Flow Field Analysis and Contour Detection of a Natural Owl Wing Using PIV Measurements

Abstract

A technical three-dimensional wing model based on the geometry of the wing of a barn owl was designed to investigate the aerodynamic characteristics of this wing, which is known to be perfectly adapted to the requirements of silent flight. This wing model possesses the basic geometry of the barn owl wing. To understand the impact of the owl-based shape plus the owl-specific anatomic elements on the flow field and to further analyze the characteristic flow field that enables the owl to fly at low speeds and thus silently, a prepared natural owl wing was investigated in a wind tunnel. Measurements using particle-image velocimetry were performed on the model and on the natural wing to investigate characteristic flow phenomena such as separation, transition, and reattachment. Additionally, changes of the geometry, i.e., the maximum chord line-to-upper surface distance normalized by the chord length and the deflection of the natural owl wing, are described and discussed in detail to understand the resulting fluid-structure interaction. Unlike the rigid model, the natural owl wing possesses a high flexibility leading to a mutual influence of the wing structure and the surrounding flow field. This has to be investigated to understand the complex physical mechanisms that allow the highly efficient flight of the owl.