Abstract Experiments and numerical simulations have been conducted to reveal the detailed turbulent flow and heat transfer characteristics over the surfaces with spherical dimples with different edge schemes, including the sharp edge, the fully rounded edge and the upstream rounded edge. The dimples have the same depth-to-diameter ratio of hd/d = 0.2. Steady-state heat transfer experiments were carried out for the turbulent flow over the three dimpled surfaces within the Reynolds number range of 10,000 ≤ ReDh ≤ 60,000, and the globally averaged heat transfer enhancements and friction factor ratios were obtained. Furthermore, transient liquid crystal thermography technique was used to obtain the local heat transfer characteristics on the dimpled surfaces. In addition, numerical simulations were carried out with a newly developed hybrid RANS-LES method of Stress-Blended Eddy Simulation (SBES) and the local heat transfer enhancement, detailed flow structure and turbulence statistics data were obtained and analyzed. The experimental results show that the best thermal performance is achieved by the dimples with upstream rounded edge, indicating an increase of about 11.4% in total heat transfer enhancement and an increase of about 5.2% in pressure loss when compared to the conventional dimples with sharp edge. The numerical results show that the flow over the dimpled surfaces can be divided into five zones: the mainstream zone, the recirculation zone, the Kelvin–Helmholtz vortex zone, the upwash zone and the rear separation zone, and each zone has its unique flow features. It is also found that the lowest pressure is achieved by the dimple with fully rounded edge, which is due to the absence of flow separation behind the rear edge of the dimple. The upstream-edge-rounded dimples show the reduced recirculation flow in the recirculation zone, the enhanced impingement and upwash flow in the upwash zone near the rear edge. These cause the stronger production of turbulent kinetic energy behind the rear edge, which are responsible for the higher thermal performance.

中文翻译：

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边缘圆形凹坑上湍流的实验和应力混合涡模拟

摘要 通过实验和数值模拟，揭示了具有不同边缘形式的球形凹坑表面的详细湍流和传热特性，包括锐边、全圆边和上游圆边。凹坑具有相同的深度直径比 hd/d = 0.2。对雷诺数10,000≤ReDh≤60,000范围内三个凹坑表面的湍流进行稳态传热实验，得到全局平均传热增强和摩擦系数比。此外，瞬态液晶热成像技术用于获得凹坑表面的局部传热特性。此外，数值模拟是使用新开发的混合 RANS-LES 应力混合涡模拟 (SBES) 方法进行的，并获得并分析了局部传热增强、详细的流动结构和湍流统计数据。实验结果表明，上游圆形边缘的凹坑实现了最佳的热性能，表明与传统锐边凹坑相比，总传热增强约11.4%，压力损失增加约5.2% . 数值结果表明，凹坑表面的流动可分为五个区：主流区、回流区、开尔文-亥姆霍兹涡区、上洗区和后分离区，每个区都有其独特的流动特征. 还发现最低压力是由具有完全圆形边缘的凹坑实现的，这是由于凹坑后边缘后面没有流动分离。上游边缘圆形的凹坑显示再循环区的再循环流减少，后边缘附近的上洗区中的冲击和上洗流增强。这些会导致后边缘后面产生更强的湍流动能，从而实现更高的热性能。