In the realm of wind energy research, a team of scientists from the University of Minnesota, including Aliza Abraham, Luis A. Martinez-Tossas, and Jiarong Hong, have been delving into the complex behaviors of wind turbine wakes. Their recent study, published in the Journal of Fluid Mechanics, aims to better understand how wind turbine wakes respond to dynamic changes in atmospheric conditions and operational parameters.
Wind turbines operate in a constantly changing environment, with wind speeds and directions fluctuating and turbine operations, such as blade pitch and yaw angle, adjusting in response. However, most studies on wind turbine wakes assume quasi-steady conditions, where changes happen slowly enough to be considered constant. This new research challenges that assumption and investigates the transient response of utility-scale wind turbine wakes to dynamic changes.
The researchers used large eddy simulations, a sophisticated computational fluid dynamics method, to model the wake of a utility-scale wind turbine. They found that when the blade pitch changes, the wake expansion response displays hysteresis, a phenomenon where the system’s response lags behind changes in the input. This lag is due to the inertia of the flow and the timescales of this response were quantified for different pitch rates.
Next, the team explored how the wake responds to changes in wind direction. Under short timescales, they observed that the wake deflects in the opposite direction of that observed under quasi-steady conditions. To understand this inverse wake deflection, they quantified the streamwise vorticity, or the rotation of the flow along the axis of the wind turbine, in different parts of the wake.
Finally, the researchers implemented yaw changes at different rates and quantified the maximum inverse wake deflection and timescale, showing a clear dependence on yaw rate. They found that the lag in wake response observed for both blade pitch and yaw changes must be considered when designing advanced wake flow control algorithms. Specifically, turbine operational changes should be implemented with a timescale on the order of the rotor timescale or slower to account for this lag.
This study provides valuable insights for the wind energy industry, particularly for the development of dynamic control strategies aimed at optimizing wind farm power generation and longevity. By understanding and accounting for the dynamic behaviors of wind turbine wakes, operators can make more informed decisions about turbine operations, ultimately leading to more efficient and productive wind farms.
This article is based on research available at arXiv.