The present study examines the turbulent flow characteristics in the vicinity of the leading edge of a vertical retaining wall structure embedded in a gravel bed. Conditions before and during the initial stages of local scour development were considered. To that end, three laboratory experiments were carried out: one with fixed boundaries as a reference case, a second one with an erodible bed, but immobile channel bank, and a third one characterized by an erodible channel bed and bank. Instantaneous and time-averaged flow features, and turbulence statistics associated with the three-component velocity fields, obtained with a stereoscopic particle image velocimetry system, were analyzed. Water surface examination determined that channel bank erosion alters flow behavior upstream of the retaining wall. This change is manifested through more frequent formation of eddies near the top corner of the junction between the upstream face of the protrusion and the channel bank. Time-averaged and instantaneous velocity vector fields demonstrate the presence of two counter-rotating vortices in the experiments with the fixed channel bank, one located near the junction of retaining wall and the channel bed and one away from it generated as a result of a strong downflow. The latter motion represents a section of a horseshoe vortex. During the channel bank erosion, however, these vortices are not as significant and persistent. The results also indicate that the coherency and magnitude of the streamwise vorticity field diminish as a result of scour. However, it was confirmed that local turbulent kinetic energy and shear stresses increase in the presence of scour due to enhanced local flow separation.

中文翻译：

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砾石埋置式垂直挡土墙附近的流动动力学：与局部侵蚀初始阶段相对应的条件

本研究研究了埋在砾石层中的垂直挡土墙结构前缘附近的湍流特性。考虑了局部冲刷发展之前和初期的条件。为此，进行了三项实验室实验：一项以固定边界为参考案例，第二项具有可侵蚀的床但通道槽不固定，而第三项具有可侵蚀的通道床和槽。分析了通过立体粒子图像测速系统获得的瞬时和时间平均流动特征以及与三分量速度场相关的湍流统计数据。水面检查确定，河岸冲蚀改变了挡土墙上游的水流特性。这种变化通过在突起的上游面和通道堤之间的接合处的顶角附近更频繁地形成涡流来体现。时间平均和瞬时速度矢量场表明，在使用固定通道组的实验中，存在两个反向旋转的涡流，其中一个位于挡土墙与通道床的交汇点附近，而一个则由于强力波而产生。下流。后者代表马蹄涡旋的一部分。然而，在河岸侵蚀期间，这些涡旋并不那么显着且持久。结果还表明，由于冲刷，流向涡度场的相干性和大小减小。然而，