Wind Tunnel Measurements on a LM 8.2 m blade

The report presents wind tunnel measurements on a full scale 8.2 m long wind turbine blade. The same blade has previously been tested on a full scale 100 kW turbine and during these experiments local airfoil force coefficients C_N and C_T were measured at three radial stations along the blade. This was enabled by modifying the blade so that a 0.5 m long spanwise section of the blade shell at three radial stations was hinged on a balance mounted on the main spar. Correlation of the force measurements with measurements of the relative inflow vector by a five hole pitot tube led to derivation of the C_N and C_T coefficients. The same blade has now been tested in a wind tunnel of the closed return type with a 4x4 m jet blowing into a test chamber of 7.5x7.5 m and 10.5 m long, A maximum velocity if 33 m/s in the tunnel is close to the relative velocity for the blade rotating on the turbine.
The main objective with the wind tunnel measurements has been to provide a data set for two dimensional, nonrotating flow conditions for comparisons with the measurements on the same blade rotating on the turbine in order to study three dimensional flow effects, rotating effects and unsteady flow effects.
In the present report the measurement setup is described and an overview of the data is presented. Only measurements on the mid part of the blade has been carried out and this comprises both experiments where the angle of attack was changed stepwise as well as other experiments where the angle of attack was continously changed in order to simulate dynamic stall.