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Size of rotating domain

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?

 Glenn Horrocks November 26, 2006 17:25

Re: Size of rotating domain

Hi,

The best way to model it is to model exactly what you are trying to match. This means you should model the wind tunnel geometry, preferably with the upstream components as well.

Glenn Horrocks

 Bian November 27, 2006 13:10

Re: Size of rotating domain

This is interesting!!!

I would assume your 1*Diameter domain is set the Rotor-Stator interface right at the outer diamter of the rotor. This may be too close to the wake of the blade.

But where is suitable to set the interface is an art. If everything is axisymmetrical, the initial position should not affect the overall parameters. In your case, it is really strange. Is the torque reading measured very stable?

Re: Size of rotating domain

The torque reading in experiment is unstable. The difference between the 1.5 * Diameter and 3*Diameter case torque is too big. I made an interpolation between the 3 results. I found that the size of the domain should be 1/2 tunnel size. I am trying this now I hope I am right.