Abstract: The flow circulation and flow energy exchange in the concave angle of stepped spillway is a key factor of flood discharge and energy dissipation. Current research of stepped spillway mostly focus on the combined actions of step’s slope and size as well as wide tail pier; the geometric shape of concave angle is rarely studied. In this paper, the flow pattern, flow velocity, intensity of pressure and concentration of entrained air in both traditional triangular concave angle steps and trapezoidal concave angle steps are examined via hydraulic model tests and numerical simulated calculations. Results demonstrated the similarity of flow state between trapezoidal concave angle steps and traditional triangular concave angle steps; but trapezoidal concave-angle step changes the shape of vortex shedding, which, therefore, moves into the main flow and promotes the turbulence of water flow. As a result, the initial point of aeration moves slightly forward, the average concentration of entrained air in the cross section of the main flow area increases, the total pressure fluctuation at the virtual bottom plate intensifies, and the average flow velocity of the step section reduces, beneficial to reducing the risk of step cavitation and promoting the energy dissipation of the step.

Key words: hydraulic characteristics, stepped spillway, trapezoidal concave angle step, model test, numerical simulation