Abstract Large-eddy simulations are used to investigate flow structures and heat-transfer enhancements in rectangular channels with dimples and protrusions as Reynolds number varies from 5600 to 22,000. Roughness elements adopt sharp edges and are arranged inline, the ratios of their depths or heights to their respective print diameters are 0.1, and the ratio of channel height to dimple print diameter is 1.0. Comparisons are carried out between effects of Reynolds number and the gap between roughness elements, and the data presented include thermal performances, flow structures, local Nusselt numbers, local spatial correlation coefficients, characteristic frequencies, and turbulent kinetic energy. Results show that thermal performances can be increased considerably by either increasing Reynolds number or decreasing the gap ratio, but the type of flow structure is only related to Reynolds number. And inline arrangements for dimples and protrusions in many ways are equivalent to deepening the depth of the dimple, especially along the centerline of the arrangement, such that they can achieve higher thermal performances than a denser arrangement of dimples with a corresponding depth ratio. Meanwhile, sampling grids are deployed in the spacings between roughness elements to obtain local spatial correlation coefficients and characteristic frequencies. Frequent passing of vortical structures from roughness elements results in local minima of spatial correlation coefficients and protruding characteristic frequencies, and results show that contours of peak Nusselt numbers are in good correlation with them and thus directly resulting from these vortical structures and their enhancing effects. And it is found that the asymmetry in Nusselt number contours in the wake of the dimple is resulted from the combined influences of sizes of primary passages for vortical structures from dimples, shedding frequencies, and the turbulent kinetic energy carried by these vortical structures.

中文翻译：

---

使用大涡模拟研究具有凹坑和突起的矩形通道中的流动结构和传热增强

摘要 大涡模拟用于研究雷诺数从 5600 到 22,000 变化的带有凹坑和突起的矩形通道中的流动结构和传热增强。粗糙度元素采用锐利边缘并排成一行，其深度或高度与各自打印直径的比值为0.1，通道高度与凹坑打印直径的比值为1.0。比较了雷诺数的影响和粗糙度元素之间的差距，所呈现的数据包括热性能、流动结构、局部努塞尔数、局部空间相关系数、特征频率和湍流动能。结果表明，通过增加雷诺数或降低间隙比，可以显着提高热性能，但流动结构的类型只与雷诺数有关。并且凹坑和突起的内嵌排列在很多方面都相当于加深了凹坑的深度，尤其是沿着排列的中心线，这样它们比具有相应深度比的更密集的凹坑排列可以获得更高的热性能。同时，在粗糙度元素之间的间距中部署采样网格，以获得局部空间相关系数和特征频率。来自粗糙度元素的涡旋结构的频繁通过导致空间相关系数和突出特征频率的局部最小值，结果表明，峰值努塞尔数的等值线与它们具有良好的相关性，因此直接由这些涡旋结构及其增强效应产生。并发现凹坑尾迹的努塞尔数等高线的不对称性是由凹坑涡结构的主要通道尺寸、脱落频率和这些涡结构携带的湍流动能共同影响的结果。