Aeroacoustic Evaluation of Low-Noise Wind Turbine Blade Tips

The contribution provides an overview on accomplished wind tunnel testing and simulation activity within the German national wind energy project BELARWEA. The project aimed at numerical tool development and validation to support the design of both aerodynamically efficient and low-noise wind turbine rotors. The focus was set on the tip region, herein defined as the outer 20 % of the rotor radius, i.e. addressing noise generation from the trailing-edge- and tip vortex regions. Aeroacoustically driven 2D profile design, 3D winglet design and 2D/3D CFD/CAA analysis were supplemented by the transfer of passive noise reduction technologies from aerospace applications to wind turbine blades. Validation experiments were performed in systematic evaluation steps, namely - at 2D blade sections in the Acoustic Wind-Tunnel Braunschweig (AWB) of DLR, and - at 3D blade tip models in the larger acoustic facility DNW-NWB, operated by the German-Dutch Wind Tunnels foundation. A noise reduction potential of up to 8 dB could be demonstrated in the NWB experiment, confirming the previously documented AWB results. The overall reduction was composed of a 2-4 dB reduction by a new low-noise profile design RoH-W-18%c37 (relative to a NACA 64-618 reference configuration) and an additional ~4-6-dB reduction by brush add-ons