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

Equations as boundary condition

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   December 11, 2018, 15:17
Default Equations as boundary condition
  #1
Senior Member
 
Join Date: Jan 2013
Posts: 134
Rep Power: 11
kkpal is on a distinguished road
Hi, I'm wondering if it is possible to specify the boundary condition as a set of equations rather than specific variable.

I've trying to solve the potential flow with an unusual boundary condition dP/dn=f, in which P is the potential, n is the surface normal and f is an explicit variable. I know that in potentialFoam, the boundary condition enters by specifying velocity. By definition of potential flow we have dP/dx=Ux, dP/dy=Uy. Thus, the boundary condition breaks down to Ux*nx+Uy*ny=f, in which nx and ny are the two components of the surface normal vector.

How should I set the this kind of boundary condition?
kkpal is offline   Reply With Quote

Old   December 11, 2018, 23:09
Default
  #2
Senior Member
 
Join Date: Jan 2013
Posts: 134
Rep Power: 11
kkpal is on a distinguished road
I think this kind of boundary is very similar to the slip boundary, in which Ux*nx+Uy*ny=0 is ensured for the no-penetration condition. I wonder how openfoam implement such kind of boundary condition, in which the components of the velocity vector form an equation rather than appearing as explicit values.
kkpal is offline   Reply With Quote

Old   December 12, 2018, 23:13
Default
  #3
Senior Member
 
Join Date: Jan 2013
Posts: 134
Rep Power: 11
kkpal is on a distinguished road
After a few's days search I found surfaceNormalFixedValue may suit my needs.
kkpal is offline   Reply With Quote

Old   December 13, 2018, 14:24
Default
  #4
Senior Member
 
Join Date: Jan 2013
Posts: 134
Rep Power: 11
kkpal is on a distinguished road
I'm testing flow around a cylinder with both slip boundary condition and surfaceNormalFixedValue with refValue=0 on the cylinder wall. I suppose these two conditions are equivalent. However, I'm getting totally different results.
For the slip, I get a stable flow (left figure), while for the surfaceNormalFixedValue I get periodic shedding (right figure).

I'm wondering why is this happening.
Attached Images
File Type: jpg huayi.jpg (38.1 KB, 16 views)
File Type: jpg normal.jpg (45.6 KB, 17 views)
kkpal is offline   Reply With Quote

Reply

Tags
boundary condition, potential flow

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
Radiation in semi-transparent media with surface-to-surface model? mpeppels CFX 11 August 22, 2019 07:30
CFD analaysis of Pelton turbine amodpanthee CFX 31 April 19, 2018 18:02
mixed inflow/outflow downstream boundary condition question peob OpenFOAM Running, Solving & CFD 3 February 3, 2017 10:54
Out File does not show Imbalance in % Mmaragann CFX 5 January 20, 2017 10:20
Wrong flow in ratating domain problem Sanyo CFX 17 August 15, 2015 06:20


All times are GMT -4. The time now is 17:52.