Natures wonders: aerodynamics of bird flocking (Introduction)

by David Turell , Saturday, April 27, 2024, 20:08 (12 days ago) @ David Turell

Definite principals are at play:

https://www.sciencedaily.com/releases/2024/04/240425131416.htm

"...you may very well see a flock of birds moving in unison as they migrate north. But how do these creatures fly in such a coordinated and seemingly effortless fashion?

"Part of the answer lies in precise, and previously unknown, aerodynamic interactions, reports a team of mathematicians in a newly published study. Its breakthrough broadens our understanding of wildlife, including fish, who move in schools.

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"The team's results show that the impact of aerodynamics depends on the size of the flying group -- benefiting small groups and disrupting large ones.

"'The aerodynamic interactions in small bird flocks help each member to hold a certain special position relative to their leading neighbor, but larger groups are disrupted by an effect that dislodges members from these positions and may cause collisions," notes Sophie Ramananarivo, an assistant professor.

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"The flows affected group organization in different ways -- depending on the size of the group.

"For small groups of up to about four flyers, the researchers discovered an effect by which each member gets help from the aerodynamic interactions in holding its position relative to its neighbors.

"'If a flyer is displaced from its position, the vortices or swirls of flow left by the leading neighbor help to push the follower back into place and hold it there," explains Ristroph, director of NYU's Applied Mathematics Laboratory, where the experiments were conducted. "This means the flyers can assemble into an orderly queue of regular spacing automatically and with no extra effort, since the physics does all the work.

"'For larger groups, however, these flow interactions cause later members to be jostled around and thrown out of position, typically causing a breakdown of the flock due to collisions among members. This means that the very long groups seen in some types of birds are not at all easy to form, and the later members likely have to constantly work to hold their positions and avoid crashing into their neighbors."

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"...they concluded that flow-mediated interactions between neighbors are, in effect, spring-like forces that hold each member in place -- just as if the cars of a train were connected by springs.

"However, these "springs" act in only one direction -- a lead bird can exert force on its follower, but not vice versa -- and this non-reciprocal interaction means that later members tend to resonate or oscillate wildly.

"'The oscillations look like waves that jiggle the members forwards and backwards and which travel down the group and increase in intensity, causing later members to crash together," explains Joel Newbolt,

***

"The team named these new types of waves "flonons," which is based on the similar concept of phonons that refer to vibrational waves in systems of masses linked by springs and which are used to model the motions of atoms or molecules in crystals or other materials."

Comment: There is no question the aerodynamic forces help all the birds in energy consumption to save energy for all. To help in visualizing the forces think of a racing car tucked up right behind another car, 'drafting', using the suction behind the first car to pull it along. It works the same in flocks.