No. 2935: WHALE AERODYNAMICS
by John H. Lienhard
Today whale aerodynamics. The University of Houston's College of Engineering presents this series about the machines
that make our civilization run and about the people whose ingenuity created them.
We've all seen movies of humpback whales playing in the sea.
The most obvious feature is a nice symmetrical tail slapping the water as it dives.
But we also see an awkward-looking flipper emerging as it breaches the water.
That flipper fin has white lumps along its edge - lumps called tubercles.
A Humpback Whale breaching and displaying the tubercles on the leading edge of its left fin. (Image courtesy of Wikipedia Commons)
You might even have noticed a Pacific Life Insurance ad
that ends as a humpback whale leaps out of the water, and that lumpy fin freezes into
its logo. That flipper fin seems so crudely made. But it's not what it seems. It's
actually a highly mobile wing that gives the whale fine control of its movement
So think how wings work: Most of us have, sometime, reached our hand out of a moving
car's window, palm slanted toward the wind, and felt it lift like an airfoil. At a zero
angle of attack (or zero tilt) our hand knifes through the air, feeling no lift and little
drag. Increase the angle and lift pulls our hand up while drag pushes it back. Those
forces increase with the angle. But let the angle of attack be great enough and our hand
suddenly jerks back - no more lift and a huge increase in drag. We call that the stall
angle. That's because air moving over the top suddenly detaches, leaving a large vacuum.
An airfoil whose angle of attack causes it to stall. (Image courtesy of Wikimedia Commons)
When an airplane reaches that point, the wing stops lifting it. Instead, it drags the airplane
to a halt. It stalls, then falls. Airplane designers have tried many ways to slow the onset of
stall - to make it more progressive, less sudden. We've looked out airplane windows and noticed
all kinds of gadgets on their wings - rows of little vertical plates, for example.
Now we find that the humpback whale might have the best gadget of them all. You see, the flow
of air is similar to the flow of water. A whale moves in water much as an airplane moves much
faster in air. Evenly spaced tubercles channel water (or air) back across the flipper (or wing)
in vortices. And either water or air clings longer to the fin (or to the wing) as the angle of
attack increases. That action is complex. But as engineers write the equations and do computer
simulations, they also make new products - wind turbine blades with bumpy leading edges, bumpy
fins reaching down from below fancy surfboards.
A tubercle-enhanced wind turbine blade built and photographed by Joe Subirona, by permission
of WhalePower Corporation. Note that the tubercles have been greatly enhanced in this design.
At this writing, I've yet to see them on a jet wing. But, if you hear this episode in a rerun,
you might have. And I think of how early airplane makers looked at birds and saw all the wrong
things. They saw flapping wings, but missed the fine control of feathers. Our theoretical knowledge
of nature was still too rudimentary. Our photography couldn't yet capture the right details.
Only now are our labs and our math catching up with the stunning sophistication of creatures
around us. We've learned to look to the sea to understand the air. And, we finally see what a
thing of beauty that lumpy humpback whale flipper really is.
I'm John Lienhard at the University of Houston, where we’re interested in the way inventive minds work.
F. E. Fish, P. W. Weber, M. M. Murray, and L. E. Howle, The Tubercles on Humpback Whales' Flippers:
Application of Bio-Inspired Technology. Integrative and Comparative Biology, vol. 51, No. 1, pp. 203-213.
The lead author of this article, Frank Fish, is also a founding member of
WhalePower Corporation, a
company commercializing tubercle-enhanced blades of all kinds. See also
this online article by Fish.
My thanks to Stephen Dewar of WhalePower Corp. for his counsel. Dewar made a point that I have
not emphasized in this episode: It is how radically tubercle-enhanced flow over a blade differs
from conventional flow over an airfoil. The vortices emanating from the tubercles are completely
unlike the straight flow of air over conventional wings.
This episode was first aired on March 18, 2014
The Engines of Our Ingenuity is
Copyright © 1988-2013 by John H. Lienhard.