Analytical Model for Phase Synchronization of a Pair of Vertical-Axis Wind Turbines

Abstract

The phase-synchronized rotation of a pair of closely spaced vertical-axis wind turbines has been found in wind tunnel experiments and computational fluid dynamics (CFD) simulations. During phase synchronization, the two wind turbine rotors rotate inversely at the same mean angular velocity. The blades of the two rotors pass through the gap between the turbines almost simultaneously, while the angular velocities oscillate with a small amplitude. A pressure drop in the gap region, explained by Bernoulli’s law, has been proposed to generate the interaction torque required for phase synchronization. In this study, an analytical model of the interaction torques was developed. In our simulations using the model, (i) phase synchronization occurred, (ii) the angular velocities of the rotors oscillated during the phase synchronization, and (iii) the oscillation period became shorter and the amplitude became larger as the interaction became stronger. These observations agree qualitatively with the experiments and CFD simulations. Phase synchronization was found to occur even for a pair of rotors with slightly different torque characteristics. Our simulation also shows that the induced flow velocities influence the dependence of the angular velocities during phase synchronization on the rotation directions of the rotors and the distance between the rotors.

Method to Predict Outputs of Two-Dimensional VAWT Rotors by Using Wake Model Mimicking the CFD-Created Flow Field

“…Their CFD analysis considering the time-varying rotor speed, for the first time, simulated the synchronization operation of twin rotors and showed the alternation in the angular velocities of two rotors. Furukawa et al [36] developed an analytical model considering the pressure fluctuation (or increase in flow velocity) observed in the gap region between twin rotors in the above experiments and CFD analyses. The model successfully demonstrated the alternation in the angular velocities of two rotors and showed that the period of the variation in rotor speed depended on the strength of the interaction between the two rotors.…”

Advancements in Offshore Vertical Axis Wind Turbines

“…In addition, the authors show, using a surrogate model, that turbine spacings can be optimised based on the resulting wake dynamics. Another study by Furukawa et al [15] proposes a model for quantifying the interacting torques as a result of the VAWT rotor phase synchronisation. More advanced studies on floating VAWT wake interactions, taking into account pitching motions, can be found in Kuang et al [16].…”