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An experimental study on the secondary flows and bed shear stress at a 90-degree mild bend with and without triangular vanes
Journal of Hydro-environment Research ( IF 2.8 ) Pub Date : 2020-10-20 , DOI: 10.1016/j.jher.2020.10.001
Mohammad Bahrami Yarahmadi , Mahmood Shafai Bejestan , Stefano Pagliara

River outer bank erosion and associated inner bank sedimentation cause river morphological and environmental changes. Triangular vanes are eco-friendly structures used for protection of river bank from erosion and morphological changes, fish passage improvement, and also fish habitat enhancement. In the present study, the 3D velocity components at a mild 90-degree channel bend were measured via an electromagnetic velocity meter with and without installed triangular vane. These tests were conducted at a Froude number of Fr = 0.214. The analysis of data showed that the triangular vane decreased the bed shear stress near the outer bank at the upstream and downstream sections of the vane for a distance of about 11 times the effective length of the vane. The maximum reduction at the upstream and downstream of the structure was calculated to be 67% and 80%, respectively. The strength of the vane-induced secondary flow was greater than that of the bend-induced secondary flow. At the position of 0.8L in the structure's downstream, the strength of the vane-induced secondary flow was maximum, after which started reducing and reached the strength of the bend-induced secondary flow at the position of 7L in the structure's downstream.



中文翻译:

带有和不带有三角形叶片的90度缓和弯道的二次流和床层剪应力的实验研究

河流外岸侵蚀和相关的内岸沉积引起河流的形态和环境变化。三角形叶片是一种生态友好的结构,用于保护河岸免受侵蚀和形态变化,改善鱼类通过以及鱼类栖息地。在本研究中,在有和没有安装三角叶片的情况下,通过电磁速度计测量了90度缓和通道弯曲处的3D速度分量。这些测试以Fr = 0.214的弗劳德数进行。数据分析表明,三角形叶片减小了叶片上游和下游部分外堤附近的床层剪切应力,其距离约为叶片有效长度的11倍。经计算,该结构上游和下游的最大减少量分别为67%和80%。叶片引起的二次流的强度大于弯曲引起的二次流的强度。在0.8的位置在结构下游的L处,叶片引起的二次流的强度最大,此后开始降低,并在结构的下游7 L处达到弯曲引起的二次流的强度。

更新日期:2020-11-21
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