The present study experimentally investigated near-bed coherent structures of turbulence over rough surface in the presence of surface waves over the steady current by replicating it in a laboratory flume. The rough surface was modelled by using wooden ribs of square cross section extended across the whole channel width of flume. The instantaneous velocities at different positions in the flow field were measured by using an acoustic Doppler velocimeter. The recorded velocities data were examined to investigate the coherent structures of turbulence near rough surface using the spatio-temporal averaging approach. Pre-multiplied velocity spectra, co-spectral, and coherency were evaluated in frequency domain at different vertical positions under different flow conditions. Length scales were determined to quantify the eddy size within the flow domain, and the anisotropy invariant maps were also obtained to characterize the anisotropic flow under different roughness conditions in wave-current flow cases. Results show increased correlation between velocity fluctuations in the large-scale low-frequency region due to the addition of surface waves, which accounts for the major part of Reynolds stress. Furthermore, turbulence dissipation in the near-bed region was found to be strongly dependent on roughness characteristics.

本研究通过在实验室水槽中进行复制，实验性地研究了在稳定电流上存在表面波的情况下，在粗糙表面上湍流附近的近床相干结构​​。粗糙的表面是通过使用在水槽的整个通道宽度上延伸的方形横截面的木肋来建模的。通过使用声学多普勒测速仪测量流场中不同位置的瞬时速度。使用时空平均方法检查记录的速度数据，以研究粗糙表面附近湍流的相干结构。在不同流动条件下不同垂直位置的频域中，对预乘速度谱，共谱和相干性进行了评估。确定长度刻度以量化流域内的涡流大小，并获得各向异性不变图来表征波流情况下不同粗糙度条件下的各向异性流动。结果表明，由于增加了表面波，大型低频区域的速度波动之间的相关性增加，这是雷诺应力的主要部分。此外，发现在近床区的湍流消散强烈依赖于粗糙度特性。