CFD Online URL
[Sponsors]
Home > Forums > CFX

Free surface modelling under CFX 4

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

Reply
 
LinkBack Thread Tools Display Modes
Old   April 18, 2002, 23:12
Default Free surface modelling under CFX 4
  #1
Dahong
Guest
 
Posts: n/a
Hi, everyone!

I am trying to simulate an air-water two phases flow for obtaining the location of the free surface by using CFX 4. I set two inlets for the solution domain, one is air inlet and another is water inlet. I also set an outlet for the solution domain.

I have specified the BC's at the inlets as follows: i) for air inlet: air velocity is 1.0m/s, air volume fraction is 1; water velocity is 1.0m/s, water volume fraction is 0 ii) for water inlet: air velocity is 1.0m/s, air volume fraction is 0; water velocity is 1.0m/s, water volume fraction is 1 The default option is used for the outlet.

I also set the initial volume fraction VFRAC(INODE,IPHASE) within the solution domain by using the User-Subroutine USRINT, and use the homogeneous model to simulate the free surface between the air and the water.

I run the calculation for some iterations for test and can see the free surface under the Post-processor. The problem is that no free surface is found after the running of 2000 iterations. I don't know why?

Please help me! Thanks in advance.

  Reply With Quote

Old   June 20, 2002, 07:52
Default Re: Free surface modelling under CFX 4
  #2
Prash
Guest
 
Posts: n/a
hi could you please tell me whether you are running the simulation in transient or a steady state. free surface modelling using surface tension model and the surface sharpening algorithm works only for transient models. there could be many reasons why you are not able to see the free surface.... 1. it could be a convergence issue ... volume fraction in the entire domain is 0.5.. and you dont get any interface... this is probably due to your boundary conditions. 2. it could be that the timesteps you have specified are too large for the convergence to be achieved... hope this helps... cheers prash
  Reply With Quote

Old   June 23, 2002, 00:07
Default Re: Free surface modelling under CFX 4
  #3
Dahong
Guest
 
Posts: n/a
Hi Prash, Thank you for your help. I run the calculation in the transient state. As a first try, even the turbulence model is not included. The time step used is 0.5. Do you think the time step must be smaller than that? I have checked that the setting of initial fraction should be OK, I can still see the free surface in few time steps. It seems to be somewhere wrong during setting the model, but I can not fix it.
  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
Can Flow-3D plot the free surface area in Iso-surface or colour variable? therockyy FLOW-3D 1 June 20, 2010 20:36
CFX gravity driven free surface flow tutorial mechovator CFX 37 July 27, 2009 11:28
Free Surface Modelling and Reversed Flow Error Javier González FLUENT 4 August 16, 2004 12:37
cfx free surface nico CFX 0 July 7, 2004 08:43
BC for free surface pilar FLUENT 3 January 14, 2004 08:36


All times are GMT -4. The time now is 11:09.