Flow characteristics and energy dissipation over stepped spillway with various step geometries: case study (steps with curve end sill)

Abstract

Stepped weirs are used in a wide range of applications, designed to increase energy dissipation. In this study, laboratory experiments were conducted in a flume on six stepped weir models, with a downstream angle of θ = 26.6°. The physical models used were on a scale of 10:1, and tests of discharges up to 0.055 m³/s were carried out. Several step geometries including traditional step, sill and curve geometries were used to study flow behavior and overall energy dissipation. The laboratory investigations were augmented by modelling numerically the within step flow and energy behavior using a 2-D CFD model, incorporating the k-ε model for turbulence closure. The results showed that energy dissipation was greatest for the curved steps by about 10.5%, where it was observed that the skimming flow regime was shifted to a higher discharge range. Numerical modelling results showed good agreement with the experimental results. An inspection of the modelled streamlines highlighted the increase in vortex intensity for the curve model, reflecting the strong circulation observed. The predicted stepwise energy dissipation showed the energy dissipation increase when the step number N_s increases. For the range of step height h_s, tested, our results showed that energy dissipation increased with step height. The results from this study can be used to inform engineering design for steps with θ = 26.6° and provide estimates of the expected energy dissipation and residual energy.