Comparative assessment of turbulence models for high-velocity two-phase flow over a chute spillway aerator

ABSTRACT

Schematic diagram of a chute spillway aerator showing three flow phases: continuous water, air-water cavity, and dispersed bubble mixture, with labelled zones and flow directions.

Aerator-induced two-phase flow on high-velocity chute spillways involves complex air–water interactions insufficiently resolved by conventional Reynolds-averaged Navier–Stokes (RANS) models. This study presents a systematic comparative assessment of 2D and 3D CFD models employing detached Eddy simulation (DES), delayed detached eddy simulation (DDES), and the realizable k–ε turbulence closure within mixture and Eulerian multiphase frameworks, supplemented with the Schiller–Naumann (S&N) drag model. All models are thoroughly used on the experimental data. In the 2D framework, the Eulerian realizable k–ε model best reproduces experimental jet length, unit air discharge, and air–water flowrate ratio, whereas 2D DES and DDES substantially overestimate these parameters. All 2D models systematically overestimate near-bottom air concentrations and underestimate the cavity zone, attributable to their inability to resolve three-dimensional flow structures, lateral air distribution, and secondary recirculation. The transition to 3D formulation result in an improvement in the predicted jet length of 0.13 m and air discharge of 0.125 m2/s and deliver superior predictions of flow bulking, velocity profiles, turbulent kinetic energy (TKE) topology, and near-bottom air concentration. TKE analysis confirms that DES and DDES resolve large-scale coherent eddy structures impingement vortices that the realizable k–ε model systematically suppresses under its inherent turbulence-uniformity assumption.