Flippers Provide Lift, Reduce Drag

a humpback whale breeches above water, its underbelly to the sky and barnacles can be seen on its stomach and flippers

Biological Strategy

Humpback whale

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Water is not only the most abundant liquid on earth, but it’s vital to life–so it’s no surprise that the majority of life has evolved to thrive on and under its surface. Moving efficiently in and on this dense and dynamic substance presents unique challenges and opportunities for living systems. As a result, they have evolved countless solutions to optimize drag, utilize surface tension, fine tune buoyancy, and take advantage of various types of currents and fluid dynamics. For example, sharks can slide through water by reducing drag due to their streamlined shape and specially shaped features on their skin.

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Class Mammalia (“breast”): Bats, cats, whales, horses, humans

Mammals make up less than 1% of all animals on earth, but they include some of the most well-known species. We know first-hand some of the characteristics that make mammals unique, like having hair, being able to sweat, and producing milk through mammary glands. Another critical shared feature is a set of highly-specialized teeth. Unlike sharks or alligators, for example, whose teeth are generally all the same size and shape, mammals have differently shaped teeth in different areas of the jaws to target specific foods or foraging strategies.

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The flippers of the humpback whale channel flow and increase aerodynamic efficiency due to tubercles or bumps.

Flippers on humpback whales (Megaptera novaeangliae) have non-smooth leading edges, yet demonstrate superior fluid dynamics to the characteristically smooth leading edges of our wings, turbines and other kinds of blades. Despite being 40-50 feet long and weighing nearly 80,000 pounds, humpback whales swim in circles tight enough to produce nets of bubbles only five feet across, which corral their shrimp-like prey.

The whale’s surprising dexterity is due primarily to its non-conventional flippers, which have large, irregular looking bumps called tubercles across their leading edges. Whereas sheets of water flowing over smooth flippers break up into myriad turbulent vortices as they cross the flipper, sheets of water passing between a humpback’s tubercles maintain even channels of fast-moving water, allowing humpbacks to keep their “grip” on the water at sharper angles and turn tighter corners, even at low speeds.

side view of a humpback whale with white lines tracing the path of water over the flipper

Wind tunnel tests of model humpback flippers with and without leading-edge tubercles have demonstrated the fluid dynamic improvements tubercles make, such as a staggering 32% reduction in drag, 8% improvement in lift, and a 40% increase in angle of attack over smooth flippers before stalling. A company called WhalePower is applying these lessons to the design of wind turbines and fans of all sorts – industrial ceiling fans and other HVAC systems, computer fans, etc. – to improve their efficiency, safety, and cost-effectiveness.

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Last Updated September 14, 2016

References

“The humpback whale (Megaptera novaeangliae) is reported to use its elongate pectoral flippers during swimming maneuvers. The morphology of the flipper from a 9.02-m whale was evaluated with regard to this hydrodynamic function. The flipper had a wing-like, high aspect ratio plan- form. Rounded tubercles were regularly interspersed along the flipper’s leading edge. The flipper was cut into 71 2.5-cm cross-sections and photographed. Except for sections near the distal tip, flipper sections were symmetrical with no camber. Flipper sections had a blunt, rounded leading edge and a highly tapered trailing edge. Placement of the maximum thickness placement for each cross-section varied from 49% of chord at the tip to 19% at mid-span. Section thickness ratio averaged 0.23 with a range of 0.20-0.28. The humpback whale flipper had a cross-sectional design typical of manufactured aerodynamic foils for lift generation. The morphology and placement of leading edge tubercles suggest that they function as enhanced lift devices to control flow over the flipper and maintain lift at high angles of attack. The morphology of the humpback whale flipper suggests that it is adapted for high maneuverability associated with the whale’s unique feeding behavior.” (Fish and Battle 1995:51)

Journal article

Hydrodynamic design of the humpback whale flipper

Journal of Morphology | 24/02/2005 | Franke E. Fish, Juliann M. Battle

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Reference

“The humpback whale Megaptera novaeangliae is exceptional among the baleen whales in its ability to undertake acrobatic underwater maneuvers to catch prey. In order to execute these banking and turning maneuvers, humpback whales utilize extremely mobile flippers. The humpback whale flipper is unique because of the presence of large protuberances or tubercles located on the leading edge which gives this surface a scalloped appearance. We show, through wind tunnel measurements, that the addition of leading-edge tubercles to a scale model of an idealized humpback whale flipper delays the stall angle by approximately 40%, while increasing lift and decreasing drag.” (Miklosovic et al. 2004:L39)

Journal article

Leading-edge tubercles delay stall on humpback whale (Megaptera novaeangliae) flippers

Physics of Fluids | 16/03/2004 | D. S. Miklosovic, M. M. Murray, L. E. Howle, F. E. Fish

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Reference

Journal article

The Tubercles on Humpback Whales' Flippers: Application of Bio-Inspired Technology

Integrative and Comparative Biology | 17/05/2011 | F. E. Fish, P. W. Weber, M. M. Murray, L. E. Howle

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