Direct bed shear stress measurements in bore-driven swash
Direct bed shear stress measurements in bore-driven swash
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DOI：
10.1016/j.coastaleng.2009.04.004
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发表时间：
2009-08-01
影响因子：
4.4
通讯作者：
Baldock, T. E.
中科院分区：
文献类型：
--
作者：
Barnes, M. P.;O'Donoghue, T.;Baldock, T. E.
直接测量床剪切冲带。这些数据是在中型和大型实验室钻孔驱动的冲流中使用剪切板获得的，并涵盖了宽范围的床面粗糙度。在整个冲浪区宽度上获得数据，并与内碎波区的数据进行对比。通过数值模拟和校准对测量的速度数据，获得了通过整个旋转斜流循环的流速估计。测量的应力和计算的流速随后被用来反计算瞬时局部表面摩擦系数，使用二次阻力定律。数据显示，通过上涌前缘的床面剪切应力随时间迅速变化，通常比相应流速下的上涌剪切应力大2 - 4倍。测量结果表明，强烈的时间变化的表面摩擦系数，特别是在摩擦系数。表面摩擦系数与雷诺数的一般行为是符合经典理论的某些阶段的冲洗循环。表面摩擦系数的空间变化也被确定，这是最大的冲浪冲边界，并可能与当地湍流强度的变化。上涌过程中的表面摩擦系数约为相应雷诺数和跨岸位置处的上涌过程中的表面摩擦系数的两倍。有人建议，这是一个结果的无滑移条件在尖端导致一个不断发展的前缘和边界层，其中高速流体和动量不断注入从后面和上方的尖端区域的流动。最后，实测应力数据被用来确定的不对称性和跨海岸变化的潜在输沙预测的三种形式的输沙公式。皇冠版权所有（C）2009年出版的爱思唯尔B. V.保留所有权利。
Direct measurements of bed shear in the swash zone are presented. The data were obtained using a shear plate in medium and large-scale laboratory bore-driven swash and cover a wide range of bed roughness. Data were obtained across the full width of the swash zone and are contrasted with data from the inner surf zone. Estimates of the flow velocities through the full swash cycle were obtained through numerical modelling and calibrated against measured velocity data. The measured stresses and calculated flow velocities were subsequently used to back-calculate instantaneous local skin friction coefficients using the quadratic drag law. The data show rapid temporal variation of the bed shear stress through the leading edge of the uprush, which is typically two-four times greater than the backwash shear stresses at corresponding flow velocity. The measurements indicate strong temporal variation in the skin friction coefficient, particularly in the backwash. The general behaviour of the skin friction coefficient with Reynolds number is consistent with classical theory for certain stages of the swash cycle. A spatial variation in skin friction coefficient is also identified, which is greatest across the surf-swash boundary and likely related to variations in local turbulent intensities. Skin friction coefficients during the uprush are approximately twice those in the backwash at corresponding Reynolds number and cross-shore location. It is suggested that this is a result of the no-slip condition at the tip leading to a continually developing leading edge and boundary layer, into which high velocity fluid and momentum are constantly injected from the flow behind and above the tip region. Finally, the measured stress data are used to determine the asymmetry and cross-shore variation in potential sediment transport predicted by three forms of sediment transport formulae. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.