MIT engineers have unveiled a new, physics-based model for rotor aerodynamics that could revolutionize the design and operation of wind farms. The model addresses long-standing challenges in accurately predicting the performance of wind turbine blades, especially under extreme conditions, and can potentially optimize wind farm layouts and turbine operations in real time. The National Science Foundation and Siemens Gamesa Renewable Energy supported the research.
For over a century, the design of turbine blades and propellers has relied on aerodynamic principles that, while foundational, often fall short in complex scenarios. Engineers have traditionally used ad hoc “correction factors” to account for these discrepancies. However, MIT’s new model offers a comprehensive solution that accurately represents airflow around rotors, even at high forces, speeds, and angles. This breakthrough is detailed in a paper published in Nature Communications by MIT postdoc Jaime Liew, doctoral student Kirby Heck, and Professor Michael Howland.
“We’ve developed a new theory for the aerodynamics of rotors,” said Howland, the Esther and Harold E. Edgerton Assistant Professor of Civil and Environmental Engineering. “This theory can be used to determine the forces, flow velocities, and power of a rotor, whether that rotor is extracting energy from the airflow, as in a wind turbine, or applying energy to the flow, as in a ship or airplane propeller.”
The new model has immediate applications in optimizing wind farm operations. Operators adjust turbine parameters, such as orientation, rotation speed, and blade angles, to maximize power output while maintaining safety. The new model can streamline these adjustments, offering a faster, more precise method to optimize turbine performance.
“This is what we’re so excited about,” Howland noted, “It has immediate and direct potential for impact across the value chain of wind power.”
The traditional momentum theory, which dates back to the late 19th century, provided the basis for understanding rotor dynamics. This theory allowed engineers to predict the maximum power that could be extracted from wind, a calculation refined by physicist Albert Betz in 1920. Known as the Betz limit, this theoretical maximum is 59.3% of the kinetic energy of the incoming wind.
However, the momentum theory fails at higher forces and speeds, inaccurately predicting the direction and magnitude of changes in thrust force. Howland’s team discovered that the original model’s assumptions about air pressure dynamics were incorrect, especially near the Betz limit, where turbines are expected to operate at maximum efficiency.
To address these shortcomings, the MIT researchers developed a unified momentum model that accurately predicts rotor performance, even when the rotor is misaligned with the airflow—a common scenario in wind farms. The new model draws from aerospace engineering principles and was validated through computational fluid dynamics modeling. Future validation is planned using wind tunnel and field tests.
One surprising outcome of this research is slightly modifying the Betz limit, suggesting that turbines can extract slightly more power than previously thought. Although the change is marginal, it underscores the significance of the new model in refining long-held assumptions about wind energy.
The model’s implications extend beyond wind turbines to include propellers for aircraft and ships and hydrokinetic turbines used in tidal and river energy. The MIT team has made the model available as an open-source software package on GitHub, allowing engineers and researchers to integrate it into their own tools for rapid prototyping and optimization.
“This breakthrough is a natural extension of our previous work on optimizing utility-scale wind farms,” Howland said. “Our theory can directly tell you, without any empirical corrections, for the first time, how you should actually operate a wind turbine to maximize its power.”
