Inflow Turbulence and Leading Edge Roughness Effects on Laminar-Turbulent Transition on NACA 63-418 Airfoil

Abstract

The surface imperfections and the inflow turbulence in real operational conditions can cause significant deviations from the predicted wind turbine aerodynamic performance and energy yield. In this study, particular emphasis was placed on the effect of these parameters on the laminar-turbulent transition on wind turbine blades. For this purpose, the DAN-AERO wind tunnel measurements, with high frequency microphones flush mounted on the both suction and pressure sides of the NACA 63-418 airfoil profile, were used. Typical operating condition Reynolds numbers, turbulence grid and boundary layer control devices on the surface were implemented. The results indicate a high dependency of the transition process on these parameters. The analyses show that the critical height of the leading edge roughness (LER) is to be met in order to have a bypass transition to turbulent flow at the angle of attacks, where the stagnation point is upstream of the LER location. The transition location moves closer to the leading edge with increasing Reynolds number when the roughness height is smaller than the critical height. Inflow turbulence is observed to have a larger effect on the transition location than the predicted numerical results.