Who cares about fish?

Or: Fresh findings on the fluid flow physics of fish flurry are both fun and fruitful.

As a physics grad student, I’m sometimes accused of esotericism by my non-technical friends.  And sometimes I agree.  It is hard to pursue a life’s work in science when you feel the tug of other causes.  But I also firmly believe that the advancement of science is important to the well-being and flourishing of the human race and that I can leave the world a bit better than I found it by making my own modest but original contributions to the wealth of human knowledge. But I admit it is hard sometimes to maintain trust in the worth of abstruse and seemingly irrelevant discoveries.

I was therefore pleased to read a paper in February on arXiv about the relationship between wind turbine farm design and the hydrodynamics of fish schooling.

Clockwise from top left: 1) The Brazos wind farm with horizontal axis wind turbines. (public domain, wikimedia commons user Leaflet). 2) A vertical axis wind turbine. (public domain, wikimedia commons user Aeolus88). 3) The hydrodynamics of fish schooling. (ref: arxiv.org/abs/1002.2250: Fish schooling as a basis for vertical axis wind turbine farm design).

Reference: Fish schooling as a basis for vertical axis wind turbine farm design

The paper itself is fairly accessible. And if your not in the mood to read it, the folks over at The Physics arXiv Blog have written a very nice review of the paper.  But if you’re not in the mood to read that either (slacker), here’s the gist:

Wind turbines come in a couple flavors: horizontal-axis and vertical-axis.  You’re probably used to seeing vertical-axis turbines, which typically have higher power output per turbine.  But they don’t play nice together; the turbulence created by the turbines in front attenuate the power output of the turbines in the rear.  The solution is to spread these horizontal-axis turbines out, thereby taking up more land.

Conversely, vertical-axis wind turbines typically have lower power output per turbine, but don’t have the same turbulent wakes that the horizontal-axis turbines do.  Whittlesey and the other Caltech folks who wrote the paper realized that an array of vertical-axis wind turbines is similar to a school of swimming fish (from a fluid dynamics perspective).  And what do you know, some guy named Daniel Weihs (reference #15 in their paper) studied the hydrodynamical aspects of fish schooling in 1975.  It turns out that not only can you pack the vertical-axis turbines (or fish) closer together, the leading turbines create vortices that can accelerate the current around the tailing turbines.  In other words, the fish draft off of each other and there’s no reason that we can’t exploit that behavior to increase the group power output of vertical-axis turbines.  So despite the lower power to unit ratio of the vertical-axis turbines, we can get a higher power to acre ratio than with horizontal-axis turbines.  Whittlesey claims that the power per unit area can increase by an order a magnitude.

This wind turbine stuff is interesting in its own right but my main point is this: Daniel Weihs’ research on fish schooling may seem esoteric, but it is no feat of mental masturbation.  In 1975, he probably had no idea that his modeling of fish schooling behavior would play a small but original role in solving the next century’s global climate crisis.  On the rare occasion that I doubt my choice to become a scientist or the importance of scientific literacy in public policy, I’ll think of fish power.  And once I’m done giggling, I’ll get back to work.