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

Adaptive Timestep in Eulerian Multiphase?

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

Like Tree2Likes
  • 1 Post By msaeedsadeghi
  • 1 Post By vig

Reply
 
LinkBack Thread Tools Display Modes
Old   January 23, 2013, 06:28
Question Adaptive Timestep in Eulerian Multiphase?
  #1
New Member
 
Bayard Morales
Join Date: Aug 2009
Posts: 24
Rep Power: 7
bbmorales is on a distinguished road
Hi there.

I am running a gas-solid euler-euler transient simulation in Fluent 14.
I am using the granular model. The transient formulation is the first order implicit.

I would like to use adaptive timesteps, but I cannot select it under the Time Stepping Method scroll list. It only has the fixed time step option available.

How can I do it?

I have found the following info in the manual:

Important:
Adaptive time stepping is available only with the pressure-based and density-based implicit formulations; it cannot be used with the density-based explicit formulation. In addition, it cannot be used with the discrete phase model, second-order time integration, Euler-Euler multiphase models (Approaches to Multiphase Modeling in the Theory Guide), or user-defined scalars (User-Defined Scalar (UDS) Transport Equations).

Is there any way that I can set an UDF or something to adapt the time step?

Regards!
bbmorales is offline   Reply With Quote

Old   January 23, 2013, 10:58
Default
  #2
Senior Member
 
SSL
Join Date: Oct 2012
Posts: 227
Rep Power: 5
msaeedsadeghi is on a distinguished road
You can use DEFINE_DELTAT to adapt timestep in density-based mode.
bbmorales likes this.
msaeedsadeghi is offline   Reply With Quote

Old   January 24, 2013, 07:29
Default
  #3
vig
New Member
 
anonymous
Join Date: Jan 2011
Posts: 23
Rep Power: 6
vig is on a distinguished road
DEFINE_DELTAT could be used irrespective of the solver.
You could write your own time step controlling mechanism.
bbmorales likes this.
vig is offline   Reply With Quote

Old   January 24, 2013, 07:45
Default
  #4
New Member
 
Bayard Morales
Join Date: Aug 2009
Posts: 24
Rep Power: 7
bbmorales is on a distinguished road
Hi guys - thanks for your help.

I haven't tried to do what you told me, so I may sound a little grumpy, but I have found this in the Fluent UDF manual:

DEFINE_DELTAT is a general-purpose macro that you can use to control the size of the time step
during the solution of a transient problem. Note that this macro can be used only if Adaptive is selected from the Time Stepping Method drop-down list in the Run Calculation task page in ANSYS FLUENT

In my case, the Adaptative option is not available in the drop-down list.

Did you guys go to run Euler-euler transient with adaptive?

Thanks!
bbmorales is offline   Reply With Quote

Old   February 14, 2013, 06:08
Thumbs up
  #5
New Member
 
Bayard Morales
Join Date: Aug 2009
Posts: 24
Rep Power: 7
bbmorales is on a distinguished road
[SOLVED]

In short: I cannot use UDF to change the time-step in Euler-Euler, but using the journal, I can do something similar.

I have contacted the Ansys support and this was the answer.

------

If granular model does not allow for adaptive time stepping then you will not be able to use DEFINE_DELTAT. This is because the hook for this function is available only when we select adaptive time stepping.

Instead of UDF, you can use a jurnal file for this purpose. A jurnal file is a file which contains commands for Fluent. In journal file, you can put text menu interface (TUI) commands which tells Fluent to do some time steps and then change the time step size. You can find more details on TUI commands in ANSYS14 help guide at this location:

// User's Guide :: 2 // 3. Text User Interface (TUI) // 3.1. Text Menu System


For example if you want to run the case for 5 time steps using existing timestep size and then want to change the time steps size to 2e-3 sec, here are the commands:

*********************
solve dual-time-iterate 5 10
solve set time-step 2e-3
***********************
You can put these two commands in a file with extension as jou and read it in Fluent from File->read -> journal
bbmorales is offline   Reply With Quote

Reply

Tags
adaptive-time stepping, time step

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
mesh size in Eulerian multiphase flow - liquid/solid mixture microfin FLUENT 3 June 10, 2014 12:53
questions about sensitivity analysis and adaptive timestep sjtusyc CFX 10 June 21, 2012 09:24
ANSYS CFX Adaptive Timestep aeroman CFX 8 July 25, 2009 06:37
Backflow in eulerian multiphase simulation xeusater FLUENT 0 June 26, 2009 07:50
multiphase Eulerian particles Zbynek CFX 5 September 24, 2008 11:21


All times are GMT -4. The time now is 11:00.