Dynamics of macro-vortices in horizontal axis turbine wind farms

Johns Hopkins University, Baltimore MD

Investigators

Abstract

Fluid dynamics and turbulent flow phenomena are known to play dominant roles in the performance, efficiency and environmental impact of wind farms. There is growing interest in using fluid dynamics knowledge to improve wind energy harvesting and thereby achieve societal benefits such as reduced greenhouse gas emissions and a renewable energy economy. This research project aims to develop air flow models for use in wind plant design and control. The working hypothesis is that flow modifications resulting from turbine actions, such as adjusting the angle of the turbine rotor to the incoming flow (yawing or tilting) or pulsing the surfaces that regulate power extraction, can best be understood using models of very large swirling flow structures called "macro-vortices." Such vortices are believed to extend for many hundreds of meters downstream of turbines in a wind farm. These structures can be responsible for changing the speed, direction, and frequency of the wind exiting a turbine and impacting the performance of downstream turbines. This research project will use computer simulations to study the generation, evolution, and decay of large-scale vortices in turbulent flows. Educational and outreach activities will leverage national and international research networks through Johns Hopkins University Society of Women Engineers. K-12 outreach will be coordinated through the Center for Educational Outreach at Johns Hopkins University and will include lectures as part of Engineering Innovation, a summer program for high school students. The project researchers will also participate in an intersession program at a local elementary school. This research project will develop the fundamental knowledge required to harness the potential of large-scale flow actuation, using wind turbine yaw, tilt, and cycling, in order to improve wind farm performance. Various research questions will be addressed using high-fidelity numerical datasets from a suite of Large Eddy Simulations (LES) of yawed, tilted, and periodically forced turbines. The project will characterize the properties (strength, effective core-size, positions and trajectories) of the macro-vortices generated under various conditions, including shear, surface roughness, and thermal stratification of the atmosphere, e.g. under buoyant (daytime) and stably stratified (nighttime) conditions. The project will develop reduced models that leverage lessons learned from the various LES data, as well as from basic physics of vorticity dynamics and simplified descriptions such as lifting line theory. The resulting reduced models and LES insights will be used to find improved arrangements or optimal networks of macro-vortices. The objective would be to increase vertical entrainment of mean kinetic energy from the faster winds above the wind turbines down into the wind turbine region. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.