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

Hold up in a closed vessel

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 4, 2003, 16:54
Default Hold up in a closed vessel
  #1
Pascale Fonteijn
Guest
 
Posts: n/a
Hi all,

I am simulating (steady state and transient) the flow in a closed vessel, meaning that there are neither inlets nor outlets. The initial total amount of mass (hold up) is set by the reference pressure and the initial guess for the pressure. During the simulation the hold up is far from constant. Mass does not seem to be conserved in CFX 5.5.1/5.6!!!!!! Does any one no why? How can I fix this problem?

Pascale
  Reply With Quote

Old   June 4, 2003, 18:48
Default Re: Hold up in a closed vessel
  #2
Robin
Guest
 
Posts: n/a
Hi Pascale,

How many coefficient loops are you taking per timestep, and is the solver converging to you linear solver target?

Regards, Robin
  Reply With Quote

Old   June 5, 2003, 06:56
Default Re: Hold up in a closed vessel
  #3
Nyatoto
Guest
 
Posts: n/a
If you check my earlier posting, ( http://www.cfd-online.com/Forum/cfx.cgi?read=4987 ) you will notice some similrities. In the initial system (of that posting) I managed to solve the problem. I have not yet succeded in a different system i am dealing with presently. However, the starting point is what Robin has mentioned.

Regards Nyatoto
  Reply With Quote

Old   June 8, 2003, 18:31
Default Re: Hold up in a closed vessel
  #4
Pascale Fonteijn
Guest
 
Posts: n/a
- 3 loops

- after the first five time steps, the residuals fall down to approx 1e-5. Isn't that sufficient?

Pascale

  Reply With Quote

Old   June 9, 2003, 13:27
Default Re: Hold up in a closed vessel
  #5
Robin
Guest
 
Posts: n/a
Pascale,

The inner loop residual should be at least a MAX of 1e-3. You should require 3 to 5 coefficient loops to get to this level (note that this is not the same as the outer loop residual). I will typically allow the solver to use up to 7 inner loops and then adjust my timestep so it only uses 3 to 5 of them. If you are using all seven, you know the linear solver is not converging sufficiently.

The code does not explicitely conserve volume fraction. There is a beta parameter in CFX-5.6 which will do this, although it is really intended for steady state calculations. With a transient simulation you should be conserving the volume fraction anyway, if you are converging at each timestep. For the beta parameter, contact your local technical support.

Regards, Robin
  Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Boussinesq approximation in closed system Nitesh FLUENT 11 January 13, 2014 23:21
Gas filling in closed vessel chanfire CFX 3 February 16, 2010 18:23
How to simulate a closed two phase stirring vessel Jo CFX 1 November 12, 2007 17:29
Pressure Vessel Carlos V. FLUENT 0 June 4, 2006 21:44
Solid particles in a rotating vessel with 5.7.1 Sandeep CFX 0 May 17, 2005 11:54


All times are GMT -4. The time now is 19:38.