Taking Inspiration from Mother Nature

E-mail Melanie Martella

What do schools of fish and wind farms have in common? At first glance, not much, since fish are aquatic and edible and wind farms are land-based (even if they're trying like heck to have wind farms off the coast of Cape Cod) and aren't edible unless you're a metal-eating bacterium. However, in another example of using tricks from nature to inform modern technology, the fluid dynamics used by schools of fish have inspired a more efficient way to cluster wind turbines without losing power efficiency.

Learning from Fish
Let's take the fish first. We are, by now, pretty familiar with horizontal-axis wind turbines (HAWTs); huge, spare machines, gently spinning away and dotted across farmland all over the country. They do what they're designed to do and they do it well, but you can't plonk a bunch of them down too close to each other or the airflow downstream from one turbine interferes with the airflow to the next, resulting in a drop in the power produced. If we want to get more wind power from the same amount of land and we can't get more just by adding more HAWTs, what do we do? Robert Whittlesey, Sebastian Liska, and John Dabiri from the California Institute of Technology have an answer to that; use vertical axis wind turbines (VAWTs) instead. Individually, a VAWT doesn't produce anything like the energy produced by the more traditional HAWT type and costs more to boot, but if you place multiple VAWTs in close proximity, you can actually get boosted performance. And this is where the fish come in.

When a school of fish swims along, they create something called a Karman vortex street, a nifty fluid dynamic phenomenon that serves to keep the fish aligned in the school and lessens the amount of energy they expend while swimming along. By creating a VAWT array that paired closely spaced, counter-rotating VAWTs, the researchers found that they could reduce the land use for VAWT wind farms, with array power density increases of more than one order of magnitude when compared to operational HAWT wind farms. Neat, huh? If you're champing at the bit to learn more, I'd suggest reading their paper "Fish schooling as a basis for vertical axis wind turbine farm design".

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