Oscillatory boundary layer over fixed rough beds
Oscillatory boundary layer over fixed rough beds
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发表时间：
1982
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通讯作者：
S. Borghei
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作者：
S. Borghei
由于对沿海环境中结构工程设计的需求日益增长，对重力波作用下的水流特性的精确研究已成为首要任务。虽然已经进行了许多研究，但由于缺乏足够的速度测量仪器，基础研究进展缓慢。然而，近年来，激光多普勒测速仪的发展使得有可能在不干扰流动的情况下观察非常接近床的轨道速度。在这项研究中使用了这种技术，在重力波下的振荡流的观察进行了以上光滑，二维和三维粗糙床。对于光滑的床的情况下，它被发现，整个深度的速度分布很好地提出了斯托克斯二阶剪切波方程，除了理论预测低估了观测结果，并获得了线性关系的速度系数之间的两组值。至于平均速度的配置文件是在密切的协议与Longuet-Higgins的传导解决方案，它被发现有一个负值（在相反的方向波的进展）在大部分的流体和总是正值内的边界层。粗糙床对大部分流体的流动几乎没有影响。对于边界层内部，由于粗糙床的尺寸较大，层流边界层被消除，但对于小尺寸的粗糙床，在边界层边缘处流动变为层流，并且可以追踪到扰动的层流边界层速度分布。然而，两个粗糙床有相似的影响，除了粗糙度的大小和雷诺数的值。在粗糙床的粗糙度元素内，清楚地观察到涡流的形成，并对这些形成的测量的综合范围进行了分析和讨论。
The accurate study of characteristics of the flow under gravity waves has become of prime importance due to the growing demand for structural engineering designs in the coastal environment. Although many investigations have been carried out, the progress of fundamental research was slow due to the lack of an adequate velocity measuring instrument. However in recent years, the development of the Laser Doppler Velocimeter has made it possible to observe the orbital velocity very close to a bed without disturbing the flow. This technique was used in this investigation, in which observations of the oscillatory flow under gravity waves were carried out above smooth, two-dimensional and three-dimensional rough beds. For the smooth bed case it was found that the velocity profile throughout the depth was well presented by the Stokes second order shear wave equation, except that the theoretical predictions underestimated the observed results, and a linear relationship was obtained for the velocity coefficients between the two sets of values. As for mean velocity the profile was in close agreement with the Longuet- Higgins conduction solution, and it was found to have a negative value (in opposite direction to wave progression) in the bulk of fluid and always positive values within the boundary layer. The rough beds made little change to the flow in the bulk of fluid. As for inside the boundary layer, the laminar boundary layer was eliminated due to the large size of the rough bed, but for a small size rough bed the flow became laminar at the edge of the boundary layer, and a perturbed laminar boundary layer velocity profile was traceable. However, the two rough beds had similar influences on the flow except for the roughness size and Reynolds number values. Inside the roughness elements of the rough beds vortex formation was clearly observed and the comprehensive range of measurements of these formations are analysed and discussed.