The Physics of How Gentoo Penguins Can Swim So Fast Underwater – Ars Technica

Gentoo penguins They are the fastest swimming birds in the world, running at maximum underwater speeds of up to 36 km/h (about 22 mph). This is because their wings have evolved into flippers that are perfect for moving through water (albeit largely useless for flying through the air). Physicists have now used computational modeling of the hydrodynamics of penguin wings to gain additional insight into the forces and flows those wings create underwater. They concluded that the penguin’s ability to change the angle of its wings while swimming is the most important variable for generating thrust, according to The last paper Published in the Journal of Fluid Physics.

“Swimming penguins’ superior ability to start/brake, accelerate/decelerate, and turn quickly is due to their freely waving wings,” said co-author Prasert Prapamonthon from King Mongkut Ladkrabang Institute of Technology in Bangkok, Thailand. “They allow penguins to propel and maneuver in the water and maintain balance on land. Our research team has always been curious about evolved creatures in nature that would be beneficial to humankind.”

Scientists have always been interested in studying aquatic animals. Such research could lead to new designs that reduce the resistance of aircraft or helicopters. Or it could help build bio-inspired robots that are more efficient to explore and monitor underwater environments — such as Robocrilla small, one-legged, 3D-printed robot designed to mimic the movement of a leg krill So you can move smoothly in underwater environments.

Aquatic species have evolved in various ways to improve their efficiency while navigating through the water. For example, mako sharks can swim at speeds of 70 to 80 miles per hour, earning them the nickname “leopards of the ocean.” In 2019, scientists showed that a major factor in how mako sharks are able to move so quickly is the unique structure of their skin. They have small transparent scales, about 0.2 millimeters in size, called “teeth” throughout the body, especially concentrated in the wings and fins. The scales are more flexible in these areas compared to other areas such as the nose.

This has a profound effect on the degree of stress the mako shark experiences while swimming. It is caused by pull pressure flow separation around an object, such as an airplane or the body of a mako shark as it moves through the water. This is what happens when fluid flows away from the surface of the body, forming eddies and eddies that impede the body’s motion. The teeth can fold into the shark’s skin at angles of more than 40 degrees from its body – but only in a direction up against the flow (that is, from tail to nose). This controls the degree of flow separation, similar to dimples on a golf ball. Stippling, or scales in the case of the mako shark, helps maintain bound flow around the body, which reduces alert size.

Swamp grass shrimp increase forward propulsion thanks to the stiffness and increased surface area of ​​its leg. They also have two drag-reducing mechanisms: the legs are twice as flexible during the recovery stroke and bend more strongly, resulting in less direct interaction with the water and fewer wakes (smaller eddies); And instead of three legs moving separately, their legs basically move as one, which greatly reduces drag.

There have also been many studies examining the biomechanics, kinesiology, and flipper shape of penguins, among other factors. Prabamonthon et al. He specifically wanted to delve into the hydrodynamics of how a flapping wing generates forward thrust. According to the authors, aquatic animals typically use two basic mechanisms to generate thrust in the water. One is drag-based, like rowing, and is well suited for moving at low speeds. For higher speeds, they use a levitation-flutter-based mechanism, which has been shown to be more efficient at generating thrust.

On one level, penguin wings are essentially feathered wings of an airplane, only shorter and flatter like flippers or paddles, with short, bushy feathers that help trap air to reduce friction and turbulence. Penguins can also alter the angle of their wings (active wing feathers) to reduce resistance when they need to adjust their swimming posture, along with pitch and flutter. In fact, the penguin’s wing is quite geometrically complex, according to the authors. There is an internal part in which the distance between the leading (front) edge and the trailing (rear) edge increases farther from root; the midsection where the tip is approximately parallel to the space between wingtip and wingtip; and the outer part, where the trailing edge of the wing is concave.

The team studied films of penguins swimming, combined with analysis of two-dimensional motion from the side. This data helped them build a hydrodynamic model to simulate the complex forces and flows around the wings, incorporating variables such as amplitude, frequency, and direction of wing flap and feathers, as well as the velocity and viscosity of the fluid medium. They used the ratio of thrust speed to forward speed to model wing motion and added a new variable they call “thrust angle”, which is basically determined by the angle of attack and the angle of the wings relative to the forward direction.

Prabamonthon et al. concluded that penguins use a lift-based propulsion mechanism while swimming. Furthermore, the movement of the feathers is essentially how penguins produce such powerful forward thrust in the water. The optimal amplitude during gradation generates the greatest thrust. Penguins are obviously experts at finding that sweet spot.

However, if there is too much capacitance, it will cause negative impulse. When the wings flap, they produce vortices, most notably a Leading edge spiral (LEV) On the roof of the pavilion is a Prapamonthon et al. It is found to play an important role in generating both lift and thrust. “In the lower stroke, for example, introducing a vane angle weakens the intensity of the local exhaust ventilation on the upper deck (suction side) and reduces lift,” the authors write. “However, the excessive feathering angle shifts the undersurface to the suction side, resulting in a lower level of local exhaust ventilation near the root. This shift could explain the negative thrust caused by excessive vane widening.”

DOI: Physics of Fluids, 2023. 10.1063 / 5.0147776 (about DOIs).