Abstract
The turbulent flow close to a wall with two-dimensional roughness is computed with a two-layer zonal model. For an impermeable wall, the classical logarithmic law compares well with the numerical results if the location of the fictitious wall modeling the surface is considered at the top of the rough boundary. The model developed by Wilcox for smooth walls is modified to account for the surface roughness and gives satisfactory results, especially for the friction coefficient, for the case of boundary layer suction.
Highlights
Numerical modeling of turbulent flows is continuously progressing, some questions remain open and need further investigation in many practical situations
Patel1͔ underlines ‘‘the uncertainty in the dependence of ⌬B on the size and type of roughness and in the effective location of the fictitious wall, from which the distance is measured.’’ Patel showed some inadequacy of the logarithmic law for modeling a turbulent flow over a wavy wall, which can be considered as a kind of rough surface and application of the wall-function approach is questionable for this type of surfaces
Assuming the same physical process for rough surfaces with suction, we propose to modify the law of Wilcox by replacing yϩ by y/ks in Eq ͑19͒
Summary
Numerical modeling of turbulent flows is continuously progressing, some questions remain open and need further investigation in many practical situations. When a rough wall is considered, the velocity profile is well described by introducing a shift, called the roughness function and denoted ⌬B, in the logarithmic law of the wall, ͓2,3͔ Such a wall-function approach is desirable in many situations since it avoids detailed computations of the flow in the viscous sublayer and in the buffer layer and saves large computation time. Patel1͔ underlines ‘‘the uncertainty in the dependence of ⌬B on the size and type of roughness and in the effective location of the fictitious wall, from which the distance is measured.’’ Patel showed some inadequacy of the logarithmic law for modeling a turbulent flow over a wavy wall, which can be considered as a kind of rough surface and application of the wall-function approach is questionable for this type of surfaces
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