Modeling of the free-surface vortex driven bubble entrainment into water

The recently developed GENTOP (Generalized Two Phase Flow) concept which bases on the multi-field Euler-Euler approach was applied to model a free-surface vortex - a flow situation which is relevant for hydraulic intake. A new bubble entrainment model has been developed and implemented in the concept. In general a satisfying agreement with the experimental data can be achieved. However, the gas entrainment can be largely affected by several parameters or models used in the CFD (Computational Fluid Dynamics) simulation. The scale of curvature correction C_scale in the turbulence model, the coefficient in the entrainment model C_ent and the assigned bubble size to be entrained has significant influence on the gas entrainment rate. The gas entrainment increases with higher C_scale which can be attributed to the stronger rotation captured by the simulation. A smaller bubble size gives higher gas entrainment while a larger bubble size leads to a smaller entrainment with a periodical peak of entrainment in its transient profile. The results also show that the gas entrainment can be controlled by adjusting the entrainment coefficient C_ent. Basing on the modeling framework presented in this paper further improvement on the physical modeling of the entrainment process should be done.