Measurement of flow deflection effects around an offshore wind farm caused by global blockage

Abstract The Global-Blockage Effect, i. e. the accumulated induction zone of a whole wind farm, can reduce upstream wind speeds and is expected to deflect the incoming wind upwards and sideways. While wind speed deficits were observed in free field experiments, there is no experimental evidence for global blockage induced diverging flows and their strengths in front of large wind farms. We aim for the experimental confirmation of flow deflections to the sides of a wind farm due to global blockage. We analyse long-range scanning lidar data in the inflow of a large offshore wind farm for diverging wind directions. In a previous study we detected global blockage induced velocity deficits using the same data set. We found significant local flow direction differences in the sectors left and right of the stream-wise centre line of the wind farm indicating the flow to be deflected to the wind farm sides. We conclude that not only wind speed deficits but also wind direction changes are caused by the Global-Blockage Effect and both should be considered in accurate modelling.