Drag Evaluations on Rough Surfaces From Near-Wall Models

Abstract

In this paper we evaluate the drag of periodic rough microstructures from near-wall models. With near-wall models we denote Coutte flows which describe the viscous boundary layer of turbulent flows. The structures inside this layer are not the optimal ones but can be used for a deeper understanding of the drag reducing mechanism of riblets due to a valid mathematical theory for viscous flows. Here, the numerical calculations can be validated and the developed calculation strategies can later be extended to the turbulent boundary layer. The focus of this paper is the evaluation of the drag of several microstructures for a better understanding of their action to the turbulent overflow. The influence of the structures will be visible trough a shift in the mean velocity profile which will be quantified. Due to the fixed calculation domain and thus an altered sublayer thickness, the obtained drag values can not be easily compared. We will as well present a theory for the comparison of the drag of rough surfaces calculated from our near-wall models as one for the comparison of rough versus smooth surface.