Wind tunnel test results for a 2/4.5 scale MEXICO rotor

This paper presents the wind tunnel test results from MEXNEXT, an IEA wind task for analyzing the measurements which have been taken in the EU project ‘MEXICO’. A 2/4.5 scaled model of ‘MEXICO’ rotor was tested in the KARI low wind tunnel with 5 × 3.75 m2 open jet test section. The aerodynamic performance of the blade which was represented by the torque was measured in the wind speed from 0 to 30 m/s by using the torque sensor installed in the rotating axis. The rotational speed of the rotor was controlled by the electric motor to keep the prescribed blade tip speed from 50 m/s to 90 m/s. Two different surface conditions, free and forced transition conditions were used for all blade tip speeds. Transition dots with 0.18 mm height were attached at the 5% chord line on both sides of the blade surface for the forced transition condition. The torque coefficients with respect to the wind speed coefficient for the forced transition condition show same characteristics for all blade tip speed conditions except for the stall region. But, the torque coefficient for the free transition condition gradually increases as the blade tip speed increases until the tip speed reaches 76 m/s and it has the similar value above that speed. The comparison result between the free and the forced transition conditions at the blade tip speed 76 m/s shows that the torque coefficient for the former case is 30% higher than the latter case. The computational results from ‘Rfoil’ and the BEMT method also shows that the aerodynamic performance of the rotor for the forced transition condition is lower than the free transition one at the wind tunnel test condition.

► A wind tunnel test for a 2/4.5 scaled ‘MEXICO’ rotor was conducted.
► The torque generated by the blade was measured in the wind speed 0–30 m/s.
► Blade performance for the forced transition case is same for all rotation speed.
► Blade performance for the free transition case varies with the rotation speed.
► Torque for the free transition case is 30% higher than the forced transition case.