The current paper investigates the flow and turbulence characteristics over dune bedforms by means of laboratory experiments, where spatially dense and temporally high frequency velocity measurements were done. Although similar studies are available in the literature, the focus and novelty of the current study is to assess the influence of surface roughness of the dune bedforms on the nearbed flow. For direct comparison, two different surface roughness heights over idealized, fixed-shaped, high-angled dune bedforms were tested; one with a hydraulically-smooth surface, and the other with a fully-rough surface. Spatial variation of time-averaged flow as well as turbulence statistics were examined, which was complemented by streamline plots and spectral analyses. The results are interpreted from sediment entrainment and sediment transport points of view. The results show that increased dune surface roughness reduces the nearbed flow velocity, but increases the flow velocities at upper regions. The upward directed flow near the dune crests becomes stronger in the case of smooth surface, while the re-attachment point moves further downstream compared to the rough wall case. It is concluded that the roughness of the dune surface affects the nearbed flow and turbulence characteristics qualitatively and quantitatively, which is shown to have direct consequences on sediment entrainment characteristics.

本论文通过实验室实验研究了沙丘床形的流动和湍流特性，在这些实验中进行了空间密集和时间上的高频速度测量。尽管文献中已有类似的研究，但是当前研究的重点和新颖性是评估沙丘床形的表面粗糙度对近床水流的影响。为了直接比较，测试了理想化，固定形状，高角度沙丘底座上两个不同的表面粗糙度高度；一个带有液压光滑的表面，另一个带有完全粗糙的表面。检验了时间平均流量的空间变化以及湍流统计数据，并辅以流线图和频谱分析。从泥沙夹带和泥沙输送的角度解释了结果。结果表明，增加的沙丘表面粗糙度会降低近床流速，但会增加上部区域的流速。在表面光滑的情况下，靠近沙丘波峰的向上流动会更强，而与粗糙壁面情况相比，重新连接点会向下游移动。得出的结论是，沙丘表面的粗糙度从质量和数量上都影响着近床层的流动和湍流特性，这直接影响了泥沙的夹带特性。在表面光滑的情况下，靠近沙丘波峰的向上流动会增强，而与粗糙壁面的情况相比，重新连接点会向下游移动。得出的结论是，沙丘表面的粗糙度从质量和数量上都影响着近床层的水流和湍流特性，这直接影响了泥沙的夹带特性。在表面光滑的情况下，靠近沙丘波峰的向上流动会增强，而与粗糙壁面的情况相比，重新连接点会向下游移动。得出的结论是，沙丘表面的粗糙度从质量和数量上都影响着近床层的水流和湍流特性，这直接影响了泥沙的夹带特性。