Owls are extraordinary predators that are able to suppress their aerodynamic noise generation and achieve effectively silent flight over a broad frequency range, which includes the sensitive hearing ranges of owls, their prey, and humans. The poroelastic fringe adaptation of owls is believed to contribute to this broadband noise suppression by modifying the trailing-edge noise mechanism that sets the minimum noise level of many engineering designs, such as computer fans, propulsors, commercial airframes, and wind turbines. Many applications for which weaker edge noise is sought are also constrained by, for example, aerodynamic performance or stability metrics related to the integrated pressure across these fluid-loaded structures (e.g., lift or moment). Furthermore, it is clear that changes to the trailing-edge geometry and compliance to improve acoustic performance should entail an aerodynamic performance penalty. In this scenario, the unsteady acoustic and hydrodynamic fields must be considered together. At present, guidance towards a more complete understanding of their interaction for finite-chord and finite-span structures with variable porous and elastic properties is lacking. Furthermore, there is little empirical support for the predicted aerodynamic and aeroacoustic effects of poroelastic edges. The principal aim of this project is to address these shortcomings through a series of analytical and numerical model problems coordinated with experimental measurement to elucidate the unsteady loading and noise generation of thin fluid-loaded structures with graded poroelastic properties.
This project addresses the above technical shortcomings through an interactive theoretical-experimental program that distinguishes itself in no fewer than three ways: (i) construction of analytical and numerical frameworks to predict turbulence noise generation by graded poroelastic structures, from first principles; (ii) experimental validation of acoustic scaling laws for poroelastic edges, without background flow noise; and (iii) development of a glider to measure wing noise on the fly in a manner consistent with how owls hear their self-noise. The modeling and validation efforts aim to transform a biologically-inspired noise solution into a rational paradigm for passive aerodynamic noise control in low-speed flows and to create an experimental platform for future bionic owl noise-reduction studies. This project will also include K-12 educational outreach with the DaVinci Science Center (Allentown, PA), as well as integrate undergraduate research involvement through the Lehigh Biosystems Dynamics Summer Institute (in partnership with Northampton Community College) and through a design-build-fly competition between Lehigh and Penn State.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
|Effective start/end date||6/15/18 → 5/31/22|
- National Science Foundation: $301,488.00