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

Discuss about computation time of FLUENT

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 22, 2007, 11:01
Default Discuss about computation time of FLUENT
  #1
Kelly
Guest
 
Posts: n/a
Hello,

I am simulating flow using FLUENT in a small scale rectangualer pond (only 2m*4.6m*2m).The computations are really so demanding and time consuming.1 second is computed in about 2-3 hours. I wonder is it applicable to use FLUENT in a long time simualtion such as a storm which may last for several hours or even a day. If so it will last for at least half a year to finish computation.

My Problem:

- 3D unsteady simulation, - VOF (air-water), - k-epsilon, - PISO, - pressure: Body Force Weighted, - default under-relaxation factors - mesh size=0.1 m.

Can you present here some of your experiences? Thanks,

Kelly
  Reply With Quote

Old   August 22, 2007, 11:20
Default Re: Discuss about computation time of FLUENT
  #2
Dusan
Guest
 
Posts: n/a
Hello Kelly,

I have the same problem but it is in 2D and I want to shake it, with pond. And your Courant number is OK?
  Reply With Quote

Old   August 22, 2007, 15:11
Default Re: Discuss about computation time of FLUENT
  #3
Kelly
Guest
 
Posts: n/a
Thanks,Dusan. My Courant number is 0.25.
  Reply With Quote

Old   August 22, 2007, 16:04
Default Re: Discuss about computation time of FLUENT
  #4
AAA
Guest
 
Posts: n/a
Hi

May I ask: 1)how many cells there are in the domain, 2)what is the time step size and number of time steps, 3)what computaional power do you have?

Regards

AAA
  Reply With Quote

Old   August 22, 2007, 16:26
Default Re: Discuss about computation time of FLUENT
  #5
Kelly
Guest
 
Posts: n/a
AAA,thanks for your attention! The problem have 97293 cells; time step size=0.001s (I tried bigger ones but failed to get convergence),number of time steps=5000.I am not sure about the computational setting of this lab computer but it should have at least 512mb RAM.

Kelly
  Reply With Quote

Old   August 23, 2007, 09:17
Default Re: Discuss about computation time of FLUENT
  #6
AAA
Guest
 
Posts: n/a
Hi

The total duration of your run is 5 seconds with 1000 steps per second. This is comutationally demanding. Have you obtained any satisfactory results yet? If yes, have it run over night. Otherwise, have less number of time steps, say 1000 (1 second scene) to see what happens. PISO gives me trouble sometimes too. Try using another scheme (SIMPLIC) and see if the calculations speed up. As for pressure discretization, I know that body force weighted is to be used here, but try using 2nd order. finally, consider lowering under-relaxation factors.

Good luck

AAA
  Reply With Quote

Old   August 23, 2007, 12:32
Default Re: Discuss about computation time of FLUENT
  #7
Kelly
Guest
 
Posts: n/a
Hi AAA,

I could get satisfactory results even though it is computationally demanding. Still I am thinking how to get over this long lasting computaion time. I tried as you suggested but failed: firstly there is a warning "turbulent viscosity limited to viscosity ratio****" and then ended with divergence after several iterations. I am trying to change UR factors to aviod this now. Hopefully it will work.

Thanks for your suggestion.

Kelly
  Reply With Quote

Old   August 24, 2007, 20:43
Default Re: Discuss about computation time of FLUENT
  #8
AAA
Guest
 
Posts: n/a
Hi Kelly

Let's take care of the warning "turbulent viscosity limited to viscosity ratio****" which is not physical. This problem is mainly due to one of the following:

1)Poor mesh quality(i.e.,skewness > 0.85 for Quad/Hex, or skewness > 0.9 for Tri/Tetra elements). {what values do you have?}

2)Use of improper turbulent boudary conditions.

3)Not supplying good initial values for turbulent quantities.

I hope this helps.

Regards

AAA

  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
Moving mesh Niklas Wikstrom (Wikstrom) OpenFOAM Running, Solving & CFD 122 June 15, 2014 06:20
Time to open Fluent from Workbench ResH FLUENT 0 September 30, 2010 02:11
PostChannel maka OpenFOAM Post-Processing 5 July 22, 2009 09:15
IcoFoam parallel woes msrinath80 OpenFOAM Running, Solving & CFD 9 July 22, 2007 02:58
Could anybody help me see this error and give help liugx212 OpenFOAM Running, Solving & CFD 3 January 4, 2006 19:07


All times are GMT -4. The time now is 13:16.