Flow topology and noise emission around straight, serrated and slitted trailing edges using the lattice Boltzmann methodology

Abstract

The current study analyzes the flow topology and acoustic emission around straight, sawtooth serrated and slitted-sawtooth serrated trailing edges using a NACA0018 airfoil at zero degree angle of attack. By using this specific setup, pressure differences between both airfoil sides are avoided so that the focus will purely lie on the mean and fluctuating velocity. The flow field is analyzed by evaluating the fully explicit, transient, compressible Lattice Boltzmann equation. Acoustic perturbations are directly obtained from the computational measurement domain, as well as by means of a Ffowcs Williams and Hawking and Curle integral solution. Noise reductions up to 6 dB are achieved for the sawtooth serrated edge in comparison with the straight trailing edge case, while the slitted-sawtooth edge reaches a maximum of only 5 dB. At low frequencies, the solid-sawtooths outperform the slitted-sawtooths. The general trend in term of velocity results shows favorable streamwise, wall-normal and spanwise quantities for the slitted-sawtooth design, while the solid-sawtooth design shows less fluctuations in both streamwise, wall-normal and spanwise direction. Especially the increase of local, wall-normal fluctuations over the slitted-sawtooth serrated edge, enchances the generation of acoustic pressure waves, making it a less effective trailing edge noise-suppression add-on.