Direct numerical simulation of horizontal open channel flow with finite-size, heavy particles at low solid volume fraction
Direct numerical simulation of horizontal open channel flow with finite-size, heavy particles at low solid volume fraction
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DOI：
10.1088/1367-2630/15/2/025031
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发表时间：
2013-01
影响因子：
3.3
通讯作者：
Aman G. Kidanemariam;Clemens Chan-Braun;Todor Doychev;M. Uhlmann
中科院分区：
文献类型：
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作者：
Aman G. Kidanemariam;Clemens Chan-Braun;Todor Doychev;M. Uhlmann
我们对光滑水平壁面上有限尺寸重颗粒存在时的明渠湍流流动进行了直接的数值模拟。球形颗粒的直径约为7壁单位，密度为流体密度的1.7倍，固体体积分数为5×10−4。伽利略数的值设置为16.5，而屏蔽参数约为0.2。在这些条件下，颗粒主要分布在底壁附近，在那里它们表现出强烈的择优浓度，我们通过Voronoi分析和计算颗粒条件浓度场来定量。在以前的类似参数值的研究中观察到，颗粒的平均流向速度比流体的速度小。我们提出了一个新的定义，由有限大小的颗粒‘看到’的流体速度的基础上平均在一个球面分段，由此我们推断，在目前的情况下，颗粒瞬时落后于流体只有很小的量。颗粒条件下的流体速度场表明，颗粒优先驻留在低速条纹中，导致观察到的表观滞后。最后，涡排出研究表明，粒子沿展宽方向的运动与位于近壁粒子附近的具有相应旋转感的涡旋的存在显著相关。
We have performed direct numerical simulation of turbulent open channel flow over a smooth horizontal wall in the presence of finite-size, heavy particles. The spherical particles have a diameter of approximately 7 wall units, a density of 1.7 times the fluid density and a solid volume fraction of 5 × 10−4. The value of the Galileo number is set to 16.5, while the Shields parameter measures approximately 0.2. Under these conditions, the particles are predominantly located in the vicinity of the bottom wall, where they exhibit strong preferential concentration which we quantify by means of Voronoi analysis and by computing the particle-conditioned concentration field. As observed in previous studies with similar parameter values, the mean streamwise particle velocity is smaller than that of the fluid. We propose a new definition of the fluid velocity ‘seen’ by finite-size particles based on an average over a spherical surface segment, from which we deduce in the present case that the particles are instantaneously lagging the fluid only by a small amount. The particle-conditioned fluid velocity field shows that the particles preferentially reside in the low-speed streaks, leading to the observed apparent lag. Finally, a vortex eduction study reveals that spanwise particle motion is significantly correlated with the presence of vortices with the corresponding sense of rotation which are located in the immediate vicinity of the near-wall particles.