Prediction of Self‐Starting of a Vertical Axis Wind Turbine Using Static Torque

ABSTRACT The ability of vertical axis wind turbines (VAWTs) to self‐start is critical to their performance. There is disagreement in the literature over some of the factors affecting their self‐starting ability and there is very limited information on how the starting azimuthal angle affects self‐starting. We present a series of wind tunnel experiments in which we measure the static torque and self‐starting of a three‐blade VAWT for a range of initial azimuthal angles, which we find to have a very strong effect on the ability to self‐start. The blade pitch angle has a complex and non‐monotonic effect on the static torque and the probability of self‐starting, with self‐starting more likely when the static torque coefficient is large and uniform across all azimuthal angles. Increasing the freestream turbulence from to tends to induce peaks in the static torque coefficient at some angles, but leads to a relatively small improvement in self‐starting, while the addition of leading‐edge tubercles significantly improves self‐starting, ensuring the turbine self‐starts from almost any angle. Based on these insights, we introduce a quantitative criterion using the integral of the static torque curve to predict whether the turbine will self‐start for a given angle. Using an empirical threshold, this method can correctly classify 89% of the 189 cases presented in this study.