Hummingbirds can hover so well they seem to float in mid-air. With the help of a supercomputer, Vanderbilt University mechanical engineer Haoxiang Luo has fleshed out some of the secrets of how hummingbirds hover, flight that’s more similar to that of an insect than the typical bird. Luo and his colleagues published their results in the Journal of the Royal Society Interface. They hope this research can be used to help develop both micro and unmanned aerial vehicles.
Luo performed computer simulations of the three-dimensional flow patterns that swirl around a hummingbird’s wings using the Lonestar supercomputer of the Texas Advanced Computing Center. The Lonestar system is part of the National Science Foundation’s Extreme Science and Engineering Discovery Environment (XSEDE), a single virtual system that scientists use to interactively share computing resources, data and expertise.
“We used TACC’s Lonestar for both its CPU time and data storage,” said Luo. “The excellent computing power allowed us to complete the simulations in a reasonable amount of time.”
It’s easy enough to see that when a hummingbird hovers, the vertical force from its wings equals its body weight. However, understanding goes out the window when one looks more closely.
“The instantaneous force characteristics were previously unknown,” said Luo. “So was the three-dimensional flow stirred up by the bird. We are the first group to be able to directly quantify the time-varying forces within a stroke cycle.”
That force data is allowing scientists to grasp the connections between wing motion, the force produced by that motion, and the power consumed in beating their wings
As part of the experiment, a high-speed camera recorded at 1000 frames per second the flight of a trained female ruby-throated hummingbird that weighed a little less than a nickel coin. Dots of non-toxic white paint were brushed on the leading and trailing edge of its wings. A custom MATLAB program tracked the frame-by-frame motion of the dots and plotted their location in space.
According to Luo, the computational challenges were daunting in simulating the instant-by-instant full-body simulation of a hummingbird’s hover. “For a hummingbird with only a 10 centimeter wingspan, the unsteady aerodynamics is complex enough to require millions of mesh points to resolve the many, many small vortices stirred up by the wings — the bird essentially is flying in an ‘ocean of vortices.’ Therefore, efficient algorithms and high-performance computing are necessary for this work,” said Luo.
One of the interesting results from the study showed that most of the work done during a hover is on the wing’s downstroke, or forward stroke since the wings go back and forth while hovering. That’s even though the bird reverses its wings during the upstroke and sweeps them in a similar way as in the downstroke.
“This work will lead to better understanding of aerodynamics of flapping wings in nature and will be useful for development of UAVs and MAVs,” said Luo. “Biologists are also interested in the biomechanics of hummingbirds since they are a special species of birds and they are interested in it from an evolutionary point of view.”
For hummingbird fans, watching them dart off is as fun as watching them hover. Luo said he’ll study the stunt flying of hummingbirds in the next step of his research.
“We will study the coupling of unsteady aerodynamics of the hummingbird wings with its flight dynamics to understand how the bird performs maneuvers — essentially all kinds of aerial stunts they can do, such as a rapid turn.”
Read more in Wired: http://www.wired.com/2014/07/science-graphic-hummingbird-wings