A mesoscale bubble-induced turbulence model and simulation of gas-liquid flows

In gas-liquid two-phase flows, bubble motion significantly affects liquid-phase turbulence, and adding bubble-induced turbulence (BIT) source term is widely used to improve the simulation accuracy. This paper presented a new BIT model based on the energy-minimization multi-scale (EMMS) methodology. The model was constructed by considering two mesoscale factors, i.e., the sub-grid structures through analyzing the slip velocity and the gas holdup gradient, and the equivalent diameter of turbulent eddies calculated by the EMMS-based turbulence model. In order to verify its performance, the model was incorporated to the Eulerian-Lagrangian simulating framework and applied to two typical experimental systems. Both mean flow characteristics and turbulence quantities were well predicted, and the new model showed advantages over traditional BIT models, especially at higher gas velocities. Moreover, a strategy for counting energy dissipation in the simulation was devised and performed, whereby the dual effects of promotion and suppression on liquid-phase turbulence by bubbles can be reflected. The simulations demonstrated that BIT dominated the energy dissipation and turbulence was enhanced by BIT at higher gas velocities, while shear-induced turbulence (SIT) dominated the energy dissipation and turbulence is reduced due to the suppression by bubbles at lower gas velocities.