Wake characteristics of closely spaced vertical axis wind turbines

In order to optimally arrange the vertical axis wind turbines in the wind farm, it is necessary to understand the wake distribution behind the turbines. In this study, wind tunnel tests were conducted on two adjacent Darrieus rotors with straight blades to evaluate the wake expansion, wind speed reduction and wind speed distribution. The wind speed was measured using a hot-wire anemometer from just behind the rotor to a distance of 12 times the rotor diameter. The dual turbines rotating at the arrangements of clockwise and counter-clockwise revealed different wake distributions. On the side where the rotating direction of the rotor coincided with the inflow wind, the wind velocity accelerated and the wind speed decelerated on the opposite side. As the distance from the wind turbine increases, the wind speed recovery through the space between the two rotors was greatly affected by the direction of rotation of the two rotors, and the wind speed varied by up to 11% at distance of 12 times the rotor diameter.