Experimental and Numerical Investigation of Flow in a Newly Developed Vortex Drop Shaft Spillway

A new shaft spillway composed of an inlet structure that includes inlet swirling-flow-generating piers, an annular weir, a vertical shaft, and an outlet structure is presented. Major factors influencing the inlet's discharge coefficient, including the number of piers, pier weir angle, weir head, and pier height are discussed. An empirical discharge coefficient equation using a relative dimensionless weir head is presented in order to provide design guidance. Model experiments and numerical simulations are conducted regarding the flow behavior of the proposed inlet and vortex drop structure performance. Hydraulic characteristics such as the flow pattern, air core distribution, annular hydraulic jump position, pressure profiles, and water profiles of the outlet tunnel are obtained and agree well with the measured experimental data. Results show that the flow around the inlet is divided into a free-flow swirling region near the piers and submerged-flow region at the piers. The flow rate grows nearly linearly with the relative dimensionless weir head in the submerged region, and the discharge coefficient is approximately constant at 0.223. Experiments and simulations reveal the rotational flow movement mechanism of the self-regulating underwater swirl piers and the energy dissipation of the new vortex drop shaft spillway. Analytic calculations for the resultant velocity and water course thickness of the shaft sections correlate well with the results of a numerical simulation.