Evaluation of Turbulence Models for the Design of Continuously Adapted Riblets

摘要

The extensive investigations during the last decades have verified the potential of ideal shaped riblet geometries for viscous drag reduction in the turbulent boundary layer.Basic requirement is an adaption of the riblet dimensions in terms of the local flow conditions.However,due to the complex manufacturing process of micro-scale surface structures most experimental measurements were conducted using riblets with constant dimensions.Therefore,the drag reducing potential of riblets could not be exploited.Thanks to the rapid development in micro structuring technologies it is now possible to manufacture continuously adapted riblets in almost industrial processing scales.To determine an appropriated area for the riblet application and continuously adapted riblet dimensions for the National Renewable Energy Laboratory(NREL)airfoil S809 information on the location of the laminar-turbulent transition and the wall shear stress distribution are required.For this purpose,numerical simulations were conducted using the transitional kkL-ωandγ-ReΘturbulence models as well as the fully turbulent SST implementation.Both transitional models show a sufficient precise prediction of the transition onset location in comparison with experimental data.Depending on the applied turbulence model computed riblet dimensions exhibit a certain deviation whereby a significant effect on the drag reduction can be expected.