow has a four-vortex structure phenomenon. For the turbulent flow of Newtonian fluid, the results of two heat flux boundary conditions are compared. The algebraic method of Kaderian 1981is able to agree well with the experimental data even when the grid is rough. It has better generality and mesh adaptability, but the temperature gradient on the wall has a great influence on the accuracy of the calculation of Nu number. In the case of laminar flow of power-law fluid, the number of Dn is not fixed when the secondary flow changes from two vortices to four vortices, despite the instability of Dn number. However, when the phenomenon of four-vortex structure appears, the distribution of velocity field in this paper is in good agreement with the previous results under the same Dn number, and with the increase of Dn number, its influence on the velocity field weakens. The distribution of temperature field is mainly affected by Dn number and pr number.
【学位授予单位】：华东理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK124

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