Blockage corrections in wind tunnel tests of small horizontal-axis wind turbines

This study quantitatively investigates the effects of tunnel blockage on the turbine power coefficient in wind tunnel tests of small horizontal-axis wind turbines (HAWTs). The blockage factor (BF), UTUF3, was determined by measuring the tunnel velocities with and without rotors using a pitot-static tube under various test conditions. Results show that the BF depends strongly on the rotor tip speed ratio (TSR), the blade pitch angle (β), and the tunnel blockage ratio (BR). The larger the TSR and BR are, the smaller the BF is. The BF approaches a constant value when the TSR exceeds a certain value. No blockage correction is necessary for small TSR under all of the investigated conditions, and for the investigated blade pitch angle of 25°. This study also shows that the blockage correction is less than 5% for a BR of 10%, which confirms that no blockage correction for a BR less than 10% in literatures is acceptable.