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

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