Abstract:
Air entrainment is common in free surface flows in large hydraulic structures (e.g., spillways, chutes, energy dissipation structures) and must be considered to assure an effective and safe
operation. Due to the large size of the prototype structures, it is infeasible to model individual
air bubbles. Therefore, using the OpenFOAM toolbox, an efficient simulation model for aerated
flows is developed for engineering purposes. The Reynolds-averaged Navier–Stokes equations and
the volume-of-fluid method are coupled with a sub-grid bubble population model that simulates
entrainment and transport. A comprehensive assessment of the effectiveness, computational cost,
and reliability is performed. Local and continuum bubble entrainment are evaluated in two distinct
flows: an impinging jet and along a spillway chute. Aeration is induced, respectively, by a shear flow
and by the thickening of the turbulent boundary layer. Moreover, a detailed sensitivity analysis of
the model’s parameters is conducted. Calibration and validation are performed against experimental
and prototype data. Among the analyzed entrainment formulations, the one depending exclusively
on the turbulent kinetic energy is the only applicable to different flow types. Good accuracy is
found, meeting engineering standards, and the additional computation cost is marginal. Results
depend primarily on the volume-of-fluid method ability to reproduce the interface. Calibration is
straightforward in self-aeration but more difficult for local aeration.
