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首页> 外文期刊>International Journal of Heat and Fluid Flow >Turbulent rectangular ducts with minimum secondary flow
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Turbulent rectangular ducts with minimum secondary flow

机译：湍流矩形风管，次级流量最小

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摘要

In the present study we perform direct numerical simulations (DNSs) of fully-developed turbulent rectangular ducts with semi-cylindrical side-walls at Re-t,Re- c similar or equal to 180 with width-to-height ratios of 3 and 5. The friction Reynolds number Re-tau,Re- (c) is based on the centerplane friction velocity and the half-height of the duct. The results are compared with the corresponding duct cases with straight side-walls (Vinuesa et al., 2014), and also with spanwise-periodic channel and pipe flows. We focus on the influence of the semi-cylindrical side-walls on the mean cross-stream secondary flow and on further characterizing the mechanisms that produce it. The role of the secondary and primary Reynolds-shear stresses in the production of the secondary flow is analyzed by means of quadrant analysis and conditional averaging. Unexpectedly, the ducts with semi-cylindrical side-walls exhibit higher cross-flow rates and their secondary vortices relocate near the transition point between the straight and curved walls. This behavior is associated to the statistically preferential arrangement of sweeping events entering through the curved wall and ejections arising from the adjacent straight wall. Therefore, the configuration with minimum secondary flow corresponds to the duct with straight side-walls and sharp corners. Consequences on experimental facilities and comparisons between experiments and various numerical and theoretical models are discussed revealing the uniqueness of pipe flow.
机译：在本研究中，我们对完全开发的湍流矩形风管进行直接数值模拟（DNS），该矩形风管的Re-t，Re-c处的半圆柱侧壁近似或等于180，宽高比为3和5摩擦雷诺数Re-tau，Re-（c）基于中心平面的摩擦速度和管道的半高。将结果与相应的具有直侧壁的风管案例（Vinuesa等人，2014）以及跨展宽周期的通道和管道流进行了比较。我们关注半圆柱形侧壁对平均横流二次流的影响，并进一步描述产生它的机理。通过象限分析和条件平均分析了次级和主要雷诺剪切应力在次级流产生中的作用。出乎意料的是，具有半圆柱形侧壁的管道表现出更高的横流速率，并且其次级涡旋位于直壁和弯曲壁之间的过渡点附近。这种行为与通过弯曲壁进入的清扫事件和从相邻直壁产生的喷射的统计优先安排有关。因此，具有最小二次流量的配置对应于具有笔直侧壁和尖角的管道。讨论了实验设备的后果以及实验与各种数值和理论模型之间的比较，揭示了管道流动的独特性。

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