Tag Archives: bottom shear stress

Accurate vertical profiles of turbulent flow in z-layer models

F.W. Platzek, G.S. Stelling, J.A. Jankowski and J.D. Pietrzak

Abstract. Three-dimensional hydrodynamic z-layer models, which are used for simulating the flow in rivers, estuaries, and oceans, suffer from an inaccurate and often discontinuous bottom shear stress representation, due to the staircase bottom. We analyze the governing equations and clearly show the cause of the inaccuracies. Based on the analysis, we present a new method that significantly reduces the errors and the grid dependency of the results. Continue reading

On the representation of bottom shear stress in z-layer models

F. Platzek, G.S. Stelling, J.A. Jankowski, R. Patzwahl

Abstract. Bottom friction plays an important role in modelling river flows. In three-dimensional (3D) models, the vertical discretization is commonly based on σ-layers or z-layers. In this paper we focus on a well-known problem encountered when applying z-layers: local truncation errors in the computation of bottom shear stress and near-bed turbulence along a sloping bottom as e.g. in the case of 3D river simulations. This problem stems from the ‘staircase’ representation of the bottom and results in difficulties in the computation of morphological changes. Continue reading