LES of Turbulent Co-current Taylor Bubble Flow

Abstract

Turbulent co-current Taylor bubble flow was modeled with LES alongside the VOF interface tracking solver. The method is first validated in the context of single phase turbulent pipe flow and three distinct laminar Taylor bubble flow cases. The turbulent co-current Taylor bubble flow is simulated using a moving frame of reference which is attached to the bubble, allowing for a straight-forward time averaging and Dirichlet-type flow recycling inlet boundary condition. In contrast to periodic inlet and outlet boundary conditions, the Dirichlet one assures that small bubbles which are lost by the Taylor bubble are removed from the computation once they leave the domain, therewith not interfering with the nose of the Taylor bubble. The transient loss of small bubbles which is observed in our simulations implies that the problem is inherently unsteady. We therefore present an averaging strategy which consists of combined time, space and ensemble averaging. This strategy allows systematic comparison of results across different computational meshes. The results show that the approach captures distinct features of turbulent co-current Taylor bubble flow well, in the sense that good agreement is observed with experimental data from literature in terms of the toroidal vortex flow field in the wake of the Taylor bubble. Agreement with measured velocity fluctuation profiles in the wake of the Taylor bubble is less pronounced, and is discussed in the paper. Nevertheless, the simulation approach of co-current Taylor bubble flow proposed in this paper may serve as a tool that will provide deeper insights in two-phase turbulent flow for future research.