Wind energy has become a promising renewable energy source over the years with large wind farms being built worldwide. These wind farms produce hundreds of megawatts (MW) of power utilizing multi-megawatt wind turbines. The operation of a wind turbine is affected by many factors, however the ingestion of wakes from other turbines results in reduced power output and increased dynamic loading on the turbine blades. In an effort to minimize the cost of the wind farm, turbines are typically located in close proximity, resulting in the interaction and merging of many wakes in the wind farm. Previous studies indicate that estimated power losses due to wakes can range from 5% to 20%, depending upon the wind farm layout.
Although modeling of wind turbine wakes has been a research topic for nearly 30 years, analysis of wake interactions has typically used simple wake models that predict velocity and other flow variables in the wake using a set of explicit equations or analytical expressions. With today?s computational resources it is now possible to perform high-resolution simulations for multiple wind turbines with rotating blades by solving the Navier-Stokes equations without introducing a wake model. Although this approach would provide a higher fidelity representation of wind-turbine flow with wake interaction, the computer run time would range from days to weeks. Thus, there is need to have improved field simulation models and wake models that are both high fidelity and sufficiently economical to perform the large number of simulation cases required to effectively design and optimize the layouts of wind farms so as to minimize the adverse affects of wake ingestion. Additionally, such a combined model could be used to improve estimates of power production from existing wind farms by integration with continually updated wind climate (speed and direction) forecasts. Accurate power production forecasts are necessary for economical operation of the wind farm and to reduce power-grid stability issues.
This project will explore two new, high-fidelity, low-cost computational models for wind-turbine wakes and wake interactions. The first is a new Parabolic Navier-Stokes model based on a primary/secondary flow approximation that allows spatial marching solution without any approximation for pressure gradients. It can be used in steady mode with time-independent turbine-disk models or in unsteady mode with rotating-blade models. It will improve upon existing models by being applicable not only in the far wake but also in the near-wake region. Its computational cost for simulating flow through a wind farm would be substantially lower (orders of magnitude) than a Navier-Stokes simulation. The second model for wake and wake-interaction will involve decomposing Navier-Stokes simulations into modes using techniques such as Proper Orthogonal Decomposition or Dynamic Mode Decomposition. This model will significantly reduce the computational cost compared to the Parabolic Navier-Stokes model. In the area of wind farm layout optimization, this study will address methods for coupling a global optimization algorithm with a gradient-based algorithm to mitigate their deficiencies and reduce overall wall-clock time for optimization.
The SimCenter, an integrated research and education center within the University of Tennessee at Chattanooga, has been involved in a broad range of STEM activities that support the goal of stimulating interest among students in K-12 in science and math related disciplines. It regularly hosts dozens of groups of K-12 students over the course of the year. It also maintains a website dedicated to STEM related resources. As part of this proposed effort, these activities will be expanded to respond to interest from local museums in collaborations to reach a wider audience. A table-top model of a wind farm will be created and used as part of the tours that are conducted. This will enable students to have hands-on experience with functioning wind turbines. High school, undergraduate and graduate students will be involved in various aspects of this activity. The high-school and undergraduate students will be involved in developing the table-top model and will also develop software applications for the SimCenter website. In addition, undergraduate students will assist in the generation of computational grids required for the simulations, and graduate students will implement the approaches outlined in this proposal.
