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

Low-Pressure Boundary Slip

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

Like Tree1Likes
  • 1 Post By LuckyTran

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 4, 2018, 10:14
Default Low-Pressure Boundary Slip
  #1
New Member
 
Ziga
Join Date: Feb 2016
Location: Maribor, Slovenia
Posts: 27
Rep Power: 7
Zigec is on a distinguished road
Send a message via Skype™ to Zigec
Hey,

I looked through the forum and this boundary condition from fluent came a few times up, but there has never been a full answer on this topic.

First. It's clear, that for using this BC, one needs to have a pressure-based solver, the energy equation needs to be enabled and the laminar flow has to be selected. At this point you get under Options the LPBS choice.

So far, everything after the documentation. But what after this? When I go in the wall boundary tab, I have the same options, as when i don't enable LPBS: No-Slip, specify shear (free slip) and Marangoni stress, of course in addition to Stationary and Moving wall.

I tried a few simulations with different settings at this point, but I wasn't able to perform a slip.

Can someone help at this point?

Regarding my case. I have a mixture of water-vapor and air at -35C and 4Pa. The channel is around 20 mm in diameter.

Regards,
Ziga

Last edited by Zigec; April 4, 2018 at 11:26.
Zigec is offline   Reply With Quote

Old   April 4, 2018, 17:04
Default
  #2
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 4,119
Rep Power: 50
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
I see your confusion.

Quote:
Originally Posted by Zigec View Post
First. It's clear, that for using this BC, one needs to have a pressure-based solver, the energy equation needs to be enabled and the laminar flow has to be selected. At this point you get under Options the LPBS choice.
After you make it through this part. What you need to do is go to material properties and there you can specify the Leonnard-Jones parameters and the coefficients for the LPBS condition.

It only makes sense to use the LPBS with a no-slip wall, because if the wall was free-slip then there would be no need to activate the LPBS condition. When the shear is specified, the fluid does not care what is the wall velocity. This explanation unfortunately is not in the documentation.
LuckyTran is offline   Reply With Quote

Old   April 4, 2018, 17:07
Default
  #3
New Member
 
Ziga
Join Date: Feb 2016
Location: Maribor, Slovenia
Posts: 27
Rep Power: 7
Zigec is on a distinguished road
Send a message via Skype™ to Zigec
Thanks for the quick replay!

One more question. In case, that the Kn is not in the appropriate range for the slip flow, can it happen that the slip doesn't appear?

I just want to check every possible case, that i don't write on the forum 10 times
Zigec is offline   Reply With Quote

Old   April 4, 2018, 17:39
Default
  #4
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 4,119
Rep Power: 50
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
Honestly I am not sure. As far as I know, there is no low Kn or high Kn cut-off for when the LPBS model is applied. The full-slip and no-slip conditions are asymptotes of this model (so there should always some slip). But one would have to verify it.
Zigec likes this.
LuckyTran is offline   Reply With Quote

Old   January 8, 2021, 04:13
Default
  #5
New Member
 
zhangdongjie
Join Date: Jan 2021
Posts: 22
Rep Power: 2
zhangdongjie is on a distinguished road
Quote:
Originally Posted by LuckyTran View Post
I see your confusion.



After you make it through this part. What you need to do is go to material properties and there you can specify the Leonnard-Jones parameters and the coefficients for the LPBS condition.

It only makes sense to use the LPBS with a no-slip wall, because if the wall was free-slip then there would be no need to activate the LPBS condition. When the shear is specified, the fluid does not care what is the wall velocity. This explanation unfortunately is not in the documentation.
2D how to open low pressure boundary slip?
zhangdongjie is offline   Reply With Quote

Old   January 8, 2021, 06:40
Default
  #6
New Member
 
zhangdongjie
Join Date: Jan 2021
Posts: 22
Rep Power: 2
zhangdongjie is on a distinguished road
Quote:
Originally Posted by Zigec View Post
Hey,

I looked through the forum and this boundary condition from fluent came a few times up, but there has never been a full answer on this topic.

First. It's clear, that for using this BC, one needs to have a pressure-based solver, the energy equation needs to be enabled and the laminar flow has to be selected. At this point you get under Options the LPBS choice.

So far, everything after the documentation. But what after this? When I go in the wall boundary tab, I have the same options, as when i don't enable LPBS: No-Slip, specify shear (free slip) and Marangoni stress, of course in addition to Stationary and Moving wall.

I tried a few simulations with different settings at this point, but I wasn't able to perform a slip.

Can someone help at this point?

Regarding my case. I have a mixture of water-vapor and air at -35C and 4Pa. The channel is around 20 mm in diameter.

Regards,
Ziga
Low pressure boundary slip only works in 3D. How can I open this button in 2D?
zhangdongjie is offline   Reply With Quote

Reply

Tags
boundary, fluent, low-pressure, slip

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
CFD analaysis of Pelton turbine amodpanthee CFX 31 April 19, 2018 18:02
sliding mesh problem in CFX Saima CFX 45 September 22, 2015 10:53
Problem with SIMPLEC-like finite volume channel flow boundary conditions ghobold Main CFD Forum 3 June 15, 2015 11:14
replacing of shock tube high pressure part with a boundary condition for low pressure immortality Main CFD Forum 0 May 2, 2013 13:30
Water subcooled boiling Attesz CFX 7 January 5, 2013 03:32


All times are GMT -4. The time now is 15:03.