Wind energy is one of the most promising renewable energy sources in the world today. A Doctor from Iowa State University and his team studied the effects of the relative rotation direction of two tandem wind turbines on power generation performance, flow characteristics in turbine wakes, and the effect of the resulting wind load on the turbine.
In a typical wind farm, due to the upwind turbine wake interference, wind turbines located in the wake of upstream turbines will experience significantly different surface winds than wind turbines located upwind. Based on the spacing and layout of the wind turbine array, it was found that the power loss of downstream turbines was up to 40% due to wake interference. Therefore, how to increase the power generation of downstream wind turbines is one of the most important research topics in recent years. Recently, extensive experimental and numerical studies have been conducted to examine aerodynamics of wind turbines and wake interference among the multiple wind turbines. In order to gain an in-depth understanding of the basic physics of higher total power generation and better durability of wind turbines.
Although most wind turbines in modern wind farms are single-rotor wind turbine (SRWT) systems, the concept of a counter-rotating wind turbine (CRWT) system has been proposed in recent years. Because of the azimuth velocity generated in the wake behind the wind turbine, it rotates in the opposite direction to the upstream rotor. Therefore, the downstream rotor should rotate in the same direction as the eddy wake of the CRWT system in order to extract energy from the wind wake more efficiently.
The wake interferences among SRWT systems with different rotation directions in a wind farm have never been investigated before. Considering this, experiments are conducted to quantify the influence of the relative rotation direction of two series wind turbines on the wake interference between turbines. Although the oncoming flow remained constant during the experiment, the model turbine was set to rotate in the same direction (i.e. the downstream turbine has the same rotation direction as the upstream turbine) or reverse rotation (i.e. the opposite rotation direction of the upstream turbine). The turbine power output, static and dynamic wind loads acting on the turbine and the turbulence characteristics in the wake behind the turbine are measured and compared quantitatively.
It turns out that turbines that rotate in the opposite direction harvest more wind energy from the same head-on wind than turbines that rotate in the same direction. Although the recovery of flow-velocity defects in the wake was found to be almost identical to that of turbines rotating in the same or opposite direction. But the significant azimuth velocity generated in the wake behind the upstream turbine is thought to be the reason for the better power generation performance of the counter-rotating turbine.