Numerical investigation of airfoil self-noise reduction by addition of trailing edge serrations

DNS of the flow around a NACA-0012 airfoil are conducted, employing an immersedboundary method to represent flat-plate trailing-edge extensions both with and withoutserrations. Properties of the turbulent boundary layer convecting over the trailing-edgeare similar for all cases. For cases with serrations, the trailing-edge noise produced by theflow over the airfoil is observed to decrease in amplitude, and the frequency interval overwhich the noise reduction occurs differs depending on the serration length. The trailing-edge noise appears otherwise largely unaffected by the serrations in terms of its directivityand spanwise coherence. The hydrodynamic behaviour in the vicinity of the trailing-edgeextensions is investigated. The streamwise discontinuity imparted upon the turbulent flowby the straight trailing-edge can clearly be observed in statistical quantities, whereas forthe serrated case no spanwise-homogeneous discontinuities are observed. The turbulentflow through the serrations promotes the development of horshoe vortices originating atthe serrations themselves, which appear to promote a more rapid mixing within the airfoilwake