U形弯道中湍流对流换热的数值模拟

Numerical Simulation of Turbulent Convective Heat Transfer in a U-Bend

网格独立解是湍流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。结合方形截面U形弯道中的湍流对流换热,采用SSTk-ω模型对弯道内流场和温度场进行计算,重点分析了速度场和温度场的网格独立解。同时结合第二类边界条件(热流密度条件),对比分析其两种处理方式对数值解准确性的影响。结果表明,由于不可压缩流动中速度场和温度场之间较弱的耦合关系,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。热流密度边界条件的两种处理方式的比较表明,Kader(1981)的代数方法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。

The grid-independent solution is a premise of numerically studying turbulent convective heat transfer,while the appropriate treatment of boundary conditions is critical to the accuracy of numerical results.In this paper,turbulent heat transfer in a squared U-bend is studied with the SSTk-ω model.The flow and temperature fields are calculated,and the grid-independent solutions of velocity and temperature fields are analyzed emphatically.Under the second type of boundary condition（heat flux condition）,the influence of two treatments on the accuracy of numerical solutions is contrastively analyzed.Because the coupling of velocity and temperature fields is weak,the mesh size required for grid-independent solutions is different for the two fields.A finer mesh is needed for the grid-independent solution of the temperature field.The comparative analysis of the two treatments of the heat flux condition demonstrates that the algebraic formulation of Kader（1981）is in good agreement with experimental data even though the mesh is relatively coarse,so it has better versatility and grid adaptability.