双向耦合如何修改多尺度优先扫描机制
How two-way coupling modifies the multiscale preferential sweeping mechanism
摘要：
对于单向耦合（1 WC）流，Tom & Bragg（J. Fluid Mech.，871，pp. 244-270，2019）推进了Maxey的分析（J. Fluid Mech.，174，pp. 441-465，1987），其适用于弱惯性颗粒，适用于任意惯性的颗粒，并且新的理论结果揭示了不同尺度在导致湍流中增强的颗粒沉降的优先清扫机制中所起的作用。蒙绍-德琼（Phys. Rev. Fluids，2，104302，2017）使用直接数值模拟（DNS）表明，虽然对于低颗粒负载，双向耦合（2 WC）对全局流动统计的影响很弱，但2 WC使颗粒能够将其附近的流体拖下，从而显著增强其沉降，他们认为2 WC抑制了优先扫描机制。我们进一步探讨这一点，考虑2 WC的影响，由不同大小的涡流对颗粒沉降的贡献。与Monchaux和Dejoan的协议，我们表明，即使在低负荷，2 WC强烈增强颗粒沉降，我们展示了2 WC如何修改不同的流量尺度的贡献。然而，与他们的研究相反，我们发现，优惠清扫仍然是重要的2 WC流量。特别地，对于1 WC和2 WC流，由于湍流引起的沉降增强由来自流的应变区域中的颗粒的贡献主导，但是对于2 WC情况，这些区域中的颗粒还将流体与它们一起向下拖曳，导致与1 WC情况相比它们的沉降增强。
英文摘要：
For one-way coupled (1WC) flows, Tom & Bragg (J. Fluid Mech., 871, pp. 244-270, 2019) advanced the analysis of Maxey (J. Fluid Mech., 174, pp. 441-465, 1987), which applied to weakly inertial particles, to particles of arbitrary inertia, and the new theoretical result revealed the role that different scales play in the preferential sweeping mechanism that leads to enhanced particle settling in turbulent flows. Monchaux & Dejoan (Phys. Rev. Fluids, 2, 104302, 2017) showed using direct numerical simulations (DNS) that while for low particle loading the effect of two-way coupling (2WC) on the global flow statistics is weak, 2WC enables the particles to drag the fluid in their vicinity down with them, significantly enhancing their settling, and they argued that 2WC suppresses the preferential sweeping mechanism. We explore this further by considering the impact of 2WC on the contribution made by eddies of different sizes on the particle settling. In agreement with Monchaux & Dejoan, we show that even for low loading, 2WC strongly enhances particle settling, and we show how 2WC modifies the contribution from different flow scales. However, contrary to their study, we show that preferential sweeping remains important in 2WC flows. In particular, for both 1WC and 2WC flows, the settling enhancement due to turbulence is dominated by contributions from particles in straining regions of the flow, but for the 2WC case, the particles in these regions also drag the fluid down with them, leading to an enhancement of their settling compared to the 1WC case.
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