Direct numerical simulation of acoustic reduction using serrated trailing-edge on an isolated airfoil

Abstract

Broadband noise produced by the trailing edge of a controlled diffusion (CD) airfoil with a serrated trailing edge in the actual anechoic wind-tunnel test configuration is directly simulated using a Lattice-Boltzmann method at a high Reynolds number of 1.5× 10 typical of actual ventilation systems and low pressure turbomachinery stages. Such an unique simulation resolves both the aerodynamic and acoustic field around the airfoil. The comparison of the airfoil loading, the wall-boundary layer development, and the near-wake flow between the clean and serrated configurations is systematically performed and results are compared with the detailed experimental database available for the clean airfoil. A slight lift reduction is found with the serrations near the trailing-edge. The turbulent wallpressure fluctuations on the airfoil suction-side are only slightly modified. Because of the serrations the pressure and suction side boundary layer flows merge differently than in the clean case, modifying the near-wake evolution with larger coherent hairpin structures. The slight vortex shedding observed on the pressure side of the clean airfoil is also suppressed. Finally a noise reduction is captured between 1000 and 3500 Hz in all direction except in the wake direction where a slight noise increase is noticed.