Effects of owl-inspired leading-edge serrations on tandem wing aeroacoustics

Leading-edge (LE) serrations on owls’ outermost remiges play a crucial role in the silent flight of owls. While the aeroacoustic characteristics of LE serrations have been widely studied using single feathers/airfoils, how they affect feather–feather (feather slots) interactions during flight remains unclear. Here, we present a numerical analysis of the effects of owl-inspired LE serrations on the aeroacoustics of tandem wing models. Large-eddy simulations and Ffowcs Williams–Hawkings analogy are combined to resolve the flow and acoustic fields around the tandem wings. The results demonstrate that serration-induced aeroacoustics are closely associated with the gap distance (D) between fore and hind wings. At a low AoA of 5°, as D increases, the LE serrations on the fore wing initially reduce the far-field sound pressures (D < 0.22c) by passively altering the laminar–turbulent transition on upper wing surfaces but turn out to increase the sound pressures remarkedly when D > 0.22c due to the flow instability induced at the hind wing LE. However, at a high AoA of 15°, the fore wing serrations enable robust sound reductions for all gap distances by mitigating the flow instabilities in the vicinity of the fore wing trailing edge and hind wing LE. Furthermore, the combination of LE serrations on fore and hind wings is verified to be capable of bringing nonlinear synergetic effects on the suppression of flow fluctuations and noise, which can inspire innovative biomimetic designs for low-noise multirotor drones and wind turbines.