Mystery of the Dolphin's Speed

[brian eiland]

CFD Investigation, Mystery Of Dolphin's Speed

How do dolphins maintain a swimming speed of up to 10 m/s? Standard engineering calculations predict that the dolphin’s muscles would have to be seven times more powerful than they actually are to achieve that speed. An alternative explanation is that the dolphin somehow reduces the frictional drag on its skin through the water to a much lower level than experienced by other bodies in water. This might be possible if the dolphin were able to maintain laminar flow as opposed to turbulent flow, which would be expected at the speeds at which it travels. Laminar flow generates much less drag and so could account for the dolphin’s extraordinary speed.

Research scientist V.V. Pavlov at the Crimean State Medical University in the Ukraine used COSMOSFloWorks computational fluid dynamics (CFD) software to investigate this question, which has been known for 70 years as “Gray’s Paradox” after Sir James Gray who first pointed it out. Pavlov simulated the detailed hydrodynamics of the flow around the dorsal fin of the harbor porpoise (see the paper “Dolphin skin as a natural anisotropic compliant wall,” published in Bioinspiration & Biomimetics, http://www.iop.org/EJ/abstract/-search=14347319.1/1748-3190/1/2/001 .
COSMOSFloWorks is a SolidWorks product developed by Flomerics and uses the same underlying technology as the EFD.Lab, EFD.Pro, and EFD.V5 software products from Flomerics.

Pavlov found that the shape of the dolphin’s skin matches the flow conditions around the dorsal fin. He concluded that the skin structure appears to allow the flow-skin interface to behave as an anisotropic compliant wall in the regions of favorable and adverse pressure gradients on the skin. Apparently, by complying with flow conditions, the skin has the effect of suppressing instability growth in the boundary layer and reducing turbulence. This information may aid in the design of compliant walls that might increase speed and reduce fuel consumption of ships and airplanes, among other applications.

“The elegance of natural solutions inspires new ideas in technology and engineering,” Pavlov says. “The drag-reducing adaptation that dolphins have perfected over 50 million years is worth investigating because of their potential for improving the performance of human transport. By studying the relationship of the flow around the dolphin’s fin to the structure of its skin, we have gained insights that may prove very useful in designing compliant walls.

COSMOSFloworks played a crucial role in this analysis through its tight integration with SolidWorks 3D computer aided design (CAD) software,” Pavlov says. “We were able to perform direct analysis on the geometric model that we created of the dolphin’s fin, maintaining all the intelligence in the 3D CAD model. The CFD software makes it easy to perform flow simulation because it automatically analyzes the geometry and generates the computational grid in the background while the user interacts with the familiar CAD interface.”

[messabout]

Would that we had an understanding of the phenomena a little closer to ground level. Work by Pavlov and others is way up in the stratosphere for most of us.

I have wondered, along with others whether there is any substance to the claim that Baidarkas profited from some of this. The cultures that built the Baidarka almost surely developed them as a matter of survival rather than applying scientific knowledge. Tribes, at war over hunting grounds, were obliged to develope boats that were faster than their murderous rivals. Fortuitous accidents for the best of the boat builders, or instruction from extraterrestials, or divine intervention, or was skin compliance a factor at all.....???

[BWD]

skin compliance, overall motion (eg esp heave and yaw, etc) - all ideas that often are out of line with many common ways of looking at efficiency. dolphins swim, so do people.
A human freestyle swimmer develops something like 90% of his power in the upper body but the ones who win do so because they have the best form -they move their trunk and legs in a way that avoids drag. Try swimming like a dolphin, varying your sinusoidal pattern etc you may find sometimes you go twice as far.... that's at the macro level, and with a dolphin's body shape and mechanics, this is key too.
Not only is skin smooth and compliant but they apply a lot of power too, big pressure gradient/large scale vortices managed with body mechanics as well as skin... I think if you use something analogous to skin it would seem more like a paramecium... Just another angle ... Thanks for the article.

[Loveofsea]

i have seen female dolphins swim in such a way that they create and maintain a pocket of low pressure that their calf pops in and out of to breathe. Once in the pocket, the calf is drawn along with its mother and doesn't have to swim to stay with her. I find it interesting that a dolphin could project this force away from the actual surface of their skin. Birds flex certain feathers in flight to alter the foil of their wings also.