Abstract
The interaction of a turbulent flow with the leading edge of a blade is a main noise source mechanism for fans and wind turbines. Motivated by the silent flight of owls, the present paper describes an experimental study performed to explore the noise-reducing effect of comb-like extensions, which are fixed to the leading edge of a low-speed airfoil. The measurements took place in an aeroacoustic wind tunnel using the microphone array technique, while the aerodynamic performance of the modified airfoils was captured simultaneously. It was found that the comb structures lead to a noise reduction at low frequencies, while the noise at high frequencies slightly increases. The most likely reasons for this frequency shift are that the teeth of the combs break up large incoming turbulent eddies into smaller ones or that they shift turbulent eddies away from the airfoil surface, thereby reducing pressure fluctuations acting on the airfoil. The aerodynamic performance does not change significantly.
Highlights
When turbulent eddies interact with the blade of a fan or a wind turbine, noise is generated at the leading edge
The present paper describes an experimental study of the noise generated by airfoils whose leading edges are modified using comb-like extensions, focusing on the noise generated by the interaction of the airfoil leading edge with turbulence in the incoming flow
The aerodynamic performance of the airfoils modified with different leading-edge comb structures will be compared
Summary
When turbulent eddies interact with the blade of a fan or a wind turbine, noise is generated at the leading edge. Experimental studies on the reduction of turbulence interaction noise mainly focus on modifying the blade geometry This can be done by using serrated edges, as for example examined by Soderman [1], Hersh et al [2], Gruber et al [3], Roger et al [4], Liu et al [5], Narayanan et al [6] and Juknevicius and Chong [7]. These include serrated and wavy leading edges [19,20,21,22,23,24,25,26,27] as well as porous materials [28,29] Another recent numerical study was performed on the potential noise reduction of a blade with a leading-edge modified with hooks [30].
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