Meeting Abstract
Owls are an order of birds where many species have developed a silent flight. The silent flight is achieved by several wing and feather adaptations, including serrations at the leading edge of the primary feathers which are exposed to the incoming airflow. Serrations are supposed to interact with the airflow and reduce flow separation. Many studies on serrations have been done with artificial serrated leading edges, yet these leading edges do not represent the three-dimensional shape of natural serrations. In this study we constructed a three dimensional model of an array of serrations on a barn owl (Tyto furcata pratincola) feather. Enlarged acrylic plastic models were fabricated from this template by 3D-printing and investigated in a water flow channel at Reynolds numbers equivalent to an owl flight velocity of 7.5 m/s. We investigated the model in laminar flow as well as in a vortex street that was created by a half-cylinder placed in front of the model by using Particle Image Velocimetry (PIV) to describe the effects of the serrations on the flow. Our results support previous studies on serrated leading edges that the serrations of owls help stabilizing the incoming flow by creating small-scale turbulences behind the leading edge that dissipate downstream. Unsteady flow is attenuated after impinging the serrations which is demonstrated by a lower RMS-value of the flow velocity parallel and normal to the bulk flow direction downstream of the serrations. We did not find such effects in free stream flow conditions or at a leading edge model with missing serrations that was used for comparison. We conclude that the serrations that can be found in owls help stabilize the incoming air flow in steady and unsteady flow conditions, which can provide flow control, especially during critical flight maneuvers like changing angles of attack and sweep angles of a moving wing.
