The effect of three dimensional geometry variations of saw-tooth trailing edge serrations on their noise emission

The potential to reduce aerofoil noise through the addition of trailing edge serrations was well documented and had found many technical applications. Most research in this area focused mainly on the planform of the serrations. This paper investigated the effect of three dimensional geometric features of saw-tooth serrations with a fixed theoretical planform on the emission of sound. The emitted sound pressure was evaluated experimentally in an aeroacoustic wind tunnel. It was shown that serrations with a blunt edge with sharp corners emitted significantly lower levels of sound pressure than serrations with rounded edges. Further, it was found that chamfers towards the trailing edge on the pressure side of the serration led to an increased emission of sound, while an identical chamfer on the suction side did not have a negative effect. These findings questioned the applicability of theoretical models that assume an infinitely thin serration on geometries that can be produced in practice.