Author(s): Kasai Tomoaki; Nakayama Akihiko

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Abstract: Successful Large-eddy simulations (LES) of flows in hydraulic applications such as simulation of flows in natural rivers require appropriate boundary conditions to be applied on the bottom bed. Since it is impossible to resolve viscous sub-layers with computational grids that can be accommodated by most computer systems, a wall model that is applicable in general cases including those cases with rapid variations and flow separations, is required. Most wall models, however, are based on similarities and characteristics of flows over flat surfaces and their performance in predictions of more general flows is not known well. A few wall models that are commonly used have been tested against Direct Numerical Simulation (DNS) results and well-resolved LES simulation results of flows over periodic mound-like topography and wavy bed that involve flow separation and reattachment. The models tested are commonly used ones based on logarithmic-law and power-law similarities of instantaneous velocity distribution and used together with standard Smagorinsky and shear-improved Smagorinsky subgridscale models. In addition to these conventional models, a new model based on resistance law, in which the local and temporal wall stress is related to the total velocity at calculation points closest to the bottom boundary, is proposed and tested.

DOI:

Year: 2009