Abstract
Water transferring to the dam downstream creates high levels of kinetic energy. Stepped spillways are amongst the most effective spillways in reducing the kinetic energy of the flow moving towards the downstream. The geometry of the steps in stepped spillways can affect the reduction of kinetic energy of the flow transferring to the downstream. Therefore, in this study the effect of different number of steps and discharge on flow pattern especially energy dissipation were investigated. The VOF method was used to simulate the flow surface and the k-ε (RNG) turbulence model was used for flow turbulence simulation. Comparing the results obtained from the numerical simulation with the experimental data indicated an acceptable level of consistency. Comparing the obtained results showed that decreasing the number of the steps of pooled stepped spillways reduced flow velocity and increased the relative energy dissipation at the end of the spillway. Decreasing the number of steps increased the turbulent kinetic energy value. Also, the maximum turbulent kinetic energy was obtained near the step’s pool. Moreover the results indicated that the value of turbulent kinetic energy increased along the spillway.
Highlights
One of the objectives of designing spillways is to transfer water flow to the dam downstream
Guenther et al [20, 21] examined flow aeration and energy dissipation on a stepped spillway with 10 steps and 4 types of configurations. They came to the conclusion that pooled stepped spillways with staggered configuration of flat and pooled steps and pooled stepped spillways with in-line configuration of flat and pooled steps had not advantageous performance as pooled stepped spillways and flat stepped spillways regarding the matter of energy dissipation
The VOF method was used to simulate the water surface profile and k- ε(RNG) turbulence model was used for flow turbulence
Summary
One of the objectives of designing spillways is to transfer water flow to the dam downstream. Wuthrich and Chanson [22] examined gabion stepped spillways consisting of 10 steps with a 26.6 degree slope They compared their results with that of flat stepped spillways (with flat and impermeable steps) and showed that relative energy dissipation over flat stepped spillway was greater than of gabion stepped spillways in transition and skimming flow regimes. Xiangju et al [24] simulated a two-phase flow on a stepped spillway They examined the hydraulic parameters including velocity and pressure and compared the VOF and Mixture methods. Nikseresht et al [30] used the VOF and Mixture method and compared stepped spillways with different slopes They came to the conclusion that as the discharge increased, energy dissipation decreased for a given slope. The effect of the number of steps on energy dissipation, turbulent kinetic energy, and the flow pattern was examined
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