Numerical modelling of turbulent flow patterns performance in boundary layer separation during hydraulic jump in the stilling basin

Energy dissipation downstream of large dams spillways is a serious problem. The water flow, which passes over the spillway crown downward, has many hydraulic characteristics. Among these characteristics, one could refer to the flow over the spillway and transfer from the supercritical to the subcritical state and the hydraulic jump (energy dissipator), also transfer of the flow from the subcritical flow to the normal water surface in the river. All these indicate the way the upstream and downstream parts are connected in a hydraulic structure. A general type of these structures is the stilling basin. As laboratory modelling for all assessment cases often takes much time and is costly, therefore in this research the capabilities of FLUENT 15, which is a computational fluid dynamics software, are utilized. This software simulates the governing fluid flow equations including the Navier-Stokes continuity and motion equations using the finite volume method in each time step. Investigating the performance of turbulent flow patterns in separation of the boundary layer in the hydraulic jump within the stilling basin of Nazloochai Dam laboratory model has been among the goals of this research. In this respect, simulation for the four turbulence models of Standard κ – ε, RNG κ – ε, realizable κ – ε and Reynolds- stress, by incorporating the case of standard wall functions and applying the design discharge has been performed. The results show that in the initial zone of jump, due to the high turbulence of flow, the computed values are somehow different with respect to the measured ones. However, this difference is greatly decreased at the end of jump due to the reduced turbulence in flow. Both turbulence models of Standard κ – ε and RNG κ – ε exhibited precise results in terms of the water surface profile. In this research it was found that the κ – ε turbulence model has a good performance and accuracy in determining the water surface profile.

Keywords:

hydraulic jump , Eulerian fluids , Navier-Stokes , VOF , energy dissipation , turbulence model