Enhancing the noise reduction capability of serrations using low-profile vortex generators

This paper presents an experimental investigation on improving the noise reduction capability of trailing edge serrations using upstream vortex generators. Experiments were conducted for a 100 mm chord NACA 0012 airfoil at four angle of attack between 0^◦ and 9^◦ and flow speed ranging from 20 to 50 m/s. The Reynolds number based on the chord length ranges from 1.3 × 10⁵ to 3.3 × 10⁵. Vane type vortex generators with various heights of h/δ = 0.125 − 0.25 were placed along with the serration roots, where δ is the boundary layer thickness at the trailing edge without the vortex generators. The aeroacoustic measurements were made with a phased microphone array, and the aerodynamic measurements near the trailing edge were measured using a hot wire. The source integrated noise spectra showed on average 2 dB reduction in the trailing edge noise over high frequency range above 3 kHz. The generation of streamwise vortices by vortex generators can be identified in the wake measurement. These streamwise vortices were further found to counteract the cross-flow generated at the serration roots, hence improving the performance of the serration.