Experimental study on the body parameters of the two-stage stilling basin in low Froude number flow

Under the condition of a low Froude number (Fr) flow, the two-stage stilling basin is an effective way of solving the problem of energy dissipation. However, to date, there have been many applications of the two-stage stilling basin, but little research on the shape parameters and energy dissipation mechanisms. To address this issue, the body parameters and their sensitivity in the two-stage stilling basin during low Fr flow were studied by combining theoretical analysis and a physical model. The results indicated that the parameters of the stilling basin such as length, depth, and end sill height all have thresholds. When a parameter exceeds the threshold, the undular or repelled downstream hydraulic jump tends to occur in the first stage stilling basin, while the water surface fluctuation in the second stage stilling basin increases significantly. When the length of the stilling basin is less than the threshold, the flow regime in the stilling basin deteriorates, and the energy dissipation ratio decreases significantly. The lower the height of the end sill, the better the wave attenuation effect. The energy dissipation ratio of the optimized two-stage stilling basin is obviously improved, and the adaptability to the tail water level is also significantly expanded. In this study, the correction coefficient (ω_i) of the end sill is introduced, and the formula for calculating the length as well as the end sill height of stilling basins is proposed.