Measurement of Truck Cab Flow in Support of Wind Turbine Testing

Document Type



Mechanical Engineering

Report Number



National Renewable Energy Laboratory

Publication Date


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Last Page




WindLite Corporation of Mountain View, California, developed an 8-kW wind turbine under the U.S. Department of Energy’s Small Wind Turbine Project. WindLite proposed testing the turbine on a truck flatbed while driving the truck down a runway at constant relative wind speed. The primary objective of the truck test was to optimize the turbine’s furling behavior. The data could also be used to advance furling analytical models. A concern at the beginning of the test program was what influence the truck cab would have on the rotor inflow and thus the turbine behavior. Therefore an experiment was proposed to measure the rotor inflow without the turbine installed.


We constructed an array of anemometers to measure the airflow at locations around an area representative of the rotor disk. The array could also be yawed to measure the inflow at yawed rotor positions. A reference anemometer and wind direction sensor were positioned forward of the truck cab at turbine hub height. We first calibrated the array anemometers against the reference anemometer on a rig placed forward of the cab. The array was then erected with the anemometers and the truck was driven down the runway at speeds and yaw angles representative of turbine operation. The array anemometer data were then normalized to the reference anemometer wind speed.


The data showed that at wind directions below 5 ° off the truck line of travel, the influence of the cab on the rotor inflow was negligible with exception to the lower-most sector of the rotor disk. This area was characterized by increased turbulence and wind speed deficit that increased with wind speed.