A two-equation turbulence model of turbulent bubbly flows

A two-fluid model of turbulent, adiabatic bubbly flow was implemented in th e computational fluid dynamics (CFD) CFX4.2 program and validated. Turbulen ce in the dispersed (bubble) phase was neglected. Liquid turbulence was mod eled through a two-phase extension of the single-phase standard k-epsilon m odel. Conservation equations of turbulent scales contain single-phase and i nterfacial terms. A closure for the interfacial turbulence terms was propos ed based on the assumption of low-bubble inertia and neglecting surface ten sion. The interfacial turbulence terms account for additional pseudoturbule nce in liquid created by bubble-induced mixing. The proposed turbulence mod el contained the single empirical constant in the modeled dissipation rate balance. The model was implemented in the CFX4.2 commercial CFD solver. Com paring numerical predictions to the experimental data the value of the mode l constant was estimated. Model predictions were compared to other bubbly f lows to prove the universality of the model constant. The comparison showed that the constant has a certain generality. A new, two-phase logarithmic w all law was also implemented and validated. The derivation of the new law w as based on an assumption of the additional eddy diffusivity due to the bub ble-induced stirring in the boundary layer. An improved wall friction predi ction was achieved with the new wall law over conventional single-phase law . The improvement was especially noticeable for the low-liquid flow rates w hen bubble-induced pseudoturbulence plays a significant role. The ability o f the model to account for bubble size effect was also studied. (C) 2001 El sevier Science Ltd. All rights reserved.