Engineering Applications of Computational Fluid Mechanics (Jan 2018)
Rough boundary treatment method for the shear-stress transport k - ω model
Abstract
Most of existing rough boundary treatment methods for the shear-stress transport $ k - \omega $ model require much finer grids than smooth boundary treatment methods. Knopp, Eisfeld, and Calvo (2009, A new extension for k–ω turbulence models to account for wall roughness. International Journal of Heat and Fluid Flow, 30(1), 54–65.) developed a rough boundary treatment method that allows the same grid resolution as smooth boundary treatment methods, but its effect of grid resolution on the computed velocity is strong. This study aims to improve the method of Knopp et al. (2009, A new extension for k–ω turbulence models to account for wall roughness. International Journal of Heat and Fluid Flow, 30(1), 54–65.) and to reduce the effect of grid resolution. This work newly incorporates the effect of grid resolution on boundary values of $ {\omega } $ , the inverse time scale. The method generates the logarithmic velocity profile of open channel flows over rough beds with a velocity shift relative to that over smooth beds. The computed velocity shift, depending on the dimensionless roughness, generally agrees with the measured ones. The effect of the grid resolution on velocity shift that is computed using the present method is only 31% of that using the method of Knopp et al. (2009, A new extension for k–ω turbulence models to account for wall roughness. International Journal of Heat and Fluid Flow, 30(1), 54–65.) in the transitionally rough regime. The effect of grid resolution in the transitionally rough regime is stronger than in both the hydraulically smooth regime and the fully rough regime. The present method is applied to simulate open channel flow over a bed with suddenly changing roughness. The computed velocities are consistent with the measured ones. The method reveals a sharp response of the shear velocity to the sudden change in roughness.
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