Numerical modeling of hydraulic jumps at negative steps to improve energy dissipation in stilling basins

The performance of stilling basins including a negative step was analyzed addressing its effect on the energy dissipation efficiency, dimensions and structural properties of the hydraulic jump, streambed pressures and pressure fluctuations. Six different cases were simulated, considering two possible relative heights for the step and three possible Froude numbers. The results show that the step yields to lower subcritical depths, allowing smaller basin dimensions. Nevertheless, it tends to slightly increase the roller length of the jump. Concerning the relative energy dissipation, results confirm the improvement derived from the step presence. The internal flow occurring in the jump was also analyzed, and more specifically the subzones generated upstream and downstream the impingement point. The results prove the contribution of the negative step in the stabilization of hydraulic jumps in the stilling basin. In particular, a general decrease of the streambed pressure is observed. In addition, pressure fluctuations are significantly reduced due to the negative step size influence on the hydraulic jump. Furthermore, the effectiveness of the computational fluid dynamics (CFD) techniques to simulate stilling basin flows and to adequately characterize the hydraulic jump performance was confirmed.