Flow separation and roughness lengths over large bedforms in a tidal environment

This study characterises the shape of the flow separation zone (FSZ) and wake region over large asymmetric bedforms under tidal flow conditions. High resolution bathymetry, flow velocity and turbulence data were measured along two parallel transects in a tidal channel covered with bedforms. The field data are used to verify the applicability of a numerical model for a systematic study using the Delft3D modelling system and test the model sensitivity to roughness length. Three experiments are then conducted to investigate how the FSZ size and wake extent vary depending on tidally-varying flow conditions, water levels and bathymetry. During the ebb, a large FSZ occurs over the steep lee side of each bedform. During the flood, no flow separation develops over the bedforms having a flat crest; however, a small FSZ is observed over the steepest part of the crest of some bedforms, where the slope is locally up to 15°. […]

本研究对潮汐流动条件下大型非对称床形流分离区（FSZ）和尾流区域的形状进行了表征。在覆盖有床形的潮汐通道中，沿两条平行横断面测量了高分辨率地形、流速和湍流数据。这些实地数据被用于验证Delft3D模拟系统在系统研究中的应用性，并测试模型对粗糙度的敏感性。随后进行了三项实验，以探究FSZ大小和尾流范围如何随潮汐变化的流速、水位和地形而变化。在落潮期间，每个床形的下游陡峭侧面都会出现一个大的FSZ。在涨潮期间，平坦顶部的床形上不会发展出流分离；然而，在部分床形的顶部最陡峭的部分，观察到小的FSZ，其局部坡度高达15°。...