Abstract

The action of wave dominated flow on river bank leads to retreatment of the bankline thereby causing intense erosion issues. The understanding of the bank erosion process mechanisms is of great importance in the context of protecting or controlling the progressive growth of bankline which imposes a direct threat on near bank fertile agricultural land and habitats. The present study emphasizes on acquiring improved understanding on the bank erosion processes related to wave action that severely impact the bank erosion rate. Turbulent fluctuations of the near bank flow were observed to be modulated due to the interplay between eroded bank wall and stream flow under the influence of wave following and against the current. The fluctuating turbulent velocity field was measured using micro acoustic Doppler velocimeter (ADV) at regions close to the bank wall during the different stages of the erosion progress. Streamwise turbulence intensity was found to be relatively large upto a particular undercut depth during the erosion progression. The integral time and length scales and Taylor microscales were determined for different temporal stages using autocorrelation function. Results depict that wave current combined flow in conjunction with rough wall surface formed by the erosion process amplifies the turbulent kinetic energy and turbulent dissipation rate at vicinity of the wall. The velocity fluctuations show large intermittency as evaluated from Gaussian pdf for wave current combined flows. This may affect the near wall turbulence structures which is a causative factor for enhancement of erosion rate as compared to current only flow.

Article highlights

• Modulation of turbulence scales under wave current combined flow.

• Interaction between wave current combined flow and roughness formed in bank wall due to erosion.

• Turbulent structures and its effects on progressive bank erosion process.

中文翻译：

---

波流合流影响下渐进侵蚀边界湍流结构的时间调制

摘要

波浪主导的河流对河岸的作用导致河岸重新处理，从而导致严重的侵蚀问题。了解河岸侵蚀过程机制对于保护或控制河岸线的逐渐增长具有重要意义，河岸线对近岸肥沃的农田和栖息地造成直接威胁。本研究强调提高对与严重影响堤岸侵蚀率的波浪作用相关的堤岸侵蚀过程的理解。在波浪跟随和逆流的影响下，由于侵蚀的岸壁和溪流之间的相互作用，观察到近岸流的湍流波动受到调制。在侵蚀过程的不同阶段，使用微声多普勒测速仪（ADV）在靠近岸壁的区域测量了脉动湍流速度场。在侵蚀过程中，流向湍流强度被发现相对较大，直到特定的底切深度。使用自相关函数确定不同时间阶段的积分时间和长度尺度以及泰勒微尺度。结果表明，波流复合流与侵蚀过程形成的粗糙壁面相结合，放大了壁面附近的湍流动能和湍流耗散率。速度波动显示出大的间歇性，如从高斯 pdf 评估的波电流组合流动。

文章重点

• 波流合流下湍流尺度的调制。

• 波流合流与岸壁侵蚀形成的粗糙度之间的相互作用。

• 湍流结构及其对渐进式河岸侵蚀过程的影响。