The role of energetic flow structures on the aeolian transport of sediment and plastic debris

Manousos Valyrakis, Xiao Zhao, Thomas Pähtz, Zhen Li
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Abstract

Recently, significant progress has been made in conceptually describing the dynamic aspects of coarse particle entrainment, which has been explored experimentally for open channel flows. The aim of this study is to extend the application of energy criterion to the low mobility aeolian transport of solids (including both natural sediment and anthropogenic debris such as plastics), ranging from incomplete (rocking) to full (rolling) entrainments. This is achieved by linking particle movements to energetic flow events, which are defined as flow structures with the ability to work on particles, setting them into motion. It is hypothesized that such events should impart sufficient energy to the particles, above a certain threshold value. The concept's validity is demonstrated experimentally, using a wind tunnel and laser distance sensor (LDS) to capture the dynamics of an individual target particle, exposed on a rough bed surface. Measurements are acquired at a high spatiotemporal resolution, and synchronously with the instantaneous air velocity at an appropriate distance upwind of the target particle, using a hot film anemometer. This enables the association of flow events with rocking and rolling entrainments. Furthermore, it is shown that rocking and rolling may have distinct energy thresholds. Estimates of the energy transfer efficiency, normalized by the drag coefficient, range over an order of magnitude (from about 0.001 to 0.0048 for rocking, up to about 0.01, for incipient rolling). The proposed event-based theoretical framework is a novel approach to characterizing the energy imparted from the wind to the soil surface and could have potential implications for modelling intermittent creep transport of coarse particles and related aeolian bedforms.
能流结构对沉积物和塑料碎片风化迁移的作用
最近,从概念上描述粗颗粒夹带动力学方面取得了重大进展,并对明渠水流进行了实验探索。本研究的目的是将能量标准的应用扩展到固体(包括天然沉积物和人为碎屑,如塑料)的低流动性风化输运,包括不完全(摇摆)到完全(滚动)夹带。要做到这一点,需要将颗粒运动与高能流事件联系起来,高能流事件被定义为能够作用于颗粒并使其运动的流动结构。根据假设,这种事件应该给粒子带来足够的能量,超过一定的临界值。实验证明了这一概念的有效性,使用风洞和激光测距仪(LDS)捕捉暴露在粗糙床面上的单个目标粒子的动态。测量采用高时空分辨率,并与目标颗粒上风向适当距离处的瞬时气流速度同步,使用的是热丝风速计。这样就能将流动事件与摇摆和滚动夹带联系起来。此外,研究还表明摇摆和滚动可能具有不同的能量阈值。所提出的基于事件的理论框架是描述风向土壤表面传递能量的一种新方法,可能对模拟粗颗粒间歇蠕动迁移和相关风化床形态具有潜在影响。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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