The effect of rotational direction on the wake of a wind turbine rotor - a comparison study of aligned co- and counter rotating turbine arrays

Various concepts have been investigated in wind turbine research to improve the productivity of wind farms. However, there are some strategies, which offer further potential for improvement. One of these concepts is the rotational direction of a wind turbine, which has influence on its wake characteristics and development. In this study the effect of rotor rotational direction of an upwind turbine on the performance of another wind turbine operating in its wake was investigated. Two model wind turbines with the same rotor diameter, in-line arrangement, are used for this study. The upstream wind turbine was operated either co-rotating or counter-rotating with respect to the downstream wind turbine and the distance between the turbines was varied between 2.0D and 5.15D (where D is the rotor diameter). The performance and wake measurements of the turbine arrays were investigated using both numerical and experimental approaches. By operating the upstream turbine in counter-rotating direction with respect to the downstream turbine, the combined productivity of the two turbines was found to have improved. This improvement is significant at 3.5D, where the productivity was observed to increase by 2.0%.