Towards a General Strategy to Model Riblet Effects

For a realistic configuration, solving the flow details at the riblet level is beyond the capabilities of present computers. Therefore, a riblet model is needed to account for riblets in practical computations. A general strategy to sensitize turbulence models to account for riblets is proposed. Similar to models for flows over rough surfaces, the proposed model is made of two parts. First, the shift of the velocity profile is shown to be representative of the skin friction change due to riblets. This shift is modeled from experimental data for Uand V-shaped riblets as a function of the riblet geometry and characteristic Reynolds number. Second, ways to modify two popular turbulence models to reproduce this shift of the logarithmic region are proposed, which are based upon the model structure in the wall region.Model validation is performed using a boundary layer code for various shapes and flow conditions, leading to skin friction reduction as well as increase.