Results of a Wind Tunnel Study on the Reduction of Airfoil Self-Noise by the211 Application of Serrated Blade Trailing Edges

摘要

Wind tunnel measurements on the self-noise of a series of airfoils and flat211u001eplates were performed to explore the previously reported noise reducing potential 211u001eof serrated trailing edges in case of more realistic flows and geometries. For 211u001ethis purpose, different types of airfoils, and flat plates with varying planforms 211u001eand orientations of the teeth at the trailing edge were used. All serrated 211u001eairfoils yield reduced trailing-edge noise levels, the reduction ranging from 3 211u001edB up to 8 dB. Spectral shape and dependency on the flow speed and angle-of-211u001eattack appeared to be different for every airfoil type. The serrated flat plates 211u001ewere found to give reductions up to 10 dB (1 kHz-6 kHz). Inclination of the 211u001ecomplete flat plate by 10 degrees or a swept trailing edge affected this 211u001ereduction to a very limited extend only (<2 dB). The same holds for a 10 degrees 211u001emisalignment of the teeth with respect to the flow direction but in the chord 211u001eplane. However, misalignment of the teeth by 15 degrees with respect to the chord 211u001eplane caused an increase of the radiated noise.