Whale tubercles improve wind turbines

Challenge: more efficient wind turbines

Natural solution: humpback whale Megaptera novaeangliaeoffshore wind turbines © Jesper Baerentzen, www.sxc.hu

 

 

Wind is a plentiful renewable resource.  Carefully-sited wind turbines are an environmentally and economically sustainable way of producing energy.  The UK, with the largest wind energy resource in Europe, 1 could potentially generate a fifth of its electricity needs from wind power. 2  Globally, wind could meet a significant proportion of humanity’s energy needs, and the amount of energy generated by wind power is growing rapidly each year.  However, wind still only provided about 0.5% of total global energy production in 2004.3windy day © Photomorgana/ Dreamstime

 

 

 

 

One of the main limitations to wind power is its unpredictable nature.  Everyone is familiar with the way the wind constantly changes speed and direction.  Engineers aim to make wind turbines that are both reliable and efficient in the prevailing wind conditions.  However, there is a trade off: designs that can get the most energy out of high-speed winds perform very poorly at low wind speeds, and few designs can cope well with turbulent air. 4   The main problem is the phenomenon known as stalling.  Aeroplanes can stall when the flow of air over the wings is disrupted, causing a dramatic loss of lift which can cause the plane to plunge to earth.  Exactly the same thing occurs in wind turbine blades, but here stalling causes loss of power and can in extreme cases tear the turbine apart.  To work efficiently at low wind speeds, turbine blades need to meet the wind at a steep angle – a large ‘angle of attack’ – but this makes stalling more likely. 5  broken wind turbine © Gkanivets/ Dreamstime

 

 

Historically, wind turbine engineers have been forced to compromise, with the result that wind energy is not dependable enough to meet demand and has to have a fossil-fuel back up.  For every 200 megawatts of wind power, at least 100 megawatts of coal power are needed to fill in the gaps when wind power is not sufficient. 4

 

The accepted wisdom is that the leading edge of objects like wings, fins and humpback whale © ErezShor/ Dreamstimeturbine blades should be smooth and streamlined, and up until recently wind turbine designs have been based on this principle. 4   However, in the 1990s a biomechanics expert became interested in humpback whales.  These whales are extremely agile swimmers, using their mobile flippers to bank and turn to catch their prey; 6 and yet the flippers are clearly not smooth, being covered along the leading edge with bumps called tubercles.  A flipper was taken from a dead whale for detailed study.  It was found to be shaped very much like an aeroplane wing in cross-section, apart from the tubercles. 7  More studies followed, where models of flippers with and without tubercles were built and tested in wind tunnels. 6, 8  These revealed that the tubercles gave the flipper more lift and less drag, while allowing the angle of attack to be increased by 40% before stalling occurred.  Finally, in 2008, mathematicians managed to refine their fluid dynamics models to explain this phenomenon. 9  Decades of mathematical modelling had been overturned by simply observing how nature solves the problem. Engineers could now start to develop more efficient wind turbine designs by adding a bumpy leading edge to the blades.

 

 

This innovation has already been put to commercial use: a major Canadian company is producing industrial fans using the tubercle principle, which it claims are 20% more efficient than conventional fans.  However, the inventors of ‘Tubercle Technology’ see wind turbines as the main technology which will benefit from their discovery.  Modelling has shown that adding bumps to the leading edge of turbine blades directly addresses the stalling problems described above.  The product is currently being field tested, and the company is already receiving enquiries from wind turbine manufacturers. 4

 

littered beach © Massimo Valicc/ Dreamstime

 

 

 

 

Humpback whales belong to the cetaceans, a group of over 80 species of mammals including whales, dolphins and porpoises.   Within this group, they are one of the 13 species of baleen whale. 10  Although humpbacks, like other whales, have historically been killed in large numbers for their oil, they are now legally protected and populations are recovering in many places.  However, they are still threatened by habitat loss, chemical and noise pollution, entanglement in fishing nets, decline of the species they feed on, and illegal hunting.   Some isolated populations may still be at risk of extinction. 11

 

 

 

 

 

 

 

Humpback whale © Metropoway 893/ Dreamstime

Humpback whales are undeniably a charismatic species.  Thanks to their specialised flippers, they are the most acrobatic of the whales, renowned for their energetic displays.  The flippers, at up to 5m long,  are the largest appendage of any animal on earth.  Humpback whale tails (‘flukes’) are as unique as human fingerprints, and the way they raise them when diving enables whale-watchers to identify and track individual whales.  Male humpbacks sing the longest, most complex songs in the animal kingdom. 11  Hundreds of travellers, whale-watchers and scientists have marvelled at them and fought for their conservation over the years.  However, who could have predicted that they might one day help to solve the energy crisis by inspiring a better wind turbine?

 

 

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References

 

  1. Tucker, G., Bassi, S., Anderson, J., Chiavari, J., Casper, K. and Fergusson, M. (2008): Provision of Evidence of the Conservation Impacts of Energy Production. Institute for European Environmental Policy (IEEP), London, [201] pp. & Annexes.  Accessed March 2010.
  2. UK Government’s Department for Energy and Climate Change (2009) The UK Renewable Energy Strategy.  Accessed March 2010.
  3. IPCC: Sims, R.E.H. et al. (2007) Energy Supply.  In Climate Change 2007: Mitigation.  Contribution of working group III to the Fourth Assessment Report of IPCC.  Cambridge University Press, Cambridge.
  4. WhalePower Accessed March 2010
  5. Humpback whales inspire new wind turbine technologyTribology and Lubrication Technology, 2008.  Ed. Dr Neil Canter.   Accessed March 2010.
  6. D. S. Miklosovic et al. (2004) Leading-edge tubercles delay stall on humpback whale (Megaptera novaeangliae) flippers.  Physics of Fluids 16 doi:10.1063/1.1688341.  Full article available online.  Accessed March 2010.
  7. Fish F.E. et al. (1995) Hydrodynamic design of the humpback whale flipper. Journal of Morphology 225: 51-60.
  8. Derrick Custodio et al. (2006) Separation Control on a Hydrofoil Using Leading Edge Protuberances.  Bulletin of the American Physical Society, 59th Annual Meeting of the APS Division of Fluid Dynamics. 
  9. van Nierop, E. A. et al. (2008) How Bumps on Whale Flippers Delay Stall: An Aerodynamic Model. Physical Review Letters 100, 054502 
  10. Threatened species of whales and dolphins.  World Wide Fund for Nature (WWF).  Accessed March 2010. 
  11. Whale and Dolphin Conservation Society (WDCS).  Accessed March 2010.


Further reading


Offshore renewable energy, JNCC.  Accessed March 2010.

Whales And Dolphins Influence New Wind Turbine Design.  Science Daily, July 2008.  Accessed March 2010.

Whales, Dolphins Inspire Wind Turbine Tech.  Discovery News, July 2008.  Accessed March 2010.