Meeting Abstract
The mechanisms associated with the owls’ silent flight have been an active scientific research for decades as an inspiration to find solutions for noise reduction applications. Aerodynamic noise generated during flight is associated with the fluid-structure interaction phenomena and the turbulent nature of the flow. When turbulent airflow past the owl wing it is constantly interfered with the wing. During flapping, this interaction results in a more complex three-dimensional unsteady wake. The formed wake is shed downstream and carries the history of the flow affected by the bird. The interaction between the turbulent wake and the wing motion governs the aerodynamic forces acting on the owl and attenuating the noise at the interface region. Understanding the downstream wake-flow dynamics of owl flight can possibly elucidate the aerodynamic mechanisms employed by owls during flight and provide insight to the reduction of the aeroacoustics noise. We focus on the role of turbulence as a noise source and its impact on the aerodynamic performances of owl during flapping flight. We chose three owl species: boobook owl, great horned owl and Tawney owl. The owls were freely flown in a climatic wind tunnel. The wake flow field was measured using long duration high-speed PIV and the owls’ kinematics were characterized using high-speed imaging, simultaneously. Large lift and drag variations over the wingbeat cycle were observed, demonstrating the unsteady effects of the flow on lift. The owls’ wakes were populated by relatively small turbulence scales. Turbulent energy budgets at the wake depicted high levels of dissipation compared to turbulent production. By estimating the vorticity-strain relations at the wake, we have calculated the pressure gradients at the wake which are proportional to the aerodynamic noise. These appeared to be suppressed, indicating a passive control mechanisms through turbulence dissipation.
