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

Capillary forces in Comet

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 24, 2004, 19:24
Default Capillary forces in Comet
  #1
Derek Coon
Guest
 
Posts: n/a
I recently tested a simple free surface problem in Comet - rise of water between two plates by capillary force and the code gave an error of about 10%. (The plate distance was 1 mm and the contact angle 45.) Does anyone have any suggestions as to why this may have occured? So far tech support hasn't been able to solve the problem.
  Reply With Quote

Old   August 25, 2004, 08:49
Default Re: Capillary forces in Comet
  #2
4xF
Guest
 
Posts: n/a
On what is the error based with this simple test case? 10% is the error on what? Could you be more explicite?
  Reply With Quote

Old   August 25, 2004, 11:02
Default Re: Capillary forces in Comet
  #3
Derek Coon
Guest
 
Posts: n/a
With a 45 contact angle and a surface tension of 0.07275 N/m water should rise 10.5 mm up between the plates. The best I am getting with Comet is a rise of 9.625 mm and the interface line between the air and water is very diffuse, over 40 cells between 0 and 1 concentrations. (I had to use a cell density of 32 cells/mm to get an answer even this accurate.) Note that using the same conditions with StarCD I get the correct answer of 10.5 mm with a tight air/water interface.
  Reply With Quote

Old   August 26, 2004, 05:07
Default Re: Capillary forces in Comet
  #4
4xF
Guest
 
Posts: n/a
It sounds to me that you are running a free-surface flow without using the HRIC scheme. What kind of discretisation scheme do you use and with which blending factor? Does it happen that you are running a too big a time-step? Remember that STAR-CD does subcycles if the time step is too large. Finally, 32 cells in the gap is a minimum, if the cells are equidistant. You have to capture the high gradients of concentration at the wall.
  Reply With Quote

Old   August 26, 2004, 11:19
Default Re: Capillary forces in Comet
  #5
Derek Coon
Guest
 
Posts: n/a
I tried cd, ud and hric. Blending was kept at 1.0. I am using a time step of 1e-4 sec with 50 inner iterations. If >32 cells per mm are required then Comet is unusable for my real model as it is a complex 3D geometry of about 11,000 mm3.
  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
Capillary forces at low contact angles Terje CFX 5 September 3, 2008 04:21
capillary Mauricio Schneebeli CFX 0 February 28, 2006 08:34
fidap capillary Andreas FLUENT 0 January 31, 2003 09:45
Filling by capillary forces Jochen Main CFD Forum 0 November 4, 2002 05:00
Filling by capillary forces Jochen FLUENT 0 November 4, 2002 04:57


All times are GMT -4. The time now is 06:20.