Novel acoustic measurements of a blade tip in a closed wind tunnel

Abstract

This paper presents novel acoustic measurements of a wind turbine blade-tip model in a closed wind tunnel test section, combining a wall-mounted array with a microphone configuration that effectively attenuates turbulent boundary-layer-induced wall pressure fluctuations, as well as four inflow microphones installed on opposite walls (two on each side), analyzed using the coherent output power (COP) method and spectral proper orthogonal decomposition. It is found that the averaged COP based on opposite-side microphone pairs provides the most reliable results for the inflow microphone measurements. Both approaches, i.e., the wall array and the inflow microphones, are validated against open-test-section measurements, demonstrating that closed test sections can yield acoustic spectra of comparable quality to anechoic facilities at large pitch angles, where blade-tip noise dominates.