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!
Navigational view of the brain thanks to powerful X-rays
18.10.2017 | Georgia Institute of Technology
Separating methane and CO2 will become more efficient
18.10.2017 | KU Leuven
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
17.10.2017 | Event News
10.10.2017 | Event News
10.10.2017 | Event News
18.10.2017 | Materials Sciences
18.10.2017 | Physics and Astronomy
18.10.2017 | Physics and Astronomy