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

Slip boundary condition giving strange results

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 17, 2007, 10:24
Default Hi! I am currently modeling
  #1
Senior Member
 
Rasmus Hemph
Join Date: Mar 2009
Location: Sweden
Posts: 108
Rep Power: 17
hemph is on a distinguished road
Hi!
I am currently modeling two-phase flow using the twoPhaseEulerFoam-application. As a boundary condition for the velocity of the dispersed phase at the outlet, I set the slip-condition. From the user manual, this boundary condition should limit the velocity normal to the face to 0, and the tangential velocity to zero gradient.

However, I get an outflow of particles/dispersed phase through this boundary!

(snip from the output log at successive time steps)
Dispersed phase volume fraction = 0.0327019 Min(alpha) = -2.2858e-31 Max(alpha) = 0.237186
Dispersed phase volume fraction = 0.0327019 Min(alpha) = -6.25311e-33 Max(alpha) = 0.237186
Dispersed phase volume fraction = 0.0326999 Min(alpha) = -2.19122e-31 Max(alpha) = 0.237179
Dispersed phase volume fraction = 0.0326999 Min(alpha) = -5.10842e-33 Max(alpha) = 0.237179
Dispersed phase volume fraction = 0.032698 Min(alpha) = -2.10048e-31 Max(alpha) = 0.237171
(/snip)

The flux of phia is of non-zero.

(example from phia-output file)
outlet
{
type calculated;
value nonuniform List<scalar>
12
(
2.93748e-10
3.68239e-10
4.54842e-10
5.29354e-10
5.82653e-10
6.10416e-10
6.10416e-10
5.82653e-10
5.29354e-10
4.54842e-10
3.68239e-10
2.93748e-10
)


It is important to the simulation that the particles stay within the domain! Am I misunderstanding something about the slip boundary condition?

Best Regards
Rasmus H
hemph is offline   Reply With Quote

Old   January 17, 2007, 20:13
Default Hi Rasmus, Wanna post your
  #2
Senior Member
 
Join Date: Mar 2009
Location: My oyster
Posts: 124
Rep Power: 17
ziad is on a distinguished road
Hi Rasmus,

Wanna post your configuration files and maybe your mesh?

cheers,
Ziad
ziad is offline   Reply With Quote

Old   January 18, 2007, 04:22
Default Hi Rasmus I have been playi
  #3
New Member
 
Joakim Möller
Join Date: Mar 2009
Posts: 26
Rep Power: 17
joakim is on a distinguished road
Hi Rasmus

I have been playing along with interFoam using both the slip and the symmetry condition (in 2D). In both cases I get convergence problems, with pressure oscillations along the surface, whereas when I change he b.c. to a wall condition, everything works fine.

Has anybody else had any equal experiences?

Regards

/Joakim
joakim is offline   Reply With Quote

Old   January 18, 2007, 05:15
Default Hi, I did a bit more investig
  #4
Senior Member
 
Rasmus Hemph
Join Date: Mar 2009
Location: Sweden
Posts: 108
Rep Power: 17
hemph is on a distinguished road
Hi,
I did a bit more investigation. The slip condition does actually set the outward velocity Ua to zero for the dispersed phase. The problem is that the corresponding flux field phia does not know about this.. For the case where the boundary condition is derived from fixedValue, phia is updated correspondingly in phaseModel/phaseModel.C.

In the present case of a slip boundary condition, this update is not performed, and phia and Ua are not strictly coupled. I added a test for slip b.c. to phaseModel.C as:

if
(
isType<fixedvaluefvpatchvectorfield>(U_.boundaryFi eld()[i]) ||
(U_.boundaryField()[i].type() == "slip") )
{
phiTypes[i] = fixedValueFvPatchScalarField::typeName;
}

which seems to do the trick. This might have other implications which I am not aware of. Generally, care needs to be taken to boundary conditions which are not fixed value, but should stop one of the phases.
hemph is offline   Reply With Quote

Reply

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
SLIP BOUNDARY CONDITION vas FLUENT 12 June 27, 2019 05:48
Non-slip Boundary condition A.T. Main CFD Forum 7 November 28, 2012 03:19
RasInterFoam STRANGE RESULTS AT BOUNDARY kumar2 OpenFOAM Running, Solving & CFD 8 March 24, 2008 18:38
"Slip Boundary Condition,Help me Please" Sohag CFX 1 June 21, 2007 06:34
strange things happen with slip boundary lei wang FLUENT 0 May 16, 2007 22:47


All times are GMT -4. The time now is 23:46.