Application of Finlets for Trailing Edge Noise Reduction of a NACA 0012 Airfoil

The present experiments investigate the reduction of trailing edge noise of a symmetric NACA 0012 airfoil using surface treatments, known as finlets. Treatment effectiveness is measured with observations from far-field data. Moreover, the highly instrumented airfoil model allows measurements of both static and dynamic surface pressure at various chord- and spanwise locations. In particular, measurements were carried out in between of the finlets, in order to elucidate clearly the near-field dynamics. With this, key parameters associated with trailing edge noise reduction could be identified. Relevant factors are, for instance, the spacing and the height of the finlets, as well as their relative positions with reference to the trailing edge. The results suggest that there possibly exists a strong correlation between the finlet height and the boundary layer thickness at the trailing edge. Attempting to identify different noise reduction mechanisms described in the previous studies, it was concluded that the prevailing one for airfoils is likely to be the detachment of small-scale turbulence structures from the airfoil surface. From the results of a position study it was inferred that shifting a treatment upstream from the airfoil trailing edge leads to beneficial effects in terms of trailing edge noise reduction compared to the configuration with the treatment applied flush with the trailing edge.