Develompent of a modeling approach for bubble entrainment

This final report presents the work done for the numerical prediction of the plunging jet configuration including the air entrainment below the surface by the jet. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model. For example the air is a continuous phase above the water level but bubbly below the water level. Various drag models are tested and their influence on the gas void fraction below the water level is discussed. For the quantification of the gas entrainment and for the description of the plume geometry diverse measures are developed. The results of simulations are compared with experimental correlations and are discussed with respect to physical plausibility, e.g. in terms of mass conservation, bubble entrainment and the penetration depth of the gas plume below the water level.
If the gas is treated as dispersed phase everywhere in the domain and the grace drag law is applied, the gas entrainment is overestimated substantially. The algebraic interface area density (AIAD) model applies a drag coefficient for bubbles and a drag coefficient for the free surface. If the AIAD model is used for the simulation of impinging jets, the gas entrainment depends on the free surface drag coefficient. The gas entrainment can be controlled (tuned) via this parameter. So the AIAD approach can be used in future for the implementation of models (e.g. correlations) for the gas entrainment, since the physical details of the bubble generation generally can not be resolved in Euler-Euler simulations of large multiphase configurations.