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

Using stage interface

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 20, 2010, 10:44
Default Using stage interface
  #1
ijk
Member
 
Join Date: Apr 2010
Posts: 33
Rep Power: 7
ijk is on a distinguished road
Dear all,

My question is regarding the use of a stage interface.

I am modelling a fan blowing air through a radiator.

Is it valid to model one fan passage out of seven and the entire radiator and to use a stage interface between the two? The radiator is square. In other words do I need to model the full fan for this case?

I am considering using the downstream velocity constraint "constant total pressure" so that the downstream velcoity can be adjusted due to the impact of the radiator.

Thanks,

ijk
ijk is offline   Reply With Quote

Old   October 21, 2010, 07:50
Default
  #2
Senior Member
 
Attesz's Avatar
 
Attesz
Join Date: Mar 2009
Posts: 355
Rep Power: 8
Attesz is an unknown quantity at this point
With the stage option the fluxes will be averaged at the interfaces. The problem in your case is the high pitch ratio. You will get an 51deg periodic domain in a rotating frame of reference with the periodic side 1 and the radiator's stage will have 360 deg, so the pitch ratio will be about 7 which is high, and you can get very inaccureate results easily. I think, you should use the radiator as a periodic model, or if you can't do so, use the entire model. On the boundaries, mass flow or pressure values are better, except you have the velocity profile measured.

If you can, post some picture about the geometry.
Attesz is offline   Reply With Quote

Old   October 26, 2010, 11:11
Default
  #3
ijk
Member
 
Join Date: Apr 2010
Posts: 33
Rep Power: 7
ijk is on a distinguished road
Thank you for your response.

I cannot simulate one quarter of the radiator due to its heat transfer.

I do not understand why the computational accuracy would degrade with increasing pitch change if the values of flow variables apart from pressure are simply averaged and passed downstream.

The manual says:

"The computational accuracy degrades rapidly with increasing pitch change. It is recommended that sufficient blade components be analyzed on each side of the interface to minimize pitch change. Any pitch change will result in a non-physical transient interaction: the entire 360 degree components must be solved for truly “accurate” transient interactions if the pitch ratio is non-integer. Small pitch changes will introduce relatively smaller errors, large pitch changes will introduce larger errors. "
ijk is offline   Reply With Quote

Old   October 26, 2010, 22:31
Default
  #4
Senior Member
 
Michael P. Owen
Join Date: Mar 2009
Posts: 195
Rep Power: 8
michael_owen is on a distinguished road
ijk,

You are correct; the solution will not be degraded because of the pitch change, because it is an integer ratio (7).

Now the real question you should be asking is not "Can I use a stage with a 7:1 pitch change" but rather, is a stage interface appropriate at all? If the latter is true, then the pitch change is irrelevant as long as it's integer.

You need to calculate r*omega and compare it to the through velocity of the fan. If it's much greater than the through speed, then the stage approximation starts to become appropriate.
michael_owen is offline   Reply With Quote

Old   October 27, 2010, 07:11
Default
  #5
ijk
Member
 
Join Date: Apr 2010
Posts: 33
Rep Power: 7
ijk is on a distinguished road
Thanks Michael,

Your response helped clarify things a lot. My average through speed is about a fifth of the tip speed. Good to see you keep yourself busy with CFD whilst on the bench. How's the hamstring?

ijk
ijk 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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Wind turbine simulation Saturn CFX 41 February 2, 2016 07:48
Questions about STAGE interface pad CFX 3 April 28, 2010 09:08
RPM in Wind Turbine Pankaj CFX 9 November 23, 2009 05:05
Stage Interface Without Frame Change Vikram CFX 2 October 21, 2005 04:55
Replace periodic by inlet-outlet pair lego CFX 3 November 5, 2002 21:09


All times are GMT -4. The time now is 06:00.