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

Why no-slip b.c. does not obtain zero-velocity contour?

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

Like Tree1Likes
  • 1 Post By Tobi

Reply
 
LinkBack Thread Tools Display Modes
Old   May 15, 2017, 13:14
Default Why no-slip b.c. does not obtain zero-velocity contour?
  #1
New Member
 
Ran
Join Date: Aug 2016
Posts: 19
Rep Power: 3
random_ran is on a distinguished road
Greeting O.F.er:

I have a question regarding with no-slip boundary condition.

The simulation case is really simple: flow over a circular cylinder. My confusion is that why velocity contour on the surface of the cylinder is not zero? Is that violate the no-slip b.c?

I am using pisoFoam with O.F. v4.1. ParaView is v5.2.0.

Can someone elaborate a little bit of it?

Thanks,

Ran



Q1.jpg
Q2.jpg
random_ran is offline   Reply With Quote

Old   May 16, 2017, 12:46
Default
  #2
Senior Member
 
Joachim Herb
Join Date: Sep 2010
Posts: 425
Rep Power: 13
jherb is on a distinguished road
You selected the point values of U to be displayed. What happens if you select the cell values (in the menu at the top select U with a box in front of it and not a point).
jherb is offline   Reply With Quote

Old   May 16, 2017, 16:20
Default
  #3
New Member
 
Ran
Join Date: Aug 2016
Posts: 19
Rep Power: 3
random_ran is on a distinguished road
Hi, jherb:

Thanks for your reply.

I have also checked the cell value, but it still gives me zero velocity contour on the surface of the cylinder. Is that something wrong with my understanding of the boundary condition? or it is a bug?

q22.jpg
q11.jpg

Last edited by random_ran; May 16, 2017 at 16:22. Reason: typo
random_ran is offline   Reply With Quote

Old   May 16, 2017, 18:03
Default
  #4
Super Moderator
 
Tobi's Avatar
 
Tobias Holzmann
Join Date: Oct 2010
Location: Leoben (Austria)
Posts: 1,963
Blog Entries: 6
Rep Power: 33
Tobi has a spectacular aura aboutTobi has a spectacular aura about
Send a message via ICQ to Tobi Send a message via Skype™ to Tobi
The problem should be related to the reader. You are using paraview and not paraFoam, right? So paraview cannot handle the BC. Either use paraFoam or check out the files in your time directories. If for the BC you have »noSlip« and no other value, you are fine and it is really just a problem with displaying the stuff.

A workaround is to rename noSlip to fixedValue. Maybe in the latest ParaView version they fixed it.
Maybe you also can load an empty file named *.OpenFOAM
venturi likes this.
__________________
Keep foaming,
Tobias Holzmann
Tobi is offline   Reply With Quote

Old   May 25, 2017, 08:49
Default
  #5
New Member
 
Wagner C. Galuppo
Join Date: Feb 2012
Location: Portugal
Posts: 10
Rep Power: 7
wagnergaluppo is on a distinguished road
Thanks for the answer

I also experienced that this is a dummy exhibit in ParaView. I tried to view the results with the paraFoam -builtin command usage, to check the solution while it was running, and I've got values for the velocity field on the wall. So when I reconstructed it and just checked the results with the paraFoam command, the velocity values for the wall were correct with value zero as expected for a wall with no slip condition. A figure is attached!

Best regards,
Wagner Galuppo

Screenshot from 2017-05-25 12-02-42.jpg
wagnergaluppo is offline   Reply With Quote

Old   September 13, 2017, 09:03
Default
  #6
New Member
 
Ben
Join Date: Oct 2016
Posts: 9
Rep Power: 3
bentkj is on a distinguished road
Quote:
Originally Posted by Tobi View Post
The problem should be related to the reader. You are using paraview and not paraFoam, right? So paraview cannot handle the BC. Either use paraFoam or check out the files in your time directories. If for the BC you have »noSlip« and no other value, you are fine and it is really just a problem with displaying the stuff.

A workaround is to rename noSlip to fixedValue. Maybe in the latest ParaView version they fixed it.
Maybe you also can load an empty file named *.OpenFOAM
But noSlip and fixedValue (0 0 0) really means the same thing right? i guess as long as we've ensured one or the other for our BC we should be fine?

EDIT: Yes, I've experimented a little and like Wagner mentioned, the problem lies with the .foam and .OpenFOAM format for paraview. As long as the noSlip condition is ensured as the BC, it should be alright.

Thanks!
Ben
bentkj is offline   Reply With Quote

Old   Yesterday, 16:30
Default
  #7
New Member
 
Ran
Join Date: Aug 2016
Posts: 19
Rep Power: 3
random_ran is on a distinguished road
Quote:
Originally Posted by Tobi View Post
The problem should be related to the reader. You are using paraview and not paraFoam, right? So paraview cannot handle the BC. Either use paraFoam or check out the files in your time directories. If for the BC you have »noSlip« and no other value, you are fine and it is really just a problem with displaying the stuff.

A workaround is to rename noSlip to fixedValue. Maybe in the latest ParaView version they fixed it.
Maybe you also can load an empty file named *.OpenFOAM

Thanks Tobi. Yes, I used ParaView instead of paraFoam. I did not fully understand how the ParaView really worked. ParaView helps us to read the data. I checked the raw data OpenFOAM calcuated for me. It only contains the value at cell center, which means that the other locations within the cell are interpreted from the the cell center data. ParaView must know the interpretation rule. In this thread, maybe I was incorrectly follow the rule, so I confused ParaView, which eventually caused ParaView to calcuate a non-zero velocity at the no-slip B.C..

Quote:
Originally Posted by wagnergaluppo View Post
Thanks for the answer

I also experienced that this is a dummy exhibit in ParaView. I tried to view the results with the paraFoam -builtin command usage, to check the solution while it was running, and I've got values for the velocity field on the wall. So when I reconstructed it and just checked the results with the paraFoam command, the velocity values for the wall were correct with value zero as expected for a wall with no slip condition. A figure is attached!

Best regards,
Wagner Galuppo

Attachment 56245
Hi Wagner,

From the provided information, paraFoam had the capacity to identify the no-slip B.C. and changed the interpretation rule at the cell whose faces are no-slip B.C.s. Thanks for your information.


Quote:
Originally Posted by bentkj View Post
But noSlip and fixedValue (0 0 0) really means the same thing right? i guess as long as we've ensured one or the other for our BC we should be fine?

EDIT: Yes, I've experimented a little and like Wagner mentioned, the problem lies with the .foam and .OpenFOAM format for paraview. As long as the noSlip condition is ensured as the BC, it should be alright.

Thanks!
Ben

Hi Ben:

Noslip is equal to fixedValue (0 0 0). They are the same thing. One is a jargon and the other is a mathmatical description.

I have tried the name trick, but it fails again (ParaView 5.4.0 64bit on Windows).

Thank you guys,

Last edited by random_ran; Today at 11:54.
random_ran 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
Difference in values of velocity contour and velocity vector dreamz FLUENT 5 February 22, 2017 07:43
VELOCITY vs VELOCITY IN STN FRAME vs RELATIVE VELOCITY everest20 FLUENT 1 July 13, 2015 08:35
Velocity contour at interfaces problem marauder FLUENT 1 March 26, 2015 10:01
Applying slip velocity whosays Fluent UDF and Scheme Programming 1 March 5, 2015 22:31
why boudary slip velocity is so larte using udf cxzhao FLUENT 0 July 4, 2005 00:06


All times are GMT -4. The time now is 21:07.