Force and torque acting on particles in a transitionally rough open-channel flow
Force and torque acting on particles in a transitionally rough open-channel flow
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DOI：
10.1017/jfm.2011.311
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发表时间：
2011-08
影响因子：
3.7
通讯作者：
Clemens Chan-Braun;Manuel Garc'ia-Villalba;M. Uhlmann
中科院分区：
文献类型：
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作者：
Clemens Chan-Braun;Manuel Garc'ia-Villalba;M. Uhlmann
本文对明渠绕几何粗糙壁流动进行了直接数值模拟，总雷诺数为${\mathit{Re}}_{B} \约2900$。这堵墙由一层正方形排列的球体组成。审议了两个案例。在第一种情况下，球体很小（直径相当于10美元）。7$壁单元）和水力光滑流态的极限接近。在第二种情况下，球体大三倍以上（49美元）。3$壁面单元），流动处于过渡粗糙流态。特别强调的是由于湍流的力和扭矩作用在颗粒上的特性。结果发现，在这两种情况下，平均阻力，升力和展向扭矩在很大程度上产生在颗粒表面的顶部区域。粒子力波动的强度在大球体的情况下显着较大，而趋势不同的扭矩的各个分量的波动。一个简化的模型被用来表明，转矩波动可能被解释为作为一个过滤器的流量尺度的大小，可以有效地产生转矩波动的球体。波动的力和扭矩被发现表现出强烈的非高斯概率密度函数，特别是长尾，这是更明显的小球体的情况下的效果。一些影响，目前的研究结果泥沙侵蚀进行了简要讨论。
Abstract Direct numerical simulation of open channel flow over a geometrically rough wall has been performed at a bulk Reynolds number of ${\mathit{Re}}_{b} \approx 2900$. The wall consisted of a layer of spheres in a square arrangement. Two cases have been considered. In the first case the spheres are small (with diameter equivalent to $10. 7$ wall units) and the limit of the hydraulically smooth flow regime is approached. In the second case the spheres are more than three times larger ($49. 3$ wall units) and the flow is in the transitionally rough flow regime. Special emphasis is given to the characterisation of the force and torque acting on a particle due to the turbulent flow. It is found that in both cases the mean drag, lift and spanwise torque are to a large extent produced at the top region of the particle surface. The intensity of the particle force fluctuations is significantly larger in the large-sphere case, while the trend differs for the fluctuations of the individual components of the torque. A simplified model is used to show that the torque fluctuations might be explained by the spheres acting as a filter with respect to the size of the flow scales which can effectively generate torque fluctuations. Fluctuations of both force and torque are found to exhibit strongly non-Gaussian probability density functions with particularly long tails, an effect which is more pronounced in the small-sphere case. Some implications of the present results for sediment erosion are briefly discussed.