Effect of dimple depth on turbulent flow and heat transfer of kerosene in rectangular duct

凹陷窝深度对矩形通道内煤油流动与传热性能的影响研究

In this paper,the coupling effect of dimple depth and fluid properties on convective heat transfer of kerosene flowing in a smallscale rectangular duct with circular dimples is studied numerically.The numerical simulation is based on Reynolds average method with a shear stress transport(SST)k-ωturbulence model and a 10-components surrogate model of kerosene.Turbulent flow and heat transfer properties in different depths of circular dimples are obtained.The results show that the three-dimensional vortices are generated by dimples and the vortices alter local turbulent flowing significantly,leading to both enhanced and reduced convective heat transfer to the wall at different locations.It is also found that the averaged Nusselt number on different dimpled walls first increases in the raising of dimple depths and then decreases after dimple depths reach a certain value.The obtained flow field shows that the heat transfer enhancement on the dimpled wall is caused by vortices with horse-shoe and tornado structures.When dimple depth further increases,the vortical structure changes to asymmetric horn spiral form,which causes heat transfer reduction.Similar to the variation of Nusselt number,the friction factor through dimpled duct also increases firstly with the dimple depth and then decreases.

摘要本文通过数值仿真研究了凹陷窝深度和煤油物性的变化对带有圆形凹陷窝的小尺度矩形通道内湍流流动及对流换热的耦合影响.基于雷诺平均方法并结合SST k-ω湍流模型和煤油10组分替代模型,获得了不同深度圆形凹陷窝的旋涡结构及传热特性.计算结果表明,凹陷窝能够产生复杂的三维旋涡结构,明显改变了局部的湍流流动,从而导致壁面不同位置处的对流传热性能得到强化或者削弱.研究发现,随着凹陷窝深度的增加,壁面的平均努塞尔数先逐渐增大,当深度到达某一定值后,努塞尔数减小.根据流场的变化可知,当旋涡结构为马蹄涡和龙卷风涡时,带凹陷窝壁面的传热明显增强;而随着凹陷窝深度的进一步增加,旋涡结构变为非对称的羊角涡,导致传热性能下降.与努塞尔数的变化类似,摩擦因子同样随着凹陷窝深度的增加呈现先增大后减小的变化规律.