Abstract

Sediment mobility in stream corroborates many significant mechanisms in terms of interactions of transported particles in the carrier fluid flows. In general, the sediment entrainment in stream refers to temporal and continual motion of non-cohesive grains. This phenomenon significantly influences the near-bed turbulent flow characteristics in streams. Laboratory experiments were conducted in a rectangular open-channel flume of 15 m long, 0.90 m wide and 0.75 m deep fitted with side glass walls and the study is concerned with the determination of von Kármán coefficient with non-cohesive bed-load to strive the eddy traversing length, sizes and TKE dissipation rate close to the bed. Two modes of experimental conditions are considered: (1) immobile-bed with no sediment transport known as clear-water flows; and (2) continuous weak bed-load sediment transport, without bed-forms development refer to a mobile-bed flows. In both cases, the sediment beds should remain flat and hydraulically rough. The experimental result reveals that the von Kármán coefficient goes down in the traditional log-law of wall in mobile-bed streams with respect to the flow over an immobile bed. A close observation in sediment mobility due to bed load transport shows the reduction in traversing length of an eddy and increment in near-bed eddy size. The increment in near-bed eddy sizes are attributed to the reduction in turbulent kinetic energy dissipation rate close to the stream bed.

中文翻译：

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沉积物迁移率对河流中通用vonKármán系数k和涡流遍历长度的影响

摘要

就输送流体在载流中的相互作用而言，河流中的泥沙迁移率证实了许多重要的机制。通常，流中夹带的泥沙是指非粘性颗粒的时间和连续运动。这种现象显着影响流中近床湍流的特性。在长15 m，宽0.90 m，深0.75 m并装有侧玻璃墙的矩形明渠水槽中进行了实验室实验，该研究与非粘性床荷的vonKármán系数的确定有关，以努力涡流的移动长度，尺寸和TKE耗散率都接近床身。考虑了两种模式的实验条件：（1）固定床，没有沉积物传输，称为清水流；（2）连续的弱床底泥沙输送，没有形成床形，是指流动床流。在这两种情况下，沉积物床都应保持平坦和液压粗糙。实验结果表明，相对于固定床的流量，传统的移动床流墙壁对数律中的vonKármán系数下降。密切观察由于床层负荷输送所引​​起的泥沙迁移率，表明涡流的穿越长度减少，近床层涡流尺寸增加。近床涡流尺寸的增加归因于靠近流床的湍动能耗散率的降低。