Surface tension energy in bubbly flows physical impact and modelling in RANS Eulerian-Eulerian two-fluid model
Résumé
The Eulerian-Eulerian two-fluid model for turbulent bubbly flows has been extensively studied. Such a model has by construction inherent limitations because it relies on a particle approach. This method considersthe bubble as a pointwise particle without finite-size effects, which should be meaningful only when the characteristic length scale of averaged quantities variations is bigger than the bubble length scale. However,several physical phenomena such as the surface tension energy do not satisfy this criteria. Physical analysis based on Direct Numerical Simulations (DNS) of bubbly turbulent plane channels are performed with TrioCFD. In order to feed the RANS\footnote{Reynolds Average Navier Stokes} modelling, the upscaling process extracts knowledge from DNS. Then, new models are tested on the RANS Eulerian code Neptune\_CFD. In this work, the impact of surface tension energy is investigated.\\Firstly, the significant contribution of the surface tension source term in the momentum balance is demonstrated. In a RANS model, the forces applied on bubbles should be modelled, as well as the Reynolds Stress tensor. It is known that surface tension energy impacts both the turbulence and the forces through the deformability of the interface, but to the best of our knowledge, the interfacial momentum source termis never taken into account in a RANS model. The interfacial force is traditionnally splitted into several contributions such as drag, lift, added mass or turbulent dispersion force. Secondly, we demonstrated that the surface tension force has a behaviour similar to an equivalent turbulent dispersion force. Moreover,in some weakly turbulent cases and for large surface tension, the interfacialenergy has a significant impact on the bubble migration.
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