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Regimes of tonal noise on an airfoil at moderate Reynolds number

Published online by Cambridge University Press:  04 September 2015

S. Pröbsting ,
F. Scarano  and
S. C. Morris
S. Pröbsting*
Affiliation:
Department of Aerodynamics, Wind Energy, Flight Performance, and Propulsion, Delft University of Technology, 2629 HS Delft, The Netherlands
F. Scarano
Affiliation:
Department of Aerodynamics, Wind Energy, Flight Performance, and Propulsion, Delft University of Technology, 2629 HS Delft, The Netherlands
S. C. Morris
Affiliation:
Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN 46556, USA
*
†Email address for correspondence: [email protected]
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Abstract

Tonal noise generated by airfoils at low to moderate Reynolds number is relevant for applications in, for example, small-scale wind turbines, fans and unmanned aerial vehicles. Coherent and convected vortical structures scattering at the trailing edge from the pressure or suction sides of the airfoil have been identified to be responsible for such tonal noise generation. Controversy remains on the respective significance of pressure- and suction-side events, along with their interaction for tonal noise generation. The present study surveys the regimes of tonal noise generation for low to moderate chord-based Reynolds number between $\mathit{Re}_{c}=0.3\times 10^{5}$ and $2.3\times 10^{5}$ and effective angle of attack between $0^{\circ }$ and $6.3^{\circ }$ for the NACA 0012 airfoil profile. Extensive acoustic measurements with smooth surface and with transition to turbulence forced by boundary layer tripping are presented. Results show that, at non-zero angle of attack, tonal noise generation is dominated by suction-side events at low Reynolds number and by pressure-side events at high Reynolds number. At smaller angle of attack, interaction between events on the two sides becomes increasingly important. Particle image velocimetry measurements complete the information on the flow field structure in the source region around the trailing edge. The influences of both angle of attack and Reynolds number on tonal noise generation are explained by changes in the mean flow topology, namely the presence and location of reverse flow regions on the two sides. Data gathered from experimental and numerical studies in the literature are reviewed and interpreted in view of the different regimes.

JFM classification

Acoustics: Aeroacoustics Boundary Layers: Boundary layer separation Vortex Flows: Vortex shedding
Type
Papers
Information
Journal of Fluid Mechanics , Volume 780 , 10 October 2015 , pp. 407 - 438
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Copyright
© 2015 Cambridge University Press 

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