Blade dynamic stall vortex kinematics for a horizontal axis wind turbine in yawed conditions

Horizontal axis wind turbines routinely suffer significant time varying aer odynamic loads that adversely impact structures, mechanical components, and power production. As lighter and more flexible wind turbines are designed to reduce overall cost of energy, greater accuracy and reliability will bec ome even more crucial in future aerodynamics models. However, to render cal culations tractable, current modeling approaches admit various approximatio ns that can degrade model predictive accuracy. To help understand the impac t of these modeling approximations and improve future models, the current e ffort seeks to document and comprehend the vortex kinematics for three-dime nsional, unsteady, vortex dominated flows occurring on horizontal axis wind turbine blades during non-zero yaw conditions. To experimentally character ize these flows, the National Renewable Energy Laboratory Unsteady Aerodyna mics Experiment turbine was erected in the NASA Ames 80 ft x 120 ft wind tu nnel. When, under strictly-controlled inflow conditions, turbine blade surf ace pressures and local inflow velocities were acquired at multiple radial locations. Surface pressure histories and normal force records were used to characterize dynamic stall vortex kinematics and normal forces. Stall vort ices occupied approximately two-thirds of the aerodynamically active blade span and persisted for nearly one-fourth of the blade rotation cycle. Stall vortex convection varied dramatically along the blade radius, yielding pro nounced dynamic stall vortex deformation. Analysis of these data revealed s ystematic alterations to vortex kinematics due to changes in test section s peed, yaw error, and blade span location.