Realizing the potential of periodically surging turbines for increased power production

In full-scale applications, wind and tidal turbines must contend with unsteady flow conditions. In particular, a turbine encountering streamwise unsteadiness may experience either enhancements or losses in its time-averaged power production, depending on the nature of the perturbation and the characteristics of the turbine. In this work, we seek to identify and model the mechanisms responsible for these divergent outcomes. First, single-point velocity and pressure measurements were conducted upstream and downstream of a periodically surging horizontal-axis wind turbine in a fan-array wind tunnel. Surge-velocity amplitudes up to 23% of the wind speed were examined. Then, a turbine surging through amplitudes of up to 40% of the mean flow speed was studied using two-dimensional particle-image velocimetry in an optical towing tank. Flow kinematics were measured both on the turbine blades and in the wake up to 15 diameters downstream of the turbine. These two datasets facilitated the development of analytical models that highlighted factors responsible for the observed changes in time-averaged power. These results can inform the design and control of turbines operating in unsteady conditions for increased efficiency and robustness against flow disturbances.