Wind tunnel test for the NREL phase VI rotor with 2 m diameter

The aerodynamic performance of the ‘NREL Phase VI’ rotor with a 2 m diameter was tested in the open jet test section. The original rotor with a 10.06 m diameter was tested in the NASA Ames tunnel and the test result was used as validation data for the computational model. The Reynolds number of the sectional airfoils in the original test is around 1.0E6 which is too high for a conventional wind tunnel with a diameter less than 5 m. The wind tunnel test to study the Reynolds number effect on the rotor performance from Re = 0.1E6 to Re = 0.4E6 was conducted in the KARI low speed wind tunnel with a 5 m × 3.75 m open jet test section. The torque generated by the blade was directly measured by the sensor installed in the rotating axis. The variation of the Reynolds number was achieved by changing the rotational speed. Two surface conditions, free transition and forced transition were employed in this test to study the surface trip effect. The test results for the free transition condition show that the power coefficient, Cp gradually increases with the Reynolds number, but the Cp for the forced transition condition does not vary with the Reynolds number. The maximum Cp for the free transition is 0.30 and it decrease to 0.22 for the forced transition conditions at the Reynolds number 0.4E6. The downstream flow velocity measured by 5-hole probe in the wind tunnel test was compared with BEMT calculation result. The comparison results show that the torque dependency on Reynolds number in the blade is mainly originated from the airfoil drag characteristics. A model to estimate the power of full scale blade was suggested based on these measurement results. The estimated power shows a good agreement with the full scale test result.