CFD simulation of bubble column flows: Investigations on turbulence models in RANS approach

CFD simulations of gas–liquid flows have been carried out in a full 3D, unsteady, Euler/Euler framework by means of the commercial software FLUENT®, and discussed in connection with laboratory scale bubble columns, with a particular interest in churn-turbulent flows. The importance of the choice of third order numerical schemes for such simulations was illustrated, as significant errors due to numerical diffusion can be induced by other less-stringent numerical set-ups. The available choices for turbulence modeling in RANS approach were tested following 9 different options, i.e., three possible formulations of the k–ε model (Standard, RNG, Realizable) combined with three different modalities to account for gas-phase effects (Dispersed, Dispersed+Bubble Induced Turbulence, Per-Phase). The Standard and Realizable versions of the k–ε model were unable to reproduce the expected gulf-stream patterns of bubble columns. However, the RNG k–ε model has exhibited much better descriptions of the flow features. The inclusion of bubble-induced terms in the turbulence equations led to minor impact on the performance of RNG k–ε models. The superior performance of RNG k–ε models essentially lies in the better depiction of the turbulent dissipation rate and turbulent viscosity. Thus, the application of RNG k–ε models would be also recommended for a further implementation of bubble population balance models.