Wind farms with counter-rotating wind turbines

The objective of this study is to assess the effects of using counter-rotating wind turbines on the performance of a wind farm. Large eddy simulations, coupled with the actuator line model, were conducted to investigate flow through a test wind farm with 48 large-scale wind turbines with the same layout as Lillgrund in Sweden. Two counter-rotating cases were tested; first, an alternate-row wind farm in which each turbine has one rotor, rotating either clockwise or counter-clockwise, with alternating rows of clockwise and counter-clockwise turbines throughout the farm; and second, a wind farm with dual-rotor wind turbines in which each turbine has two rotors, with the first rotor rotating counter-clockwise and the second rotor rotating clockwise. It was found that both counter-rotating configurations were more efficient in power generation than the control case in which all turbines have one clockwise rotor; the alternate-row case was found to produce 1.4% more power and the dual-rotor case was found to produce 22.6% more power than the control wind farm. The wakes of the counter-rotating cases, particularly the wind farm with dual-rotor wind turbines, exhibit different characteristics from those in the control case. These differences are discussed through wind speed distribution, thrust coefficient, and power production of wind turbines.