Flow structure and heat transfer of a sweeping jet impinging on a flat wall
Flow structure and heat transfer of a sweeping jet impinging on a flat wall
复制标题
DOI：
10.1016/j.ijheatmasstransfer.2018.04.016
复制
发表时间：
2018-09
影响因子：
5.2
通讯作者：
Tongil Park;Kursat Kara;Daegyoum Kim
中科院分区：
文献类型：
--
作者：
Tongil Park;Kursat Kara;Daegyoum Kim
冲击射流由于其显著的对流换热性能而得到了广泛的研究，而周期振荡的扫掠射流的冲击却很少引起人们的兴趣。我们实验研究了几个雷诺数和挡板间距的扫掠射流冲击平壁的传热，并发现了非定常流动结构来表征传热能力。局部努塞尔数的壁面上进行了评估，通过测量温度与热电偶，并使用粒子图像测速仪定量可视化的流动。Nusselt数的分布不同于圆形射流，呈现出两个不同的区域。在扫掠射流的中心附近，形成高努塞尔数区，而没有在圆形射流中通常观察到的明显峰值。远离中心区域，努塞尔数单调减小。在这两个区域的努塞尔数的趋势相关的第一模式的流动结构得到适当的正交分解（POD）。这两个区域的边界是第一POD模在近壁处的一个局部极小值，在高Nusselt数的中心区域，第一POD模的幅值较大。研究还发现，两个区域的平均横向速度和横向速度脉动的分布有明显的差异，这意味着在分析换热性能时应同时考虑这两个量。
While an impinging jet has been widely investigated because of its remarkable convective heat transfer performance, the impingement of a sweeping jet which undergoes periodic oscillation has drawn little interest. We experimentally examined the heat transfer of a sweeping jet impinging on a flat wall for several Reynolds number and nozzle-to-plate spacings and discovered unsteady flow structure to characterize heat transfer capability. Local Nusselt number on the wall was evaluated by measuring temperature with thermocouples, and a flow was visualized quantitatively using particle image velocimetry. The distribution of the Nusselt number is different from that of a round jet, exhibiting two distinct regions. Near the center of a sweeping jet, a high Nusselt number zone is formed without a noticeable peak commonly observed in a round jet. Away from the central region, the Nusselt number decreases monotonically. The trends of the Nusselt number at the two regions are correlated with the first mode of the flow structure obtained by proper orthogonal decomposition (POD). The boundary of the two regions is a local minimum of the first POD mode near the wall, and the magnitude of the first POD mode is large in the central region of high Nusselt number. It was also found that the distributions of mean lateral velocity and lateral velocity fluctuation were clearly different between the two regions, which implies that both quantities should be considered for the analysis of heat transfer performance.