Numerical Simulation of Flow in the USBR II Stilling Basin with Converging Walls and End Steps

The stilling basins are of the most important energy dissipater structures, and changes in their shape lead to a better ‎hydraulic performance of them. In this study, the impacts of steps at the end of USBR II stilling ‎basin of Nazloo-Chay ‎dam and walls convergence on the pressure, water surface profile, efficiency of ‎hydraulic jump and energy dissipation ‎were investigated. For this purpose, the flow was ‎simulated using the VOF method and RNG turbulent model in ‎the ‎converging stilling basin (with convergence angle of 5◦, 7.5◦, 10◦ and 12.5◦) and discharge rate of 830 m3/s. The ‎numerical model was ‎verified by pressure's experimental data. The results showed that existence end steps and ‎convergence walls led to an increase in tail water depth and prevented hydraulic jump from exhausting out of ‎stilling ‎basin. Also, the convergence walls caused the jump to be submerged contrary to the free jump occurring in ‎stilling basins with parallel walls having free jumps. Convergence Walls had a positive impact on the efficiency of the ‎hydraulic jump. In this study, the converging stilling basin with 5◦ convergence angel gave a great performance, and the ‎efficiency increased by 136% in comparison to stilling basin with parallel walls. The comparison of the ‎results of energy ‎dissipation for different sections of stilling basin at different flow depths ‎demonstrated that the maximum energy ‎dissipation occurred in the depths between 20-30% of flow depth. These results may be considered for improving the ‎stilling basins design.‎