Mystery of the Dolphin's Speed

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/-sear...8-3190/1/2/001 . (there is a PDF file of the study referenced here)
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.”