An experimental investigation of novel trailing edge geometries on airfoil trailing edge noise reduction

This paper presents a panel of trailing edge geometries for reducing airfoil trailing edge noise experimentally. Three serrated-type trailing edges were designed and are presented as a passive treatment to reduce broadband trailing edge noise on an isolated airfoil. These are the slits, sawtooth with holes and slitted sawtooth. A random trailing edge geometry aimed at reducing the scattering efficiency at the trailing edge is also presented. The noise performance is assessed for each treatment relative to a reference baseline straight edge. Results are also compared to a sawtooth serration of dimensions λ=h = 0:3, which was shown to provide significant noise reduction with minimal aerodynamic impact by Gruber [2012]. All trailing edge treatments are manufactured from stiff cardboard of 0:8mm thickness using a laser and inserted into the blunt slotted trailing edge of a NACA65(12)-10 airfoil (see Gruber [2012]). It is shown that broadband noise reductions of up to 5dB are obtained using the slitted sawtooth and up to 3dB with the random TE distribution. More importantly, it is shown that the expected high frequency noise increase normally observed with sawtooth serrations is reduced to null with these two trailing edges. No significant changes to the steady pressure are expected from the measured data (see static distribution along the sawtooth serrated airfoil in Gruber et al. [2010], Gruber [2012]). These innovative trailing edge treatments could be directly applied to low speed fans, such as wind turbine blades. The experimental results presented in this paper complement the analytical study shown by Azarpeyvand M. [2013].