What do I do when

Orb · October 26, 2012, 16:51

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, 06:10

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, 08:01

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

cdegroot · October 28, 2012, 08:31

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, 13:06

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, 16:15

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, 16:42

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

ghorrocks · October 28, 2012, 16:48

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

Orb · October 28, 2012, 16:56

Hehe that is my problem it is intellectual property

ghorrocks · October 28, 2012, 16:58

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, 20:09

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

ghorrocks · October 28, 2012, 20:47

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, 21:05

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, 21:44

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, 12:22

Quote:

Originally Posted by ghorrocks

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?

ghorrocks · October 30, 2012, 16:51

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

October 26, 2012, 16:51	What do I do when	#1
Orb Member Join Date: Jan 2012 Posts: 52 Rep Power: 14	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.

October 28, 2012, 20:09		#14
Orb Member Join Date: Jan 2012 Posts: 52 Rep Power: 14	*************************** Last edited by Orb; October 28, 2012 at 21:11.

October 27, 2012, 07:31		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	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.

October 27, 2012, 11:45		#3
Orb Member Join Date: Jan 2012 Posts: 52 Rep Power: 14	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?

October 27, 2012, 20:11		#4
Orb Member Join Date: Jan 2012 Posts: 52 Rep Power: 14	Immersed Solid fails too - weird streamlines..

October 28, 2012, 06:10		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	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.

October 28, 2012, 08:01		#6
Orb Member Join Date: Jan 2012 Posts: 52 Rep Power: 14	It looks like I need to perform a rotating moving mesh for this... But I cannot find any tutorials online.

October 28, 2012, 08:31		#7
cdegroot Senior Member Chris DeGroot Join Date: Nov 2011 Location: Canada Posts: 414 Rep Power: 17	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.

October 28, 2012, 13:06		#8
Orb Member Join Date: Jan 2012 Posts: 52 Rep Power: 14	So do I do a subtract boolean of the fill? I am not understanding how many parts I need for that.

October 28, 2012, 16:15		#9
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	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.

October 28, 2012, 16:42		#10
Orb Member Join Date: Jan 2012 Posts: 52 Rep Power: 14	I cannot use a rotating reference frame. This is not an axial propeller.

October 28, 2012, 16:48		#11
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	What sort of propeller is it then? Can you post an image?

October 28, 2012, 16:56		#12
Orb Member Join Date: Jan 2012 Posts: 52 Rep Power: 14	Hehe that is my problem it is intellectual property

October 28, 2012, 16:58		#13
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	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.

October 28, 2012, 20:47		#15
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	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.

October 28, 2012, 21:05		#16
Orb Member Join Date: Jan 2012 Posts: 52 Rep Power: 14	Hmm I think I see it now. Do I just create a spherical rotating frame? Instead of a cylinder like in the tutorials.

October 28, 2012, 21:44		#17
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	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.

October 30, 2012, 16:51		#19
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	I think he removed the post after I had looked at it. I suspect he does not want to publicise his idea too much.