Whales Inspire New Turbine Blades
Turbine blades inspired by whales (that's the mammals and not a misspelling of the country Wales) show promise in delivering improved efficiency and operational range. This example of reverse engineering of a naturally evolved design (referred to as biomimicry) demonstrates that nature is still a rich resource of inspiration for traditional engineering disciplines.
Our typical assumption about whales is that they are large lumbering sea-bound mammals. Not so, said a team of researchers (Frank Fish, Laurens Howle, David Miklosovic and Mark Murray) who were intrigued by the relative nimbleness of 44-foot long humpback whales and went in search of the cause. The team focused their attention on the humpback's flippers, which have a distinct saw-tooth-like structure along their leading edges, called tubercles. They performed a comparison with an equivalent smooth flipper in a wind tunnel and found that the tubercle design:
- Had 8 percent more lift
- Stalled at 40 percent higher angle of attack
- Had up to 32 percent less drag
The aerodynamic efficiency of the tubercle flipper was a surprise to say the least and has implications for all aerodynamic devices that use wings, such as airplanes, helicopters, racing cars and turbines.
While efforts continue to investigate the cause of the aerodynamic performance improvements due to tubercles, it appears that the effect is similar to that of using vortex generators or dimples on golf balls. The vortices shed from the tubercles appear to energize the downstream flow such that it is less likely to stall compared to an equivalent smooth design. Simulations of fluid flow over flippers with tubercles performed using Computational Fluid Dynamics (CFD) show the leading edge vortices coalescing into stable segregated recirculations at the trailing edge. Recirculations are usually a sure sign of stall, and therefore increased drag, but this reasoning doesn't seem to apply to the tubercle flipper.
Fish was so impressed with his findings that he founded a company (WhalePower) to develop and license designs using tubercles. The first company (Envira-North Systems) to license the technology incorporated the tubercles into a ceiling fan and claim to have improved performance and lowered energy costs. More recent work has focused on using tubercles on wind turbine blades to improve their performance. So far the results are promising.
The story of tubercles makes for a great case study in innovation:
- Using biomimicry to reverse engineer a naturally evolved design
- Analysis performed by a combination of traditional wind tunnels tests and the latest CFD methods
- Lateral thinking in proposing tubercles for aerodynamic applications after observing their hydrodynamic performance
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