Flow turning effect and laminar control by the 3D curvature of leading edge serrations from owl wing

TL;DR

This study introduces a novel laminar flow control mechanism inspired by owl wing feathers, demonstrating that 3D-curved leading edge serrations can turn boundary layer flow and delay transition, potentially reducing noise during flight.

Contribution

It presents a new bio-inspired design of leading edge serrations that effectively control flow turning and delay laminar-turbulent transition on swept wings.

Findings

Flow turning effect extends along the chord, counteracting cross-span flow.

Comb-induced velocity profiles match theoretical transition delay conditions.

The mechanism likely contributes to quieter owl flight.

Abstract

This work describes a novel mechanism of laminar flow control of a backward swept wing with a comb-like leading edge device. It is inspired by the leading-edge comb on owl feathers and the special design of its barbs, resembling a cascade of complex 3D-curved thin finlets. The details of the geometry of the barbs from an owl feather were used to design a generic model of the comb for experimental and numerical flow studies with the comb attached to the leading edge of a flat plate. Examination was carried out at different sweep angles, because life animal clearly show the backward sweep of the wing during gliding and flapping. The results demonstrate a flow turning effect in the boundary layer inboards, which extends along the chord over distances of multiples of the barb lengths. The inboard flow-turning effect described here, thus, counter-acts the outboard directed cross-span flow typically appearing for backward swept wings. From recent theoretical studies on a swept wing, such a way of turning the flow in the boundary layer is known to attenuate crossflow instabilities and delay transition. A comparison of the comb-induced cross-span velocity profiles with those proven to delay transition in theory shows excellent agreement, which supports the laminar flow control hypothesis. Thus, the observed effect is expected to delay transition in owl flight, contributing to a more silent flight