Bubble-induced turbulence modeling for vertical bubbly flows

Eulerian two-fluid model (TFM) has been the workhorse for several applications involving vertical bubbly flows due to its computational efficiency especially when applied to large-scale systems. The constituent phases are treated as interpenetrating continuous media, and the stress terms are usually modeled using Large Eddy Simulation (LES) and Reynolds Averaged Navier Stokes (RANS) approaches. Turbulence in the liquid phase plays an important role in determining the void fraction distribution. Besides, turbulence parameters are used in the closure models for interfacial terms which would determine heat and mass transfer or species composition in a given system. Hence, it is necessary to model the turbulence field accurately. LES-TFM approach has produced reasonably accurate results, albeit the sub-grid scale modeling of interfacial terms remains to be validated. There is a lack of a universal approach to model turbulent bubbly flows using RANS-TFM, and the research in developing the transport equations and closure terms is extensive. At present, the choice of one model over the other is mostly ad hoc, and a systematic analysis is required to determine their applicability. In the current review, the different BIT models and their applications have been summarized. Further, some of the shortcomings in the existing approaches are identified and recommendations for future work are made based on the analysis.