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Connecting a rotating and a stationary domain

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Old   April 20, 2017, 12:44
Unhappy Connecting a rotating and a stationary domain
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Dear CFD-experts,

Im a student at a german university and trying to simulate a uav (airplane) in Ansys CFX for a seminar paper. To include the effect of a turning prop I thought I could use an empty rotating domain connected to a stationary domain. I connected them by domain interfaces with following settings.

Interface Models:
- Option: General Connection
- Frame Change/Mixing Model: Frozen Rotor
- Pitch Change: Automatic

Now my problem is that the flux in the rotating domain stops rotating immediately at the end of the domain. Can you please give me instructions how to solve my problem?
Please compare my explanation to the attached picture of a simple test-simulation.

Test.JPG
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Old   April 20, 2017, 18:48
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Glenn Horrocks
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You have missed the entire point of frames of reference....

A frame of reference can be seen as simply a grid system against which velocities are measured. Whether the frame of reference is rotating or not makes no difference to the actual flow, only on what you measure its velocity as.

And empty domain, whether rotating or not, has no effect on the flow. And that is what you are seeing. The corkscrew streamlines in the rotating domain is explained in this FAQ: https://www.cfd-online.com/Wiki/Ansy...f_reference.3F

If you want to introduce some swirl into the flow then use a momentum source term with a function which swirling momentum. Do not use a rotating frame of reference, this can be done in the stationary frame of reference the rest of your model is in.
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Old   April 21, 2017, 05:20
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Dear ghorrocks,

thanks a lot for the fast response.

I have now added a momentum source to my simulation but i got a problem with the function which swirls the momentum. I searched the forum but i didnt find good examples or a way to create such a function. Ive got no experience with such things.
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Old   April 21, 2017, 19:50
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If the axis of the swirl is the origin, then

Theta = arctan2(y,x)
Radius = sqrt(x*x+y*y)
X_Mom_Source = C*Radius*sin(Theta)
Y_Mom_Source = C*Radius*cos(Theta)

Where C is the strength of the swirl in appropriate units. I forget if arctan2 is the correct function but it is something like that. You might also be able to do some simplification of it if you feel adventurous.
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Old   April 22, 2017, 07:31
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I Got it. Thanks a lot!
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