Size of rotating domain

Adam

I am simulating a rotating turbine in a wind tunnel. The values of measured rotational velocity and torque are my reference. I set the problem as a rotating domain (turbine) inside a stationary domain (wind tunnel). The calculated values are affected by choosing rotating domain size. I choose it 1*Diameter of the rotor, 1.5 Diameter and 3*Diameter. For 1Diameter and 1.5 Diameter case the value of calculated torque on turbine blades is over predicted compared with experiment. While in the 3rd case (3*Diameter) the value is under predicted. What should I do? What is the correct domain size?

Other interesting phenomena that initial position of the blades affect the torque value. The value of the torque is changed when I draw the blades as vertical or horizontal. As the domain is rotating torque should not be affected by the initial position. Is this correct?