关键词: Three-dimensional trailing-edge fringes , · Aeroacoustics , · Large-eddy simulation , · Ffowcs Williams? Hawkings equation

Abstract: Owls are widely known for their silent flight, which is attributed to their unique wing morphologies comprising leading-edge (LE) serrations, trailing-edge (TE) fringes, and a velvety surface. The aeroacoustic characteristics of owl-inspired TE fringes have been widely investigated through two-dimensional (2D) modeling, but remain yet poorly studied in association with their three-dimensional (3D) effects. Here, we present a numerical study of the 3D aeroacoustic characteristics of owl-inspired TE fringes in which we combined large-eddy simulations (LES) with the Ffowcs Williams?Hawkings analogy. We constructed a clean wing model and three wing models with TE fringes that were distributed differently spanwise. The aerodynamic forces and 3D acoustic characteristics reveal that, like the 2D results of our previous studies, the 3D TE fringes enable remarkable sound reduction spatially while having aerodynamic performance comparable to the clean model. Visualizations of the near-field 3D flow structures, vortex dynamics, and flow fluctuations show that TE fringes can robustly alter the 3D flow by breaking 3D TE vortices into small eddies and mitigating 3D flow fluctuations. Particularly, it is verified that TE fringes alter spanwise flows, thus dominating the 3D aeroacoustic characteristics in terms of passive flow control and flow stabilizations, whereas the fringes are inefficient in suppressing the acoustic sources induced by wingtip vortices. Moreover, the TE fringes distributed at midspan have better acoustic performance than those in the vicinity of the wingtip, indicating the importance of a spanwise distribution in enhancing aeroacoustic performance.

Key words: Three-dimensional trailing-edge fringes , · Aeroacoustics , · Large-eddy simulation , · Ffowcs Williams? Hawkings equation