| A jet that flows parallel, and in close proximity, to a free-surface such that the jet behavior is influenced by the free-surface is defined as a surface jet. A surface jet attracts water from the surroundings and the phenomenon is called water entrainment. This entrainment is found to be resulting from the combined effects of momentum transfer, streamwise vorticity and the resulting surface current, the Coanda effect and presence of a two-phase gas/liquid flow.; Strong water entrainment has been observed downstream of spillways with flow deflectors. These deflectors are installed to create surface jets thereby reducing total dissolved gases by limiting the penetration depth of spillway jet. The resulting water entrainment has several important environmental, engineering and ecological impacts. It improves mixing of powerhouse and spillway flows affecting the temperature distributions and concentrations of oxygen and other dissolved gases. It may negatively impact migratory fish passage or create adverse flow conditions for navigation and recreation.; Most studies found in the literature attribute water entrainment to turbulent mixing. Aeration and free-surface instabilities modify the turbulence structure and influence entrainment. Reduced-scale hydraulic models and standard single-phase, isotropic RANS numerical models under-predict entrainment observed in field measurements. This thesis presents an anisotropic model accounting for the bubble volume fraction and normal velocity fluctuation attenuation at the free surface. The model adequately predicts the main causes of water entrainment. It compares well with laboratory data for a round surface jet, model scale and prototype scale data from hydropower installations. Comparisons of computational fluid dynamics simulations using isotropic and anisotropic turbulence models are presented. These show that entrainment can be captured if turbulence anisotropy and the two-phase nature of the flow are properly modelled. |
