CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

boundary condition of an internal surface

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 29, 2011, 21:16
Default boundary condition of an internal surface
  #1
New Member
 
Join Date: May 2010
Posts: 7
Rep Power: 0
ynsudo is on a distinguished road
Dear all,

I would like to calculate mass flow rate of a small surface put in flow. The surface is put just for calculating flow rate so it should not affect the flow.

The solver I use is interFoam. I wonder if I have to define the small surface as a patch and pose boundary condition of gradient zero for pressure, velocity, and volume fraction or there is other better ways. Iíd be glad if you give me advice.
Thank you in advance for your help.

Yu
ynsudo is offline   Reply With Quote

Old   June 30, 2011, 09:23
Default
  #2
New Member
 
Join Date: Jun 2011
Location: Rotterdam, the Netherlands
Posts: 9
Rep Power: 7
Van de Leur is on a distinguished road
Dear Yu,

Sampling data is explained in paragraph 6.5 of the OF user guide.
You can take samples anywhere in your domain without defining a surface, just create a file called sampleDict.

Regards,

Kevin
Van de Leur is offline   Reply With Quote

Old   June 30, 2011, 21:59
Default
  #3
New Member
 
Join Date: May 2010
Posts: 7
Rep Power: 0
ynsudo is on a distinguished road
Dear Kevin,

Thank you for your advice. Itís great that if I donít have to specify patch for my purpose since I donít have to think about boundary condition that doesnít affect the flow.



I have a question about the sampleDict.
According to the paragraph 6.5 of the OF user guide, it seems that I could choose keyword "surfaces" in the sampleDict.
http://www.openfoam.com/docs/user/sa...hp#x34-2001106



The shape of a surface where I want to calculate flow rate is an ellipse so I want to know how to calculate flow rate on surface with any shape. I think it can be specified by the STL file. I am wondering if that is possible in sampleDict. Or if there is any other way to solve my problem and teach me it would be appreciated.

Best regards,
Yu
ynsudo is offline   Reply With Quote

Old   July 4, 2011, 03:51
Default
  #4
New Member
 
Join Date: Jun 2011
Location: Rotterdam, the Netherlands
Posts: 9
Rep Power: 7
Van de Leur is on a distinguished road
You could create a surface/patch to take samples. This is certainly possible for boundary patches but I'm not sure how it works with patches in the middle of a domain.

Another way is to use the 'cloud' option in the sampleDict and specify the coordinates of the points (on your ellipse) you want to sample.

Regards,

Kevin
Van de Leur is offline   Reply With Quote

Old   July 4, 2011, 05:55
Default
  #5
New Member
 
Join Date: May 2010
Posts: 7
Rep Power: 0
ynsudo is on a distinguished road
Hello Kevin,
Thank you for your reply. It is very helpful.

About the first way you mentioned Iím not sure but it seems that I have to define boundary patches so I need to think about proper boundary conditions that donít affect flow around the patch.

The second way seems to work. For example, I may need a STL file for the shape such as an ellipse, then get the area and the coordinates of a triangle consisting of the STL, then get velocity for the coordinate by sampleDict with Ďcloudí option, then calculate flow rate by multiplying the velocity by the area for a triangle and summing up them. I may need to make a program to calculate it.

Yu
ynsudo is offline   Reply With Quote

Old   September 13, 2011, 09:52
Default
  #6
Member
 
Miles
Join Date: Sep 2011
Posts: 48
Rep Power: 7
miles_davis is on a distinguished road
hi ynsudo,

I have the same problem: I want to have the flow rate throug a given surface. The surface is already defined in my mesh so it would be a boundary patch or a cyclic patch.
What I do not uynderstand when I look at the SampleDict example in the Userguide is how to find the syntaxe for programming the flow rate through each face of the patch surface and then sum it over all the faces of the surface patch. surface
Any help would be welcomed.

Thanks
miles_davis is offline   Reply With Quote

Old   September 13, 2011, 20:37
Default
  #7
New Member
 
Join Date: May 2010
Posts: 7
Rep Power: 0
ynsudo is on a distinguished road
Hello Miles

I am trying to use a routine named calcMassFlow to calculate the mass flow rate.
http://openfoamwiki.net/index.php/Contrib_calcMassFlow
There would be a program for higher versions.
This routine could calculate the mass flow rate for one-phase flow.
If you would like to calculate the mass flow rate for two-phase flow you would need to modify the program.
Best,
Yu
ynsudo is offline   Reply With Quote

Old   September 14, 2011, 04:17
Default
  #8
Member
 
Miles
Join Date: Sep 2011
Posts: 48
Rep Power: 7
miles_davis is on a distinguished road
Thanks you
I am gonna check this... as soon as I have found a good programming tuto on openfoam.
miles_davis is offline   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
Surface with double boundary condition Marcopolopeich CFX 2 January 16, 2011 11:41
asking for Boundary condition in FLUENT Destry FLUENT 0 July 27, 2010 00:55
External Radiation Boundary Condition for Grid Interface CFD XUE FLUENT 0 July 9, 2010 02:53
External Radiation Boundary Condition (Two sided wall), Grid Interface CFD XUE FLUENT 0 July 8, 2010 06:49
The Boundary Condition about the Flat Plate boing Main CFD Forum 1 January 6, 2002 17:53


All times are GMT -4. The time now is 18:04.