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Understanding the Flapping Wing

Posted on August 2nd, 2011

Birds Gotta Fly, but How?

The wake of an oscillating fin revealed using dye visualization.

The wake of an oscillating fin revealed using dye visualization.

Who hasn’t marveled at a bird’s ability to stay on course through a wind storm, or a bee’s capacity to accurately zero in on a particular flower? IIHR Assistant Research Engineer James Buchholz recently won a research grant from the U.S. Air Force to unravel the laws of physics that govern the flow patterns and forces that birds and insects create as they flap their wings to move through the air. Buchholz’s 2011 Young Investigator Award from the Air Force Office of Scientific Research will provide $360,000 over three years for research to study these forces.

Buchholz, who is also an assistant professor of mechanical and industrial engineering at The University of Iowa, is the study’s principal investigator. Titled “Fundamental Bounds on Vortex Shedding in Forward Flapping Flight,” the research is designed to study the nature of the vortex-shedding events that help birds and insects maintain stability, perform articulate maneuvers, and control their trajectories even under turbulent conditions. An understanding of flapping flight could improve the performance of micro air vehicles (MAVs) inspired by birds and insects. These vehicles could potentially operate in complex settings, such as gusty urban street canyons.

Buchholz says he and his colleagues have discovered robust characteristics in the flow field around a low-aspect-ratio model of a fish fin. His research group at The University of Iowa plans to further explore and quantify these characteristics with regards to the aerodynamics surrounding a flapping wing. “As a wing or fin oscillates,” Buchholz says, “it sheds a highly complex, three-dimensional, and unsteady system of interconnected vortices. By studying these vortex structures, we hope to develop scaling laws that can help us predict how the vorticity is distributed in the wake. If we can do this accurately under varying conditions, the physical insight this will yield would go a long way toward developing better aerodynamic models for flapping wings and fins.”

Buchholz plans to develop an experimental platform that can produce the highly articulated movements of a flapping wing, along with methods and equipment to measure the aerodynamic forces and pressures at work, with the eventual goal of creating a mathematical model to accurately predict aerodynamic loads in flapping flight.

Buchholz is one of 43 scientists and engineers nationwide to receive a 2011 Young Investigator Award from the U.S. Air Force.

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