Wind Turbine Wake Modeling

Accurate prediction of wind turbine wakes in the atmosphere is one of the main challenges in state-of-the-art wind energy research. It is well accepted that the interaction of wind turbine wakes with downstream turbines within a wind turbine array (or wind farm) leads to decreased array efficiency and increased blade fatigue. – Our group investigates this difficult problem by modeling the wakes of wind turbines in an Atmospheric Boundary Layer (ABL). In our research efforts, we are using Actuator-Line Modeling (ALM), which represents wind turbine blades as distributed momentum sources in the governing fluid-dynamics equations, i.e. Reynolds-Averaged Navier-Stokes (RANS) or Large-Eddy Simulation (LES). We are using the OpenFOAM framework for our simulations. We have also identified some shortcomings in current ALM w.r.t. the accuracy at which the blade loads are modeled by the distributed momentum sources. Our group interacts closely with researchers at the National Wind Technology Center (NWTC) to investigate potential improvements to ALM towards a better prediction of sectional blade loads. Furthermore, we are very interested in the effect of atmospheric turbulence on blade loads, the physics of the wake momentum deficit, and the power production of an array of wind turbines. Our developments are an integral part of the Cyber Wind Facility project at Penn State. Of particular interest is the interaction of wind turbines with turbulent eddies in a Moderately Convective Boundary Layer (MCBL). At present, we are also investigating various turbulent statistics extracted from our high-resolution numerical data that will enhance the physical understanding of the interaction of blade tip vortices with turbulent atmospheric structures, turbulent momentum transport into the rotor disk area of downstream wind turbines, and the generation mechanism of wake meandering.