Reduction of tip-leakage noise by using porosity

Abstract

Tip-leakage noise remains one of the least understood sources of noise in ducted rotors used in industry across different sectors including aerospace, automotive, and ventilation systems. Different technologies have been proposed to reduce tip leakage noise by treating either the duct casing over the tip rotor or the blade tip itself. This work describes an experimental investigation to assess the performance of blades with a porous tip treatment in reducing tip-leakage noise. The set-up consists of a static airfoil with its tip located over a flat plate and separated from the airfoil tip by a small gap. Synchronous measurements of the far-field noise and surface pressure fluctuations on the bottom plate have shown that the modification of the source near-field by the porous tip almost completely cancels the tip-leakage noise. One of the key findings is that treating only a small region close to the mid-chord of the aerofoil is enough to suppress the dominant tip noise sources. Measurements of the unsteady flow field close to the tip suggest that the porous tip reduces the intensity of the turbulence close to the aerofoil tip typically associated with the generation of tip-leakage noise.

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ORCID for Sergi Palleja Cabre: orcid.org/0000-0002-5414-7716

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