BES: Unraveling interactions between extreme-scale wind power systems and stratified, turbulent environmental flows

Abstract:

To meet net-zero carbon emissions targets by mid-century, up to a ~30-fold increase in wind power capacity is required. To expand energy production, wind turbines are rapidly increasing in size, wind farms are proliferating to new locations and are increasing in size and siting density, and novel wind farm design and control methods are increasingly deployed. But current engineering models driving wind power design and control rely on idealized theory that neglects key aspects of rotor operation within the turbulent, stratified, and sheared atmospheric boundary layer, which are increasingly important for larger turbines and farms. We revisit the first-principles of mass, momentum, and energy conservation to develop a Unified Momentum theory for rotors across operating regimes, accounting for arbitrary misalignments between rotor and inflow and thrust coefficients. The model is validated against large eddy simulations and unique high Reynolds number experiments performed in a pressurized wind tunnel. The Unified Momentum Model generalizes and replaces both classical momentum theory and the Betz limit and further reveals a new opportunity to improve wind farm flow control through synergistic combination of wake steering (yaw) control and induction (thrust) control. Moreover, wind turbines always operate in complex atmospheric boundary layer conditions which violate the uniform assumptions in existing rotor aerodynamics theories. We reveal that wind speed and direction shear (veer) trigger rotor efficiency losses that can exceed 20%, are not captured in existing engineering models, and increase as wind turbines grow in size. Going from the scale of a turbine to a farm, wake losses can reduce farm energy by 30%, a significant loss that negatively impacts economics and is increasing given wind power expansion. Using large eddy simulations of wind turbines operating in a range of atmospheric conditions, we systematically uncover the significant roles of Coriolis effects and atmospheric stability on wake recovery, trajectory, and morphology. We develop a new fast-running TANDEM (Turbulence ANd DEficit Momentum) wind farm model which accounts for the coupled rotor operational and atmospheric effects on wakes and yields lower error than existing wake models. We perform collective flow control based on the wind farm model, applied in both simulations and utility-scale field experiments. Full-scale field experiments demonstrate that collective flow control increases the energy generation of wind farms through software modifications, without additional turbines or hardware.

Biography:

Michael F. Howland is the Jeffrey Cheah Career Development Professor of Civil and Environmental Engineering at MIT. He was a Postdoctoral Scholar at Caltech in the Department of Aerospace Engineering. He received his B.S. from Johns Hopkins University and his M.S. from Stanford University. He received his Ph.D. from Stanford University in the Department of Mechanical Engineering. His work is focused at the intersection of fluid mechanics, weather and climate modeling, uncertainty quantification, and optimization and control with an emphasis on renewable energy systems. He uses a synergistic combination of simulations, laboratory and field experiments, and theoretical modeling to improve the understanding, efficiency, predictability, and reliability of low-carbon energy systems. At Stanford, he received the Tau Beta Pi scholarship, NSF Graduate Research Fellowship, and a Stanford Graduate Fellowship. At MIT, he has received the Maseeh Excellence in Teaching Award, the Office of Naval Research (ONR) Young Investigator Program (YIP) award, and an NSF CAREER award.