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

Abstract

The humpback whale (Megaptera novaeangliae) is exceptional among the large baleen whales in its ability to undertake aquabatic maneuvers to catch prey. Humpback whales utilize extremely mobile, wing-like flippers for banking and turning. Large rounded tubercles along the leading edge of the flipper are morphological structures that are unique in nature. The tubercles on the leading edge act as passive-flow control devices that improve performance and maneuverability of the flipper. Experimental analysis of finite wing models has demonstrated that the presence of tubercles produces a delay in the angle of attack until stall, thereby increasing maximum lift and decreasing drag. Possible fluid-dynamic mechanisms for improved performance include delay of stall through generation of a vortex and modification of the boundary layer, and increase in effective span by reduction of both spanwise flow and strength of the tip vortex. The tubercles provide a bio-inspired design that has commercial viability for wing-like structures. Control of passive flow has the advantages of eliminating complex, costly, high-maintenance, and heavy control mechanisms, while improving performance for lifting bodies in air and water. The tubercles on the leading edge can be applied to the design of watercraft, aircraft, ventilation fans, and windmills.

Control of the separated flow around an airfoil using a wavy leading edge inspired by humpback whale flippers

“…This is related to the presence of the counter-rotating streamwise vortices which tend to accelerate the fluid in between them by adding momentum, and thus confer to the fluid the extra amount of kinetic energy necessary to prevent local separation. This analysis, obtained in a massively separated flow configuration, is in good agreement with the one proposed recently in [19] to explain the delay of stall angle observed in the presence of leading edge bumps.…”

“…In particular, the vorticity appears to roll up into a vortex tube which is initially vertical, and then immediately tilted into the streamwise direction, as it is advected by the mean stream. This Kelvin-Helmholtz-driven scenario suggests a completely different mechanism for the generation of the streamwise rollers than the "delta wing" one proposed by other authors [1,19] and is similar to conceptual models for the generation of quasi streamwise vortices from the destabilization of wall streaks in near wall turbulence [23].…”

“…Let us mention that in experimental studies at higher Reynolds numbers [6,1], PIV measurements show the trace of these streamwise rolls. Fish et al [19] suggest a similar scenario claiming that the pairs of counter-rotating vortices generated on each side of the bump are generated through a mechanism similar to the one observed on a delta wing.…”

Performance and mechanism of sinusoidal leading edge serrations for the reduction of turbulence–aerofoil interaction noise

“…The significance of these vortices in affecting aerodynamic behaviour was also observed by Stanway (2008) in PIV measurements of the flow in the vicinity of a serrated leading edge. A number of researchers (Fish & Lauder 2006;Fish et al 2011;Zhang et al 2013;Van Nierop et al 2008) have investigated the mechanism by which stall can be delayed by the introduction of serrations at the aerofoil leading edge. They observed that the LE serrations generate streamwise vortices, which were attributed to greatly enhanced momentum transfer.…”

Streamwise counter-rotating vortices generated by triangular leading edge pattern in flat plate boundary layer

“…The combination of large sinusoidal tubercles and the high aspect ratio of flippers on humpback whales leads to an increase of the lift to drag ratio and enables it to do sharp banking turns, and to be more maneuverable compared to other species in spite of its massive body (Fish and Battle 1995;Fish et al 2011). Wind tunnel experiments conducted by Miklosovich et al (2004) showed that the tubercles cause the flipper to have a greater stall angle and maximum lift coefficient.…”