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Published January 2022 | Published + Submitted
Journal Article Open

Phase-averaged dynamics of a periodically surging wind turbine


The unsteady power generation of a wind turbine translating in the streamwise direction is relevant to floating offshore wind turbines, kite-mounted airborne wind turbines, and other non-traditional wind-energy systems. To study this problem experimentally, measurements of torque, rotor speed, and power were acquired for a horizontal-axis wind turbine actuated in periodic surge motions in a fan-array wind tunnel at the Caltech Center for Autonomous Systems and Technologies (CAST). Experiments were conducted at a diameter-based Reynolds number of Re_D = 6.1 × 10⁵ and at tip-speed ratios between 5.2 and 8.8. Sinusoidal and trapezoidal surge-velocity waveforms with maximum surge velocities up to 23% of the free-stream velocity were tested. A model in the form of a linear ordinary differential equation (first-order in time) was derived to capture the time-resolved dynamics of the surging turbine. Its coefficients were obtained using torque measurements from a stationary turbine, without the need for unsteady calibrations. Its predictions compared favorably with the measured amplitude- and phase-response data. Furthermore, increases in the period-averaged power of up to 6.4% above the steady reference case were observed in the experiments at high tip-speed ratios and surge velocities, potentially due to unsteady or nonlinear aerodynamic effects. Conversely, decreases in mean power with increased surge velocity at low tip-speed ratios were likely a result of the onset of stall on the turbine blades. These results inform the development of strategies to optimize and control the unsteady power generation of periodically surging wind turbines, and motivate further investigations into the unsteady aerodynamics of wind-energy systems.

Additional Information

© 2022 Author(s). Published under an exclusive license by AIP Publishing. Submitted: 20 October 2021. Accepted: 17 December 2021. Accepted Manuscript Online: 17 December 2021. Published Online: 02 February 2022. The authors gratefully acknowledge the assistance of several people, without whom the construction and operation of the experimental apparatus would not have been possible: J. Benson, who graciously provided machine-shop access during the pandemic; G. Juarez and M. Vega, who installed the power systems for the linear actuator; M. Miller, K. Bankord, and J. Kissing for technical consultation regarding the turbine power-control system and linear actuator; A. Kiani and E. Tang for machining key components of the apparatus; N. Esparza-Duran and R. Nemovi, who oversaw operations at CAST; M. Veismann and P. Renn for wind-tunnel support; and J. Cardona, E. Tang, P. Gunnarson, M. Fu, and R. Goldshmid for providing assistance and safety supervision for the experiments. This work was funded by the National Science Foundation (Grant No. CBET-2038071) and the Caltech Center for Autonomous Systems and Technologies. N. Wei was supported by a Stanford Graduate Fellowship and a National Science Foundation Graduate Research Fellowship. DATA AVAILABILITY. The data that support the findings of this study are available from the corresponding author upon reasonable request. The authors have no conflicts to disclose.

Attached Files

Published - 013305_1_online.pdf

Submitted - 2110-10312.pdf


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October 9, 2023
October 24, 2023