On a three-dimensional investigation of airfoil turbulence-impingement noise and its reduction by leading-edge tubercles

• Published in: Journal of sound and vibration 2022-03, Vol.520, p.116635, Article 116635
• Main Authors: Bampanis, Georgios, Roger, Michel, Moreau, Stéphane
• Format: Article
• Language: English
• Subjects: Aeroacoustic propagation; Airfoil noise; Airfoils; Engineering Sciences; Fluids mechanics; Frequency ranges; Impingement; Leading edges; Mathematical models; Mechanics; Noise; Noise mitigation; Nozzles; Prediction models; Shear layers; Three dimensional models; Turbines; Turbulence; Wind tunnels
• ISSN: 0022-460X; 1095-8568
• DOI: 10.1016/j.jsv.2021.116635

The present work addresses the turbulence-impingement noise of an airfoil and its reduction by a wavy cut of the leading edge, referred to as serrations or tubercles. It is primarily aimed at completing existing experimental databases for both straight-edge and serrated airfoils, by measurements also performed off the mid-span plane on a portion of sphere, in an open-jet anechoic wind tunnel. The three-dimensional investigation is a required condition for further applications in rotating-blade noise modeling. The turbulence is generated by a grid placed upstream of the nozzle contraction. An almost monotonically increasing reduction is found with increasing frequency, in a wide frequency range for which turbulence-impingement noise dominates, for all radiation directions. This extends observations reported in previous studies in the midspan plane only. The straight-edge results are also used to validate an analytical prediction model in a three-dimensional context. This part includes a novel correction method to account for sound refraction through the shear layers of the nozzle jet, leading to a remarkably good agreement of predictions with measurements even at shallow observer angles where the effect of the jet shear layers is significant and needs to be accounted for. •Three-dimensional directivity of airfoil turbulence-impingement noise.•Sound emissions off the mid-span plane for straight-edge and serrated airfoils.•Monotonically increasing noise reduction with tubercles at all radiation directions.•Validation of Amiet’s analytical prediction model in a three-dimensional context.•Original sound refraction correction through the shear layers of the nozzle jet.