Abstract

This work performs a direct simulation on forced convection heat transfer of flow past a square cylinder in a channel with an upstream promoter. The promoter is small in size that the incoming flow is stagnated and heated, thus the flow in the gap between the promoter and main cylinder keeps steady and the heating by the main cylinder gets weak as it develops downstream. The objective of the present study is to explore the effects of two parameters, i.e., Reynolds number and gap ratio, on the thermal and flow characteristics for Re = 70-140 and GR = 2-8. The effects of the two parameters are presented and analyzed by the thermal and flow fields, variations of global characteristics quantities, local heat transfer characteristics, patterns of flow in the gap and near-wake region, and temperature on the channel walls. We emphasize both time-averaged and fluctuating quantities to reflect the mean and pulsating characteristics of the flow. Numerical results reveal that although the promoter produces a steady flow in the gap, it alters the velocity profile of the gap flow and consequently changes the shearing properties, thus influences the flow around and even in the wake downstream of the main cylinder. In general, the small promoter partially stabilizes the wake flow and reduces the amplitude of fluctuating forces acting on the main cylinder compared with the single cylinder configuration, and the stabilization is more remarkable for small gap ratios. However, the fluctuation of heat transfer rate on the surface of main cylinder may increase. A further analysis indicates that as the promoter is placed close to the main cylinder, the recovery rate of deficit wake flow is slower and the fluctuating amplitude of velocity and temperature is relatively smaller due to the stabilized flow.

摘要

这项工作对流过带有上游助推器的通道中的方形圆柱体的强制对流热传递进行了直接模拟。助推器体积小，进料流滞流受热，助推器与主缸间隙内流动稳定，主缸加热向下游减弱。本研究的目的是探索两个参数，即雷诺数和间隙比，对Re  = 70-140 和GR的热和流动特性的影响 = 2-8。通过热场和流场、全局特征量的变化、局部传热特征、间隙和近尾流区域的流动模式以及通道壁上的温度来呈现和分析这两个参数的影响。我们强调时间平均和波动量来反映流动的平均和脉动特性。数值结果表明，虽然促进剂在间隙中产生稳定的流动，但它改变了间隙流动的速度剖面，从而改变了剪切特性，从而影响了主圆柱体周围甚至尾流下游的流动。一般来说，与单缸配置相比，小启动子部分地稳定了尾流并降低了作用在主缸上的波动力的幅度，小间隙比的稳定性更显着。然而，主缸表面传热率的波动可能会增加。进一步分析表明，由于助推器靠近主缸放置，由于流动稳定，逆流的恢复速度较慢，速度和温度的波动幅度相对较小。