Vertical-axis wind turbine experiments at full dynamic similarity

Laboratory experiments were performed on a geometrically scaled vertical-axis wind turbine model over an unprecedented range of Reynolds numbers, including and exceeding those of the full-scale turbine. The study was performed in the high-pressure environment of the Princeton High Reynolds number Test Facility (HRTF). Utilizing highly compressed air as the working fluid enabled extremely high Reynolds numbers while still maintaining dynamic similarity by matching the tip speed ratio (defined as the ratio of tip velocity to free stream, lambda = omega R/U) and Mach number (defined at the turbine tip, M alpha = omega R/alpha). Preliminary comparisons are made with measurements from the full-scale field turbine. Peak power for both the field data and experiments resides around lambda = 1. In addition, a systematic investigation of trends with Reynolds number was performed in the laboratory, which revealed details about the asymptotic behaviour. It was shown that the parameter that characterizes invariance in the power coefficient was the Reynolds number based on blade chord conditions (Re-c). The power coefficient reaches its asymptotic value when Re-c > 1.5 x 10(6), which is higher than what the field turbine experiences. The asymptotic power curve is found, which is invariant to further increases in Reynolds number.