This study presents experimental investigations of entrainment events of a single sediment particle resting in a small pocket on a smooth bed in an open channel flow. The data were acquired with a tomographic particle tracking velocimetry system. The shake the box algorithm, a spatially high resolved Lagrangian tracking method, was applied to determine time-resolved and three-dimensional flow velocities in a volume during particle entrainment. The proper orthogonal decomposition (POD) method was applied to identify motions in the flow field carrying the most turbulent kinetic energy (TKE). Based on the POD method, the most energetic flow structures were linked with the occurring quadrant events at particle entrainment. It was shown that particle entrainment follows TKE peaks based on low-order POD modes caused by large sweeps. Two streamwise elongated counter rotating vortices with emerging sweeps in between were observed during particle entrainment. Here, most of the TKE exists in the first POD mode. This signature is suggested to be part of very large-scale coherent motions.

本研究介绍了在明渠流中光滑床上的小口袋中停留的单个沉积物颗粒的夹带事件的实验研究。使用断层扫描粒子跟踪测速系统获取数据。摇盒算法是一种空间高分辨率拉格朗日跟踪方法，用于确定粒子夹带过程中体积中的时间分辨和三维流速。应用适当的正交分解 (POD) 方法来识别携带最大湍动能 (TKE) 的流场中​​的运动。基于 POD 方法，最具活力的流动结构与粒子夹带时发生的象限事件相关联。结果表明，基于大扫描引起的低阶 POD 模式，粒子夹带遵循 TKE 峰值。在粒子夹带过程中观察到两个流向细长的反向旋转涡流，其间出现扫掠。在这里，大部分 TKE 存在于第一个 POD 模式中。这个签名被认为是非常大规模的相干运动的一部分。