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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Detection and reconstruction of large-scale coherent flow structures in gravel-bed rivers
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Detection and reconstruction of large-scale coherent flow structures in gravel-bed rivers

机译：砾石河道大型相干流结构的检测与重建

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摘要

Large-scale flow structures (LSFS) in the streamwise direction are important features of gravel-bed river flows, because they may contribute to sediment transport and gas exchange. In the present study, these structures are detected using Huang's empirical mode decomposition and reconstructed with phase-averaging techniques based on a Hilbert transform of the velocity signal. The analysis is based on the fluctuating component of 15 quasi-instantaneous velocity profiles measured with a three-dimensional (3D) acoustic Doppler velocity profiler (ADVP) in an armoured gravel-bed river with a low relative submergence of 2.9 (ratio between flow depth and bed grain diameter). LSFS were identified in most of the measured profiles and consistently showed similar features. We were able to characterize the geometry of these large-scale coherent structures: the front has a vertical linear shift in the time domain and a vertical profile corresponding to a first quarter moon with the apex situated at z/h approximate to 0.4. In the vertical, the front scales with flow depth h, and in the streamwise direction, LSFS scale with three to seven times the mean flow depth. On the bed, the effect of LSFS is a periodic non-linear variation of the friction velocity on average between 0.90 and 1.10 times the mean value. A model for the friction velocity cycle resulting from LSFS oscillation is presented. Copyright (c) 2014 John Wiley & Sons, Ltd.
机译：沿河道的大型水流结构（LSFS）是砾石河床水流的重要特征，因为它们可能有助于泥沙输送和气体交换。在本研究中，这些结构使用Huang的经验模式分解进行检测，并使用基于速度信号的希尔伯特变换的相位平均技术进行重构。该分析基于使用三维（3D）声多普勒速度剖面仪（ADVP）在装甲砾石床河中测得的15个准瞬时速度剖面的波动分量进行分析，相对下沉度为2.9（流量深度之间的比率）和床身直径）。 LSFS在大多数测得的曲线中均被识别，并始终显示出相似的特征。我们能够表征这些大型相干结构的几何形状：正面在时域中具有垂直线性位移，并且其垂直轮廓对应于第一个四分之一月，其顶点位于z / h处大约为0.4。在垂直方向，前部标尺的深度为流动深度h;在垂直方向上，LSFS标尺的平均深度为三至七倍。在床上，LSFS的影响是摩擦速度的周期性非线性变化，平均值在平均值的0.90到1.10倍之间。提出了由LSFS振荡产生的摩擦速度循环的模型。版权所有（c）2014 John Wiley＆Sons，Ltd.

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