Analysis of riblets performance in pressure gradient flow by Large Eddy Simulation

The effectiveness of riblets in reducing friction drag has been well assessed by many experi- ments in flat plate and channel flow in the end of the last century. Both theory and experiments showed that the effect of riblets only depends on the local Reynolds number, however some experiments in pressure gradient flow showed increased effectiveness of riblets. This effects are still debated because a physical motivation on the effect of riblets on form drag was not provided. Recently a model based on slip length concept for riblets simulation at high Reynolds numbers has been proposed in RANS solver, providing a contribution to understanding the origin of the increased effectiveness of riblets in pressure gradient flow. In the present paper the model is extended to Large Eddy Simulation methods and applied to the analysis of airfoil flows. The analysis provides a reliable analysis of the effect of pressure gradient on riblet performance.