New Models for Vertical-Axis Wind Turbines

We’ve become familiar with wind-turbines pockmarking the landscape. Recently, an alternative design, the vertical-axis wind turbine (VAWT), received a boost when a group of researchers at Caltech showed that they could use them to produce ten times more power than using conventional turbines. To better understand how they interact with the wind, researchers at EPFL’s WIRE lab developed two new computer models, which they tested against experimental data. They published their findings in Energies on February 20, 2014.

Vertical-axis wind turbines have a number of advantages over tradition horizontal-axis ones. They are always oriented towards the wind, and because their mechanical parts are at ground level, and not atop a high mast, repair and maintenance work can be performed at a much lower cost. Although some studies point at the heightened sensitivity to mechanical wear, these shortcomings could be overcome with more research and development. And now, at least in the research community, they are increasingly receiving more attention.

The shadow of the wind
But in wind farms, both turbine designs face a common challenge. The wake they cast often creates a turbulent wind-shadow on downwind turbines, dramatically reducing the productivity of the turbines within the wind farm by up to 40% compared to those in the frontlines. One way to avoid this could be by setting up the turbines in such a way that they actually benefit from the turbulence produced by their neighbors. This was recently shown by researchers from Caltech’s Biological Propulsion Lab who found that certain wind farm arrangements allow to pack more turbines onto a given area, dramatically increasing the electricity produced.

To better understand the effect of the layout of a wind farm on its power production, Sina Shamsoddin developed two computer models that simulate the effects of the turbine blades on the wind for his Master’s thesis in EPFL’s Program for Energy Management and Sustainability. While the first, simpler model uses a constant force, distributed over the surface swept by the blades, to model the interaction between the turbine blades and the wind, the second, more detailed model distributes these forces along lines that represent the actual position of the blades as they cut through the air.

To find out how well the computer models performed, he then compared the simulation results to measurements made on a miniature wind turbine in the laboratory. Not surprisingly, the second, more detailed model did a better job at replicating measurements made in a wind tunnel. In particular, it was capable of reproducing the irregular flow patterns downstream of the wind turbines. But as the authors of the paper state in their article, the slight superiority of this more sophisticated model could be offset by the much higher needs of computing power it needs to run.