Direct numerical simulations two-way coupled with inertial particles are used to investigate the particle distribution and two-way coupling mechanisms in turbulent open channel flow. In particular, the relationship between low- and high-inertia particles and the distinct large-scale motions (LSMs) and very-large-scale motions (VLSMs) which are characteristic of high-Reynolds number, wall-bounded turbulence are examined. To do this, two methods of spatial filtering are applied, to isolate the effects of LSMs versus VLSMs and separately analyze their interactions with inertial particles}. One method of filtering the VLSMs from the flow is via artificial domain truncation, which alters the mean particle concentration profile and particle clustering due to the absence of VLSMs. The second method uses on-the-fly} low- and high-pass filtering on the velocity field seen by the particles, so that as the simulation progresses the} particles can only couple with certain scales of the flow. The results show that turbophoretic drift of particles towards the wall and the resulting increase in near-wall concentration} is under-predicted without VLSMs, whereas the small-scale clustering} and two-way coupling effects are mainly determined by particle coupling with LSMs. In the inner layer, the elongated streamwise anisotropic particle clustering can be reproduced by coupling solely with LSMs for low Stokes number. However, we do not observe a similar particle clustering behavior in the outer layer as seen in the full simulation by coupling particles with either LSMs or VLSMs at high Stokes numbers. This indicates that the organized particle structures are formed by the joint action of LSMs and VLSMs, especially for high Stokes number particles in the outer layer. The implications of these scale interactions are discussed in the context of LES of one- and two-way coupled flows.

中文翻译：

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明渠流中惯性粒子与湍流的多尺度相互作用

直接数值模拟双向耦合惯性粒子用于研究湍流明渠流动中的粒子分布和双向耦合机制。特别地，检查了低惯性和高惯性粒子与高雷诺数，壁边界湍流所特有的独特的大规模运动（LSM）和超大规模运动（VLSM）之间的关系。为此，应用了两种空间滤波方法，以隔离LSM与VLSM的影响，并分别分析其与惯性粒子的相互作用}。从流中过滤VLSM的一种方法是通过人工域截断，由于不存在VLSM，它会改变平均颗粒浓度分布和颗粒聚类。第二种方法是对粒子所看到的速度场进行动态的低通和高通滤波，因此随着模拟的进行，粒子只能与一定比例的流动耦合。结果表明，在没有VLSM的情况下，颗粒向壁的涡轮漂移和由此引起的近壁浓度的增加是低估的，而小规模的聚集和双向耦合效应则主要由与LSM的颗粒耦合决定。在内层中，可以通过仅与低斯托克斯数的LSM耦合来复制细长的流向各向异性粒子簇。但是，我们没有观察到通过将粒子与高Stokes数的LSM或VLSM耦合而在整个模拟中看到的外层相似的粒子聚集行为。这表明，有组织的粒子结构是由LSM和VLSM的共同作用形成的，特别是对于外层中高斯托克斯数的粒子。这些规模相互作用的含义在单向和双向耦合流动的LES的背景下进行了讨论。