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Orb October 26, 2012 16:51

What do I do when
 
I am not able to model a rotating (non-stationary) fluid domain? The geometry of my propeller won't allow it and just using the fill command (with the subtract Boolean operation) and solid-fluid interface (to stationary fluid around the propeller) won't work.

ghorrocks October 27, 2012 07:31

CFX supports rotating frames of reference. That is what all the people talking about turbo machinery models are using. But solids in rotating frames has only been supported in V14 I think. Earlier versions do not support it.

Why do you want to use a solid-fluid interface? Are you modelling heat transfer in the propeller? If you are not modelling heat transfer then you do not need to model the solid.

Orb October 27, 2012 11:45

The propeller device is solid, because I am not able to build a rotating reference frame of fluid around it. The geometry doesn't allow it I don't think. Do I need a rotating reference frame? Can't I just rotate the solid inside of stationary fluid?

Orb October 27, 2012 20:11

Immersed Solid fails too - weird streamlines..

ghorrocks October 28, 2012 07:10

Have you done the CFX tutorials on turbomachinery and other rotating frames of reference simulations? That will show you how to step this sort of thing up.

Orb October 28, 2012 09:01

It looks like I need to perform a rotating moving mesh for this... But I cannot find any tutorials online.

cdegroot October 28, 2012 09:31

You are modeling a propeller? I am sure there are many ways to model this, but a moving mesh is not an efficient choice to make. As ghurrocks said, a rotating frame of reference is the right choice and there is no reason to mesh the solid if you are just doing a fluid dynamics analysis. Moving the solid inside a stationary fluid will just be more costly computationally and won't give any better results.

Orb October 28, 2012 14:06

So do I do a subtract boolean of the fill? I am not understanding how many parts I need for that.

ghorrocks October 28, 2012 17:15

There are plenty of tutorials which come with CFX which describe how to do this. You can get to them from the CFX documentation, in the tutorials manual.

Orb October 28, 2012 17:42

I cannot use a rotating reference frame. This is not an axial propeller.

ghorrocks October 28, 2012 17:48

What sort of propeller is it then? Can you post an image?

Orb October 28, 2012 17:56

Hehe that is my problem it is intellectual property :(

ghorrocks October 28, 2012 17:58

We are not going to be able to help you much until we have some idea of what you are modelling. Reduce it down to a simple model which shows the key motion but does not cause IP issues. Or point us to a public-domain thing which is close.

Orb October 28, 2012 21:09

***************************

ghorrocks October 28, 2012 21:47

Still looks like a rotating frames of reference simulation to me. Just that the axis of rotation is not aligned with the flow. You can define the rotation axis to be any vector, so it will handle this.

Orb October 28, 2012 22:05

Hmm I think I see it now. Do I just create a spherical rotating frame? Instead of a cylinder like in the tutorials.

ghorrocks October 28, 2012 22:44

A RFR can only have one axis and it cannot change. But it can be anywhere in any direction.

So if your gizmo only rotates about one axis then use RFR. If it rotates about 2 axes you need to do this as a moving mesh or immersed solids model and the accuracy will reduce and run time will be FAR longer.

k.vafiadis October 30, 2012 13:22

Quote:

Originally Posted by ghorrocks (Post 388991)
Still looks like a rotating frames of reference simulation to me. Just that the axis of rotation is not aligned with the flow. You can define the rotation axis to be any vector, so it will handle this.

I can only see "***************************" as an answer from Orb, what's the geometry?:confused:

ghorrocks October 30, 2012 17:51

I think he removed the post after I had looked at it. I suspect he does not want to publicise his idea too much.


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