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

Time steps in transient run with heat transfer

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

Reply
 
LinkBack Thread Tools Display Modes
Old   December 7, 2005, 09:44
Default Time steps in transient run with heat transfer
  #1
Linda
Guest
 
Posts: n/a
I have done a transient simulation i CFX. The flow is a turbulent flow in an (almost) straight pipe. The heat loads are linearly ramped up from around 100 K to 600 K during one second.

When the boundary layer at the wall is resolved (y+<1)I need to set a time step of about 1.5*10^-5 s. (This is the size of the physical time step from the steady state run) Otherwise the solver gives the following error: "floating point exception", and is then terminated.

If y+ is about 5 instead the time step needs to be about 0.004 s for the solution to converge. This is also a smaller time step than is desired.

It is obvious that there is a connection between the resolution of the grid, and the resolution in time. Can anyone explain why this is? There is not supposed to be any limitations of the maximum size of the time step since the solver in CFX uses an implicit method for the integration of time.

I would be grateful for an insight in this problem.

Thank you /Linda
  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
How to write k and epsilon before the abnormal end xiuying OpenFOAM Running, Solving & CFD 8 August 27, 2013 15:33
Conjugate Transient Heat Transfer Jaap FLUENT 0 May 24, 2008 16:09
IcoFoam parallel woes msrinath80 OpenFOAM Running, Solving & CFD 9 July 22, 2007 02:58
time steps in transient heat transfer in solids Mike Main CFD Forum 3 June 5, 2003 05:47
time averaged heat transfer in oscillating flow Matthieu Ubas Main CFD Forum 2 November 5, 1999 15:20


All times are GMT -4. The time now is 03:53.