A shoal of turbines (Wind Spire Energy)

Can the flicking tails of schooling fish help squeeze more power out of a wind farm? A group of aeronautical engineers seem to think so.

Inspired by the turbulence created by fish schools, they are now testing whether it’s possible to position wind turbines so that they help each other – and so boost a farm’s energy output.

Wind farm turbines tend to fall into two types. Three-bladed, horizontal-axis wind turbines are more common – the world’s biggest HAWT farm opened off the coast of Kent, UK this week. However, a new breed of vertical axis wind turbines (VAWT) are on the up and up.

VAWTs feature a vertical shaft around which airstream-intercepting wings swirl (see Picture). The “lift” of the wind tangentially yanks the turbine around.


Their advantage? They can harvest airflow from all directions, plus are cheaper to maintain than standard turbines because their generators and gearboxes are on or near the ground.

One downside is that an individual VAWT is less efficient than a typical three-rotor turbine, says aeronautical engineer John Dabiri at Caltech in Pasadena.

However, HAWTs are not perfect. They have to be spaced wide apart – up to 10 times their rotor diameter – to avoid the blades of a neighbouring turbine slowing down the wind too much. That means building them offshore or where there is plenty of land.

VAWTs churn up less of the surrounding air. So Dabiri and colleagues wanted to find out if packing them as tight as possible could rival the overall efficiency of a typical wind farm.

Thought of school

As they did so, inspiration struck Dabiri: “It occurred to me that the equations I was writing were the same as I had previously seen in models of the vortices in a school of fish. From there it was just connecting the dots, conceptually speaking,” he says.

One reason fish swim en masse is that it allows them to travel two to six times further than when swimming solo. In 1973, Daniel Weihs of the University of Cambridge (Nature, DOI:10.1038/241290a0) suggested that the vortices shed by the tail of a fish in a school sets the surrounding water moving faster so that neighbouring fish get a speed boost.

Could turbines in air help each other too? By modifying the hydrodynamic fish equations for aerodynamics and then feeding them into a fluid dynamics model, they were able to work out optimum turbine placements.

A VAWT farm positioned in this way could generate 10 times the power of a HAWT farm of the same area. “We’re proposing that VAWTs can be a more effective solution even for large-scale utility power generation,” he says.

Class test

Now the team are putting their idea to the test. This summer, the Caltech team operated six vertical turbines north of Los Angeles. The turbines are around 10 metres tall and were mounted on mobile platforms.

The platforms allowed the team to move the turbines to test the most efficient wind farm layouts. They compared their results to those from a HAWT farm on a similar plot of land.

For now, Dabiri is keeping the results close to his chest – saying only that they are “promising” – but he has been encouraged enough to press ahead with patent applications and to seek further tests. “The next step will hopefully be a larger-scale field demonstration,” he says.

Robert Blake of the University of British Columbia, Canada and guest editor of the edition of the journal that the work appeared in says the study is “innovative” and “illustrates that biological systems can provide good models for engineering.”

Thorsteinn Sigfusson, director-general of the Innovation Center Iceland in Reykjavik, adds: “In countries like my own where the wind is unsteady and changes direction quickly [VAWTs] could be a major contribution. I look forward to hearing how their larger scale tests go.”

Journal Reference: Biomimetics and Bioinspiration, DOI:10.1088/1748-3182/5/3/035005

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