The effects of increased Reynolds number (Re) on clean and rough airfoils were investigated by wind tunnel experiments and by numerical simulation with an improved Navier-Stokes solver. By cooling the cryogenic wind tunnel in Cologne (KKK) of the German-Dutch Wind-Tunnel (DNW) down to 100 K, values of Re up to 10 × 106 were reached, based on a model chord of 500 mm. Whereas the clean surface configuration shows no drastic loss in maximum lift, the lift-to-drag ratio decreases from 95 to approximately 85, mainly due to an increase of drag. In contrast to that, rough surface configurations, including zig-zag tape for transition fixing and carborundum based distributed roughness around the nose, show increased performance for increased Re. In parallel, numerical simulations were carried out with a boundary layer stability code coupled to a Navier-Stokes solver. The trends in behaviour of the boundary-layer based properties were predicted well, in contrast to the separation pattern responsible for maximum lift.

This paper describes some effects on the load level of state-of-the-art multi-megawatt wind turbines introduced by the new edition of the

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