Flip buckets are commonly used in hydraulic structures with steep slopes such as spillways to discharge outflow away from the hydraulic structure and dissipate the excessive flow energy. Various types of this hydraulic structure are now in operation all around the world. Due to lack of generalized design guidelines, they are mostly designed based on some empirical equations and/or the results of some site-specific model studies. The powerful NavierStokes (NS) solvers have a good potential to simulate flows passing these hydraulic structures, and consequently can be applied by engineers as a complementary tool to better design of these structures. This could provide engineering with a preliminary knowledge about the physical processes that may occur inside these structures. In this paper a 2D RANS solver based on finite volume method was applied to model the flow characteristics over a flip bucket without deflector. Additionally, the VOF method was used to model the free surface. The common two-equation turbulence models of (k- and k-) were implemented and the results were compared with the experimental data. To check the accuracy of the results, three major hydraulic characteristics of simulated flow were compared with the experimental results. It includes the upper and lower jet trajectory, the approach velocity (upstream depth), and the bucket bottom pressure distribution. The results indicated that the laminar model did have the best agreement with experimental results. Moreover, due to dissipative nature of the two-equation turbulence models, the jet trajectory was underestimated using the k-epsilon and the k-omega models.

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