An experimental investigation of turbulent bounmdary-layer interaction with different serrated training-edge configurations

The paper presents an experimental investigation of a turbulent boundary-layer interaction over a
single large triangular serration at the Trailing-Edge (TE) of an airfoil on the flow-induced noise.
Experiments were conducted at low-to-moderate Reynolds number given by 1.8 105 < Rec < 5.7
105, where c is the chord of airfoil. Six different TE serration geometries were studied: Three
serrations with a single large triangular geometry at the TE, two serrations with varying orientation
relative to the airfoil, and a straight-edged reference plate (in which the TE triangular serration is not
considered). The airfoils with different TE configurations were placed in an anechoic wind tunnel in a
mean flow field with free-stream velocities of 25, 30 and 35ms1. The radiated acoustic pressure field
was recorded using a spiral microphone array located in the far-field. It was found that a significant
noise reduction up to 6 dB was obtained when the included angle of the triangular serration was less
than 45 ,which was in agreement with Howe’s theory. The Conventional Beamforming (CB) source
maps confirmed that the noise reduction was obtained by varying the included angle of the triangular
serrations. It was observed that the maximum noise attenuation occurred at frequencies above 5 kHz,
where the TE noise dominates over the Leading-Edge (LE) noise. For frequencies below 5 kHz, the LE
noise sources dominate over the TE noise.