Tandem positioning increases power output for micro wind turbines

Most people picture wind turbines as massive structures hundreds of feet tall, generating megawatts of power. However, small scale micro wind turbines, with a diameter smaller than 200 mm across, provide a different approach, generating decentralized power for remote sensors or other electronic devices disconnected from a power grid.

Zhang et al. investigated the dynamics involved in a pair of micro wind turbines operating in tandem, with one positioned directly behind the other.

Using stereoscopic particle image velocimetry, the team analyzed the wake dynamics and power gain from both co-rotating and counter-rotating arrangements of turbines placed between three and 12 radii apart. They found that incorporating a second, counter-rotating rotor at a distance of 12 radii increased the power gained from the system by 37% over a single rotor.

“Surprisingly, the counter-rotating arrangement consistently outperforms the co-rotating one — even at short distances, where wakes are highly turbulent and energy recovery is challenging,” said author Michaël Pereira.

Their experimental data showed that the wake from the first turbine still contained rotational energy that could be harvested by the rear turbine. This is because smaller turbines operate at a lower tip-speed ratio and lower Reynolds numbers, resulting in higher torque and imparting rotational energy into the wake.

The authors hope their results will spur increased efforts to maximize the efficiency of micro wind turbines.

“This work opens new paths for optimizing compact wind energy systems,” said Pereira. “It suggests that, much like multi-stage turbines in jet engines, micro wind turbines could benefit from tailored downstream designs — harvesting not only the wind’s push, but also its twist.”

Source: “Experimental study of two low tip-speed ratio micro-scale wind turbines operating in tandem,” by Shuo Zhang, Michaël Pereira, Florent Ravelet, and Alfred Boyer, Journal of Renewable and Sustainable Energy (2025). The article can be accessed at https://doi.org/10.1063/5.0250680 .