CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > CFX

What do I do when

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   October 26, 2012, 16:51
Default What do I do when
  #1
Orb
Member
 
Join Date: Jan 2012
Posts: 52
Rep Power: 5
Orb is on a distinguished road
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.
Orb is offline   Reply With Quote

Old   October 27, 2012, 07:31
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,826
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
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.
ghorrocks is offline   Reply With Quote

Old   October 27, 2012, 11:45
Default
  #3
Orb
Member
 
Join Date: Jan 2012
Posts: 52
Rep Power: 5
Orb is on a distinguished road
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 is offline   Reply With Quote

Old   October 27, 2012, 20:11
Default
  #4
Orb
Member
 
Join Date: Jan 2012
Posts: 52
Rep Power: 5
Orb is on a distinguished road
Immersed Solid fails too - weird streamlines..
Orb is offline   Reply With Quote

Old   October 28, 2012, 07:10
Default
  #5
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,826
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
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.
ghorrocks is offline   Reply With Quote

Old   October 28, 2012, 09:01
Default
  #6
Orb
Member
 
Join Date: Jan 2012
Posts: 52
Rep Power: 5
Orb is on a distinguished road
It looks like I need to perform a rotating moving mesh for this... But I cannot find any tutorials online.
Orb is offline   Reply With Quote

Old   October 28, 2012, 09:31
Default
  #7
Senior Member
 
Chris DeGroot
Join Date: Nov 2011
Location: Canada
Posts: 387
Rep Power: 6
cdegroot is on a distinguished road
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.
cdegroot is offline   Reply With Quote

Old   October 28, 2012, 14:06
Default
  #8
Orb
Member
 
Join Date: Jan 2012
Posts: 52
Rep Power: 5
Orb is on a distinguished road
So do I do a subtract boolean of the fill? I am not understanding how many parts I need for that.
Orb is offline   Reply With Quote

Old   October 28, 2012, 17:15
Default
  #9
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,826
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
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.
ghorrocks is offline   Reply With Quote

Old   October 28, 2012, 17:42
Default
  #10
Orb
Member
 
Join Date: Jan 2012
Posts: 52
Rep Power: 5
Orb is on a distinguished road
I cannot use a rotating reference frame. This is not an axial propeller.
Orb is offline   Reply With Quote

Old   October 28, 2012, 17:48
Default
  #11
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,826
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
What sort of propeller is it then? Can you post an image?
ghorrocks is offline   Reply With Quote

Old   October 28, 2012, 17:56
Default
  #12
Orb
Member
 
Join Date: Jan 2012
Posts: 52
Rep Power: 5
Orb is on a distinguished road
Hehe that is my problem it is intellectual property
Orb is offline   Reply With Quote

Old   October 28, 2012, 17:58
Default
  #13
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,826
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
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.
ghorrocks is offline   Reply With Quote

Old   October 28, 2012, 21:09
Default
  #14
Orb
Member
 
Join Date: Jan 2012
Posts: 52
Rep Power: 5
Orb is on a distinguished road
***************************

Last edited by Orb; October 28, 2012 at 22:11.
Orb is offline   Reply With Quote

Old   October 28, 2012, 21:47
Default
  #15
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,826
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
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.
ghorrocks is offline   Reply With Quote

Old   October 28, 2012, 22:05
Default
  #16
Orb
Member
 
Join Date: Jan 2012
Posts: 52
Rep Power: 5
Orb is on a distinguished road
Hmm I think I see it now. Do I just create a spherical rotating frame? Instead of a cylinder like in the tutorials.
Orb is offline   Reply With Quote

Old   October 28, 2012, 22:44
Default
  #17
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,826
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
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.
ghorrocks is offline   Reply With Quote

Old   October 30, 2012, 13:22
Question
  #18
New Member
 
Kyriakos Vafiadis
Join Date: Feb 2011
Location: Kozani, Greece
Posts: 27
Rep Power: 6
k.vafiadis is on a distinguished road
Send a message via Skype™ to k.vafiadis
Quote:
Originally Posted by ghorrocks View Post
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?
__________________
--
Kyriakos Vafiadis
Mechanical Engineer, PhD candidate
k.vafiadis is offline   Reply With Quote

Old   October 30, 2012, 17:51
Default
  #19
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,826
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
I think he removed the post after I had looked at it. I suspect he does not want to publicise his idea too much.
ghorrocks is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -4. The time now is 15:11.