Towards LES of bubble-laden channel flows: Sub-grid scale closures for momentum advection

This paper presents an a-posteriori assessment of different LES sub-grid scale closures for momentum advection in the context of bubble-laden channel flows. The numerical approach is based on the Volume-of-Fluid method in combination with the onefluid formulation of the incompressible Navier-Stokes equations. To study the behavior of different subgrid scale models, a turbulent bubble-laden downflow channel is simulated at a friction Reynolds number of Re_Τ = 590. The setup is chosen such that the bubbles are nearly spherical, but mildly wobbling. Both functional models of eddy viscosity type and scale similarity type models are used to close the sub-grid scale stresses. The results are compared to a direct numerical simulation of the same setup. It is found that the stream-wise volumetric flow rate depends strongly on the closure model as well as the grid resolution. While some models lead to an improvement compared to the LES without an explicit model, the comparably dissipative nature of the QUICK scheme prevents a clear assessment of some more advanced modeling strategies.