Wind Turbine Wake Measurements in the Operating Region of a Tail Vane

Document Type

Conference Presentation

Conference Title

2001 ASME Wind Energy Symposium


American Society of Mechanical Engineers


Reno, NV

Conference Dates

January 8-11, 2001

Date of Presentation



In conjunction with the National Renewable Energy Laboratory's (NREL'S) Unsteady Aerodynamics Experiment (UAE) at NASA Ames, we measured the wake of an upwing 10 meter (m) diameter wind turbine in the typical region of a tail vane. The experiment was performed in a 24.4- by 36.6-m wind tunnel. We placed two sonic anemometers 0.58 rotor diameters downwind of the rotor at hub height. One was positioned nominally behind the nacelle at 9% radius and the second was placed 2-m outboard at 49%. The tunnel wind speed was varied from 5 to 25 meters per second (m/s) and the turbine rotor speed was held at 72 revolutions per minute (rom). We varied yaw from 0° to 60°. The data showed unsteadiness in the wake due to the nacelle wake. Also, the unsteadiness increased with the onset of blade stall. The axial induction factor in the wake showed that the turbine was operating within the windmill brake state of actuator disk momentum theory. Little variation in unsteadiness was shown under yawed conditions. We also discovered that lateral velocity behind the nacelle was negative and would result in an unfurling normal force on a tail vane. The vertical velocity was shown to change sign under yawed conditions, conceivable as a result of the opposing blade root vortex