Flow Field of Flapping Albatross-like Wing and Sound Generation at Low Reynolds Number

Abstract

Both the unsteady flow and acoustic characteristics of the albatross-like flapping wing were numerically investigated. The flow around the flapping wing was predicted by using ANSYS Fluent^Ò unsteady three-dimensional compressible Navier-Stokes equations. The acoustic field was calculated by a built-in acoustic package, based on the FfowcsWilliams-Hawkings (FW-H) acoustic analogy. During the start-up motion, the large start-up vortices dominate the otherwise quiescent field with minimal sound generated. The sound is generated by the rotational and tangential motions of the wing using different sound generation mechanisms. A primary dipole tone at wing beat frequency is generated by the rotational motion, while other dipole tones at higher frequencies are produced by the vortex scattering at the trailing-edge of the wing during the tangential motion. The frequency composition of the primary tone changes with the pitching angle of the wing. During the steady flapping state, the quadruple sound is produced more due to the wake vortex interaction. The far-field sound spectrum is of broader bandwidth. The sound produced propagates only for short distance.