Mehdi Nomiri - M.Sc. Student of Hydraulic Structures, Azad University, South Tehran Branch, Faculty of Civil Engineering,Tehran, Iran
Elham Mina - Ph.D Student of Hydraulic Structures, Tarbiat Modares University, Faculty of Environmental Civil Engineering,Tehran, Iran
Mohammad Reza Kavianpour - Professor, Khaje Nasir-Al-Din Tusi University of Technology, Faculty of Civil Engineering, Tehran, Iran

The excess water behind the reservoir dams has a lot of energy when entering the river after passing through the spillway. If the energy is not decreased before entering the natural bed of the river, it will cause the dam downstream to be eroded. In such cases, it is necessary to use the energy dissipation structures of the stilling basin, which can be effective in controlling and dissipating the energy. Energy dissipation through a hydraulic jump is always accompanied by a fluctuating pressure on the floor of the stilling basin. Severe pressure fluctuations cause numerous damages to the facilities. Therefore, recognizing the phenomenon and its effect on the basin slab is of particular importance. Due to the considerable costs allocated in the design and implementation of these dams to the spillways and stilling basins, the optimal design of the basin was of great importance. Therefore, using Fluent 15 computational fluid dynamics (CFD) capabilities, the equations governing the fluid flow included in the Navier Stokes continuity and motion equations are simulated by finite volume method in each time step. The study of the improvement in the hydraulic performance of the flow pattern in the stilling basin with the geometric optimization mechanism of the laboratory model for Nazlouchay Dam in Urmia, Iran is the objective of this study. In order to achieve the goal, the simulation of free -surface two-phase flow was modeled using the turbulence model (k-ε) to achieve a suitable flow pattern. In this regard, in order to provide the conditions for the formation of hydraulic jump in the stilling basin for the discharges more than the design discharge as well as to optimize the dimensions of the basin in two conditions, the end-sill and the dentated adverse-slope dissipators were investigated for different flow rates. The results indicate that the application of the end sill instead of the adverse slope of the type-2 stilling basin tailwater has a good performance in the flow pattern, energy dissipation, and increased downstream depth. As the flow rate is increased, the minimum depth of the sections is decreased and the maximum depth is increased. This is because as the flow rate is increased, the jump moves downstream relative to the first measurement section.

Hydraulic jump, Eulerian fluids, Navier Stokes, VOF, energy dissipation, turbulence model