Flow and Bed-Shear Magnification Downstream of a Barrage with Swirl Generated in Ducts by Stators and Rotors

Abstract

In this paper, the flow and bed shear stresses downstream of a tidal barrage, with open ducts and with swirl created by stators and rotors, are investigated experimentally. The wake created by open ducts is significantly three-dimensional within 20-duct diameters (20D) from the barrage. Within 20D of the barrage, the duct blockage and swirl also affect flow patterns and bed shear stress. Swirl affects jet mixing and local downstream circulation within 5-duct diameters (5D), resulting in large-scale cross-stream circulation further downstream. After 20D, the flow becomes predominantly parallel and depth averaging would be appropriate. Bed shear stress just downstream of the barrage is magnified by up to 3, 7, and 12 times, respectively, for open ducts, stators alone, and rotors plus stators. This has major implications for sediment motion and scour.