Abstract

This study carried out a three-dimensional, unsteady, numerical simulation to investigate the effects of the cylinder radius, Reynolds number, three-dimensionality and unsteadiness on the mixed convection in a rectangular enclosure containing a cold circular cylinder. The variations in the cylinder radius in the range of 0.1 to 0.3 times the length of the enclosure and the Reynolds number in the range of 100 to 1000 were considered. The flow and thermal structures reached three different regimes depending on the radius of cold cylinder and Reynolds number. The patterns in the flow and thermal fields were categorized into three regimes: steady two-dimensional convection, steady three-dimensional convection, and unsteady three-dimensional convection. The temperature distribution, vortical structure, and Nusselt number for a heated bottom wall were extensively analyzed. The transition of flow regime, flow instability and the heat transfer performances were influenced by the presence of cylinder. In addition, the three-dimensional flow characteristics were quantified using orthogonal enstrophy, and the unsteady characteristics were investigated by carrying out the frequency analysis of Nusselt number. As the three-dimensionality in flow and thermal fields increases and the flow regime changes to the three-dimensional unsteady convection regime, the difference in the results of two and three-dimensional simulations also increases.

摘要

本研究进行了三维非定常数值模拟，以研究圆柱半径、雷诺数、三维度和非定常性对包含冷圆柱的矩形外壳中混合对流的影响。考虑了圆柱半径在外壳长度的 0.1 到 0.3 倍范围内的变化和 100 到 1000 范围内的雷诺数。根据冷圆柱半径和雷诺数，流动和热结构达到三种不同的状态。流动和热场的模式分为三种状态：稳定的二维对流、稳定的三维对流和不稳定的三维对流。温度分布、涡旋结构、对加热底壁的努塞尔数和努塞尔数进行了广泛分析。流态的转变、流动的不稳定性和传热性能都受到圆柱体的影响。此外，利用正交熵对三维流动特性进行量化，并通过努塞尔数的频率分析研究非定常特性。随着流场和热场三维度的增加，流态向三维非定常对流态转变，二维和三维模拟结果的差异也随之增大。三维流动特性采用正交熵量化，非定常特性通过努塞尔数频率分析研究。随着流场和热场三维度的增加，流态向三维非定常对流态转变，二维和三维模拟结果的差异也随之增大。三维流动特性采用正交熵量化，非定常特性通过努塞尔数频率分析研究。随着流场和热场三维度的增加，流态向三维非定常对流态转变，二维和三维模拟结果的差异也随之增大。