Navigation Links
Following the leader can be a drag, according to student's research on flapping flags
Date:11/7/2008

From the Tour de France to NASCAR, competitors and fans know that speed is only part of the equation. Strategy -- and the ability to use elements like aerodynamic drafting, which makes it easier to follow closely behind a leader than to be out in front -- is also critical.

But in some cases, drafting happens in reverse: It's the leader of a pack who experiences reduced drag, while the followers encounter more resistance -- and have to expend more energy to keep up.

In research published in the Nov. 7 issue of Physical Review Letters (Vol. 101: No. 194502), Cornell fourth-year physics graduate student Leif Ristroph and New York University researcher Jun Zhang used a simple tabletop experiment to show that two or more flexible objects in a flow -- flags flapping in the wind, for example -- experience drag very differently than rigid objects in a similar flow.

The findings could help biologists understand a variety of phenomena, including why animals like fish and birds travel in groups.

"It's counterintuitive," said Ristroph. "People who have studied schooling fish and flocking birds always postulate that they flock because the ones downstream can save energy, and the guy who's at the front has to work harder. Here's a case where that gets turned on its head."

To test the effects of a flowing fluid on flexible objects, Ristroph created a thin film of soapy water -- the beginning of a giant soap bubble -- stretched between two fishing lines and constantly refreshed with a flow of water from the top. Into the membrane, he inserted pieces of thin rubber (the flags) -- attached to perpendicular wire "flagpoles."

To measure the forces on the flags as water flowed past them, Ristroph attached small mirrors -- actually microscope cover slips -- to the far ends of the "flagpoles." As the flags flapped in the flow, the slightly flexible poles moved correspondingly -- and by shining a laser light on the mirrors, Ristroph could see the movements magnified and traced on a far wall.

He also used optical interferometry -- a technique based on the way light waves interfere with each other -- to measure the fluid flow around the flapping flags.

Instead of finding that the front flag took the brunt of the drag and following flags experienced less resistance, he found that for two flags close together, the front flag flapped less and thus experienced less drag -- even relative to a single flag without a follower. For the follower, he found the reverse: The flag oscillated more and experienced correspondingly more drag.

"That was completely unexpected," Ristroph said. Additional experiments with multiple flags and different spacing showed that the effect is consistent for closely spaced objects and drops off as the space between them increases.

The effects aren't fully understood, Ristroph said. "It appears that the follower is sort of confining the flow at the trailing edge of the leader, so it feels like he can't flap as hard; [and therefore] the amplitude of the leader is reduced." For the follower, the oscillations of the leader likely cause a resonating effect, increasing the follower's flapping and thus its drag.

"This is now like a two-way conversation, where the fluid talks to the object, and the object talks back," Ristroph said.

"Simulating this is very difficult," he added. "The theory and the simulation really cannot handle how to deal with the flow and an object that has flexibility.

"You often have to do the experiment," he said. "And when you do the experiment you can get something that is counterintuitive."


'/>"/>

Contact: Blaine Friedlander
bpf2@cornell.edu
607-254-8093
Cornell University Communications
Source:Eurekalert

Related biology news :

1. Researchers block damage to fetal brain following maternal alcohol consumption
2. Following traumatic brain injury, balanced nutrition saves lives
3. When following the leader can lead into the jaws of death
4. MNI researchers locate neurological basis of depression following sports concussion
5. Researchers take first steps towards spinal cord reconstruction following injury
6. LSU professor studies army-ant-following birds
7. Ecologist finds dire devastation of snake species following floods of 93, 95
8. Gender biases in leadership selection during competitions within and between groups
9. World leaders in infectious diseases convene to discuss emerging global viruses
10. Growing a garden of future environmental leaders
11. USGS Coalition to honor Reps. Dicks, Regula with Leadership Award
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:1/26/2017)... 26, 2017  Crossmatch, a leading provider of security ... aimed at combatting fraud, waste and abuse in assistance ... the Action on Disaster Relief conference in ... UN agencies and foreign assistance organizations throughout ... abuse are a largely unacknowledged problem in the foreign ...
(Date:1/24/2017)... 2017  It sounds simple and harmless—an electronic ... vital signs and alerts parents on their smart ... level drops. But pediatric experts argue that such ... no evidence of medical benefits, especially to healthy ... to parents of healthy babies, promising peace of ...
(Date:1/19/2017)... 2017 Sensory Inc ., a ... for consumer electronics, and i nnerCore ... cybersecurity solutions, today announced a global partnership that ... worldwide to bolster security of data sensitive mobile ... authentication platforms they offer, innerCore now offers its ...
Breaking Biology News(10 mins):
(Date:2/17/2017)... 17, 2017  If only one in every ... mutation-conferring resistance to chemotherapy, thousands of cancer cells ... focused on finding these mutations in ever-smaller subpopulations ... tumor DNA in blood — to guide treatment ... Unfortunately, however, detecting these genetic anomalies may ...
(Date:2/16/2017)... MI (PRWEB) , ... February 16, 2017 , ... Avomeen ... p.m. The event will be held at Avomeen Analytical Services (4840 Venture Dr., ... a MichBio member organization. They provide an opportunity to interact with peers, make new ...
(Date:2/16/2017)... Feb. 16, 2017  ArmaGen, Inc., a privately ... to treat severe neurological disorders, today reported preliminary ... AGT-181, the company,s investigational therapy for the treatment ... mucopolysaccharidosis type I, or MPS I). The initial ... study, presented today at the 13 th ...
(Date:2/16/2017)... February 16, 2017 Patient ... of innovative telemedicine application, new and leading edge ... experiencing a boom worldwide. The healthcare sector as ... technologies, services and new therapies for companies such ... RHT), Cellectar Biosciences, Inc. (NASDAQ: CLRB ...
Breaking Biology Technology: