AeroFeathers: Feathered airfoils inspired by the quiet flight of owls

Abstract

Owls are well-known as the quietest flying birds. Recent studies show that they achieve noise-less flight because of their specialized feather design. Their feathers have three important components: a velvety surface texture, comb-like hooks on their leading edge, and jagged fibrous fringes on their trailing edges. Some researchers have attempted to imitate these design features within airfoil designs to reduce aeroacoustic noise emitted by fixed wing and vertical lift vehicles; however, such features cannot be easily fabricated using traditional manufacturing processes. In this student-led project funded by NASA’s University Student Research Challenge, we leverage our established success at additively manufacturing fibrous structures to introduce a new method to 3-D print velvety textures, fibrous fringes, and flexible edge serration using low-cost material extrusion-based printing methods. By altering the printer’s G-code, we create customized feathered airfoils with individual design parameters, including serration thickness and fringe density. We conduct acoustic tests in an anechoic chamber and aeroacoustic tests in an acoustic wind tunnel to determine the effect of each parameter on the overall acoustic signature of the airfoil. We analyze the data and explain the role of owl feather-like features on the noise reduction performance of propeller blades and scaled fixed-wing airfoils.