As of today, the Wikipedia entry for the hummingbird explains that the bird's flight generates in its wake a single trail of vortices that helps the bird hover.
But after conducting experiments with hummingbirds in the lab, researchers at the University of California, Riverside propose that the hovering hummingbird instead produces two trails of vortices — one under each wing per stroke — that help generate the aerodynamic forces required for the bird to power and control its flight.
The results of the study could find wide application in aerospace technology and the development of unmanned vehicles for medical surveillance after natural disasters.
The researchers used high-speed image sequences — 500 frames per second — of hummingbirds hover-feeding within a white plume (emitted by the heating of dry ice) to study the vortex wake from multiple perspectives. They also used particle image velocimetry (PIV), a flow-measuring method used in fluid mechanics, to quantitatively analyze the flow around the hummingbirds. PIV allowed the researchers to record the particles surrounding the birds and extract velocity fields.
The films and velocity fields showed two distinct jets of downwards airflow — one under each wing of the hummingbird. They also revealed that vortex loops around each jet are shed during each upstroke and downstroke.
The researchers therefore propose in their paper published online last month in the journal Experiments in Fluids that the hummingbird's two wings form bilateral vortex loops during each wing stroke, which is advantageous for maneuverability.
"Previous studies have indicated that slow-flying bats and faster flying birds produced different structures in their wakes," said Douglas Altshuler, formerly an assistant professor of biology at UC Riverside, whose lab led the research. "We have been investigating the wake structure of hovering hummingbirds because this allows us to decouple the effects of different types of wings — bat versus bird — from different forward flight speeds.
Hummingbirds each weigh 2-20 grams. Because they can hover with high precision, they are able to drink nectar from flowers without any jiggling movement to their bodies. Besides using upstrokes and downstrokes, hummingbirds can rotate their wings. They can even flap their wings from front to back with a 180-degree amplitude.
"We began this study to investigate how the hummingbird used its tail while hovering," said Marko Princevac, an associate professor of mechanical engineering and a coauthor of the research paper. "After all, many insects also hover, but they have no tail. Instead, however, our research showed something interesting about the hummingbird's wings: the bilateral vortex structure. Hummingbirds hovering should cost a lot of energy but these birds are able to hover for long periods of time. Ideally, unmanned vehicles need to be operated with a very limited energy supply, which is why understanding how the hummingbird maximizes its use of energy is tremendously beneficial."
Sam Pournazeri, a former Ph.D. graduate student in Princevac's lab and a co-author on the paper, explained that in a downstroke, the air pressure difference developed as a result of wing movement creates flow from the bottom to the top of the wing. The result is a circular movement or vortex.
"Based on theories in fluid mechanics, this vortex should close either on the wing/body or create a loop around it," he said. "It's these loops that provide circulation around the wings and cause the hummingbird to overcome its weight. Hovering requires the bird to create a lift that cancels its body weight. Although the two-vortex structure we observed increases the hummingbird's energy consumption, it provides the bird a big advantage: a lot more maneuverability."
Next, the research team plans to study the hummingbird in a wind tunnel to closely observe how the bird transitions from hovering to forward motion, and vice versa.
"Current technology is not successfully mimicking how living things fly," Princevac said. "Drones don't hover, and must rely on forward motion. Research done using hummingbirds, like ours, can inform the development of the next generation of drones."
The research was funded by a grant from the National Science Foundation to Altshuler, now a faculty member at the University of British Columbia, Canada.
Paolo S. Segre, a former UCR graduate student working with Altshuler at the University of British Columbia, also participated in the study. Pournazeri and Segre contributed equally to the research.
The University of California, Riverside is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to Inland Southern California, the state and communities around the world. Reflecting California's diverse culture, UCR's enrollment has exceeded 21,000 students. The campus will open a medical school in 2013 and has reached the heart of the Coachella Valley by way of the UCR Palm Desert Center. The campus has an annual statewide economic impact of more than $1 billion. A broadcast studio with fiber cable to the AT&T Hollywood hub is available for live or taped interviews. UCR also has ISDN for radio interviews. To learn more, call (951) UCR-NEWS.
Iqbal Pittawala | EurekAlert!
Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY
NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
19.07.2018 | Earth Sciences
19.07.2018 | Power and Electrical Engineering
19.07.2018 | Materials Sciences