Aeroacoustic Assessment of Wind Turbine Blade Tips

Abstract

The trend to large wind turbines with increased blade diameters requires efficient noise reduction to increase public acceptance and to avoid further limitations in land use or shut-down times during night. Within the German national wind energy project BELARWEA improved methods to support the design of both, aerodynamically efficient and low-noise, wind turbine rotors are developed and validated. Aeroacoustically driven 2D profile design, 3D winglet design and 2D/3D CFD and CAA analysis are supplemented by the transfer of passive noise reduction technologies from aerospace applications to wind turbine blades. Experimental demonstration and tool validation is provided in systematic evaluation steps, (i) at 2D blade sections in the Acoustic Wind-Tunnel Braunschweig (AWB) of DLR, and (ii) at 3D blade tips in the larger acoustic facility DNW-NWB, operated by the German-Dutch Wind Tunnels foundation. The current paper provides a general overview of the DNW-NWB experiments and available validation data. Beyond this, the focus is set on the aeroacoustic evaluation of a new profile contour RoH-W-18%c37 (vs. NACA 64-618 reference profile) in the 2D as well as 3D test environments. The DNW-NWB tests were conducted on two 1:6 blade tip models in both the closed (3.25 m x 2.80 m) and ¾-open wind-tunnel test sections. Numerical results from a largely non-empirical hybrid CFD/CAA airfoil noise prediction approach, as applied during the profile design process, show excellent agreement with the finally measured 2-4 dB reduction of maximum sound pressure levels.