Revisiting RANS turbulence modelling for bubble-induced turbulence: effects of surfactants

Because of its high interfacial area density and mixing efficiency bubbly flow are utilized in diverse technical applications to enhance the interfacial mass and heat transfer rate. However, due to the superposition of complex shape variation as well as bubble-bubble interaction, many aspects concerning the effect of bubbles on the bulk flow remain unclear, and bubble-induced turbulence (BIT) is one of them. In the past great effort has been made towards the BIT modelling in the framework of two-equation turbulence models, but the understanding of physics is still far from satisfactory. This work revisits the model proposed by Ma et al. [Phys. Rev. Fluids 2, 034301 (2017)], which considers the BIT with an additional source term in the k- and epsilon" (or omega)- equation, respectively, and has been widely adopted in the simulations of bubbly flows.
Recent experiments show that contamination of the carrier phase plays a considerable role in BIT: although the bubbles rise slower with adding surfactants, the BIT increases. This trend cannot be reproduced by any current BIT models, including Ma et al. (2017). We have further investigated the reason for this and discuss the new possibility for the prefactor in the source term of the "epsilon-equation that may improve the results.