Turbulence Characteristics of Finlet Treatments Applied for Trailing Edge Noise Reduction of a NACA 0012 Airfoil

This study experimentally investigates the near-field flow characteristics associated with the capability for trailing edge noise reduction of a selected finlet surface treatment applied on a NACA 0012 airfoil. It continues from a previous study, in which a variation of finlet parameters was examined in order to establish a configuration optimal for trailing edge noise reduction. To identify the features of the turbulent boundary layer that are directly related to the reduction of far-field noise, the development of the turbulence in the boundary layer within and around the area treated with the finlets is analyzed and compared with the results for the untreated airfoil. The results for the velocity auto-correlation and the cross-correlation of pressure and velocity are examined to substantiate results from the static surface pressure, unsteady surface pressure fluctuations and boundary layer velocity along the airfoil chord and in particular within the treated area. Upon further analysis of the pressure and velocity fields, it is demonstrated how the noise emission is reduced due to the decreased level of small-scale turbulence convected past the sharp trailing edge along the airfoil surface. The reduction is found to be likely the effect of an interaction between the flow channeled through the finlet treatment and coherent structures further away from the airfoil surface occurring at the trailing edge, but also surface friction along the finlet wall-structures.