What is it about?
The vortex that forms on top of the flapping wings is called leading-edge vortex (LEV) and it provides extra boost to its aerodynamic force. It turns out, there is a limit to how much the vortex can grow. Many biological organisms (insects, birds, and bats) flap their wings up until the vortex grows to that limit.
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Why is it important?
The limit on the growth of the leading-edge vortex suggests that the flapping frequency of insects, birds, and bats is governed by this intrinsic constraint. This finding is also consistent with the limit on the vortex ring growth observed in jet-propelling organisms such as jellyfish and dragonfly larvae, bringing us a step closer to a unifying principle of locomotion from the vortex formation point of view.
Perspectives
The part of the paper that we are most proud of is the "water bottle analogy." Often times, fluid mechanics (the physics of how fluids flow) papers are difficult to understand due to heavy math. However, the core physics that guided our mathematical derivation can be explained using a simple analogy. The intrinsic growth limit of the vortex bubble is akin to the limited size of the water bottle. As the small "swirlies" (known as vorticity) add to the vortex bubble, there is a point at which it can no longer accept more "swirlies," much like how a water bottle will overflow at some point. We hope this analogy help communicate to the readers the physical intuition that guided our discovery!
chris roh
Cornell University
Read the Original
This page is a summary of: Universal vortex formation time of flapping flight, Proceedings of the National Academy of Sciences, August 2025, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2501511122.
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