[论文解读] Investigating the mechanism by which finite-size heavy particles are entrained in turbulent open channel flow over a smooth surface

Tatia Bzikadze, Markus Weyrauch+1 more|arXiv (Cornell University)|Jan 27, 2026

Particle Dynamics in Fluid Flows被引用 0

一句话总结

论文使用粒子分辨DNS分析有限尺寸重颗粒在光滑壁面的湍流开放通道流中的夹带，并在自由运动、旋转受限和跨向运动受限的情形间进行比较，以识别升力驱动的夹带机制以及相干结构的作用。

ABSTRACT

The dynamics of entrainment of finite-size heavy particles in a turbulent open channel flow over a smooth surface are analyzed. Three types of simulations, namely with freely moving, rotation-constrained, and spanwise-motion-constrained particles, were conducted using particle-resolved direct numerical simulations. With the aid of a relative velocity suitably defined in the vicinity of the finite-size particle, we decompose the hydrodynamic force into drag and lift contributions and evaluate the local wall-normal shear rate around the particles. By means of coherent structure eduction techniques, we investigate flow structures before and during lift-off events. Rotation-constrained simulations revealed the insignificance of particle rotation in the entrainment mechanism. Spanwise-motion-constrained simulations revealed the importance of particle location with respect to flow structures with apparent changes in entrainment frequency, duration of the entrainment process, wall-normal shear around the particles, and distance to the nearest vortical structures during lift-off. The contribution of lift to the wall-normal force is found to be responsible for the initiation of particle entrainment, which is induced by a high-shear event associated with fast-moving fluid. The presence of quasi-streamwise vortices is shown to be an important ingredient for the entrainment of particles into the bulk flow. The results show that, at marginal Shields number values, a high wall-normal shear rate and the proximity of an intense quasi-streamwise vortex are essential elements of the entrainment mechanism.

研究动机与目标

• 阐明在光滑壁面的湍流开放通道流中，有限尺寸重颗粒起始抬离的机制。
• 量化在夹带过程中阻力和升力对水动力力的相对贡献。
• 评估粒子转动和跨向运动对升离与流场结构取样的影响。
• 研究近壁相干结构，特别是准流向涡旋，在粒子夹带中的作用。

提出的方法

• 用浸没边界法求解不可压Navier–Stokes方程以模拟自由移动的颗粒。
• 用牛顿-欧拉方程表示颗粒运动，包含流体力、接触力和重力。
• 利用在颗粒周围定义的相对速度，将水动力力分解为阻力和升力。
• 对旋转或跨向运动进行约束，以评估它们对夹带的影响。
• 通过基于阈值的壁法向位移检测来识别抬离事件，并分析相关的流场结构。

实验结果

研究问题

• RQ1 在湍流开放通道流中，哪些机制会使重型有限尺寸颗粒从底壁抬离？
• RQ2 在抬离过程中，阻力和升力对水动力力的贡献如何随局部流场特征变化？
• RQ3 与旋转受限情形相比，颗粒转动是否影响夹带？
• RQ4 约束跨向运动是否改变抬离频率以及与相干结构的相互作用？

主要发现

• 升力是引发夹带的主要贡献者，其壁法向力超过颗粒重量。
• 跨向运动受限会增加夹带频率，表明对更广泛流场结构的采样影响升离。
• 在所研究条件下，粒子转动对夹带的影响可以忽略。
• 近壁准流向涡旋和高壁法向剪切对边界处的升离至关重要，且在边界层数值接近临界的情况尤为明显。
• 夹带事件与高剪切事件以及接近强烈准流向涡旋相关。
• 研究结果确认升力（由临近流体的局部高剪切流驱动）是再悬浮的关键机制。