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

oscillations 1D3D coupling GT-Power/StarCD

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

Reply
 
LinkBack Thread Tools Display Modes
Old   May 29, 2005, 12:21
Default oscillations 1D3D coupling GT-Power/StarCD
  #1
Hubert Janocha
Guest
 
Posts: n/a
When I couple the 1D Software GT-Power with StarCD sometimes I get very high oscillations at the interface volumen of GT and Star. I already have testet many ideas, but I still have not found an overall reproduceable error to avoid this oczillations. Some ideas / tricks helps, but not enough.

The application is a intake manifold calculation for normal asperated or turbo charged combustion engines.

It is strange, because this oscillations occur in that time steps when the pressure gradients are very low (means: in that time when the intake valve is cllosed). When the intake valve opens I get a very good high quality devolution / distribution of mass and velocities.

I hope strongle anybody is out there with an advice.
  Reply With Quote

Old   June 6, 2005, 05:42
Default Re: oscillations 1D3D coupling GT-Power/StarCD
  #2
Steve
Guest
 
Posts: n/a
Your Courant number is probably too high at the boundary for the explicit 1D code to be stable. If this is the case, your options are:

1) Decrease your timestep.

This may not be as bad as it seems, because STAR-CD may converge more quickly with a smaller step, only marginally increasing total runtime.

2) Increase the mesh size at the boundaries.

Counter-intuitive perhaps, but it will improve stability. Ideally make the mesh size (in the normal direction) equal to your 1D code's discretization.
  Reply With Quote

Old   June 6, 2005, 05:43
Default Re: oscillations 1D3D coupling GT-Power/StarCD
  #3
Steve
Guest
 
Posts: n/a
Incidentally, what did the GT people recommend?
  Reply With Quote

Old   June 6, 2005, 16:25
Default Re: oscillations 1D3D coupling GT-Power/StarCD
  #4
Hubert Janocha
Guest
 
Posts: n/a
They recommand exactly what you have sad. Additionally the Flow in the interface volumen has to be straight, means without curvs / bends.

The problem is, that I get oscillations at times of low pressure gradients !!! So decreasing the time step is not a remedy, because the velocity is low.

Do you have similar problems?
  Reply With Quote

Old   June 7, 2005, 04:50
Default Re: oscillations 1D3D coupling GT-Power/StarCD
  #5
Steve
Guest
 
Posts: n/a
I don't actually run GT with STAR-CD, but I do have several years of 1D/3D experience. And in my experience, step-to-step velocity oscillations are always caused by high Courant numbers at the boundary, regardless of local flow conditions. Just for reference, 1D explicit codes are generally less stable at low flows than at high flows (noise takes over).

Out of interest, what is your boundary mesh size (in the normal direction) and what timestep size (in seconds) are you using? Also, how many steps does the 1D code take for each STAR-CD step?
  Reply With Quote

Old   June 9, 2005, 16:30
Default Re: oscillations 1D3D coupling GT-Power/StarCD
  #6
Hubert Janocha
Guest
 
Posts: n/a
Steve, hold on, I will come back to you.
  Reply With Quote

Old   June 25, 2005, 19:54
Default Re: oscillations 1D3D coupling GT-Power/StarCD
  #7
Hubert Janocha
Guest
 
Posts: n/a
Steve,

I am still alive. The problem is very important to me, but currently I can't produce results from a test case, because other things have a much more higher priority and time is hurrying, but I will come back to you. Sorry, I hope you will be still here.

So long Hubert
  Reply With Quote

Old   July 4, 2005, 06:58
Default Re: oscillations 1D3D coupling GT-Power/StarCD
  #8
Steve
Guest
 
Posts: n/a
Still watching, but rapidly getting RSI from scrolling the mouse right down here...
  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
1D3D Coupling GT-Power/StarCD Hubert Janocha CD-adapco 16 August 15, 2010 08:03
1D3D GT coupling :intake manifold convergence prob Micky CD-adapco 1 June 20, 2008 23:02
1D3D GT coupling:how to read the cfd file Micky CD-adapco 1 June 20, 2008 22:56
1D3D-Coupling StarCD GT-Power Hubert Janocha CD-adapco 3 November 15, 2005 13:43
Coupling GT-Power w Star 324 in 1 CPU (win XP) Le Vu CD-adapco 1 September 6, 2005 08:15


All times are GMT -4. The time now is 09:58.