Contrasting blade flow field archetypes in the HAWT operating regime

Abstract

Horizontal axis wind turbines (HAWT's) routinely suffer significant time varying aerodynamic loads that exercise adverse effects on structures, mechanical components, and power production. As lighter and more flexible wind energy machines are designed to reduce overall cost of energy, greater accuracy and reliability will become even more crucial in future aerodynamics models. Aerodynamics modeling advances will, in turn, rely on improved understanding of the three-dimensional, unsteady, vortical flows that reside on turbine blades under high load conditions. To experimentally characterize these flows, the National Renewable Energy Laboratory (NREL) Phase VI Unsteady Aerodynamics Experiment (UAE) turbine was erected in the NASA Ames National Full- Scale Aerodynamics Complex (NFAC) 80 foot x 120 foot wind tunnel. Then, under strictly controlled inflow conditions, turbine blade surface 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 vortices 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 pronounced, dynamic stall vortex deformation. Analysis of these data revealed systematic alterations to vortex kinematics due to changes in wind speed, yaw error, and blade span location. NOMENCLATURE