Author(s): Xiaofeng Liu; Detian Liu; Hongbo Ma; Manjure M. M. Nayamatullah; Xudong Fu
Linked Author(s): Hongbo Ma, Xudong Fu
Keywords: Suspended sediment transport; Low Reynolds number modeling; Boundary layer
Abstract: For boundary-layer resolving models, a suitable boundary condition is needed for suspended sediment. For most of empirical formulas, the equilibrium concentration is specified at certain reference height. There is a gap between the wall and the reference height. This is the reason that most numerical models have to use ad-hoc treatment to close this gap. In a previous paper, we have discussed how to deal with this gap in models with wall functions where a boundary condition can be applied directly to the wall. Both the fluid and the suspended sediment are solved on a unified mesh. In this paper, we extend the same methodology to boundary-layer resolving models, such as low-Reynolds number (LRN) models. In these models, the viscous-sublayer and the buffer layer are resolved. Based on the near-wall turbulent flow structure at equilibrium condition, the governing equation for suspended sediment is integrated from the reference height to the wall and new wall boundary conditions can be derived. Roughness effect, which is important for sediment bottoms, is fully considered. The merit of using this near-wall treatment is the elimination of the need to use two different meshes for fluid and sediment and the reduction of accuracy loss. More importantly, dynamic exchange of sediment mass across the bottom can be evaluated correctly in the boundary-layer resolving models. The new near-wall treatment has been implemented in OpenFOAM and an example will be given.