An experimental study on the secondary flows and bed shear stress at a 90-degree mild bend with and without triangular vanes

Abstract

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.