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

pressure boundary condition on the wall

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   December 19, 2003, 01:28
Default pressure boundary condition on the wall
  #1
fluideniro
Guest
 
Posts: n/a
I have a problem unsolved till now. I study the flow around a square cylinder by using SIMPLER method. I had to deal with the pressure boundary condition on the wall of the square cylinder because I define the grid node on the wall. As you know, the four corners of the cylinder are special nodes in this problem. Does anybody know how to give the pressure condition on the wall especially on the corners? please give me your advice! Thank you for any help you can give me!
  Reply With Quote

Old   December 19, 2003, 04:55
Default Re: pressure boundary condition on the wall
  #2
Praveen
Guest
 
Posts: n/a
You can use normal momentum equation

dp/dn = ρ n.u.∇u

where n is unit normal vector. But at a corner there is no unique normal. Mathematically pde does not make sense at such corners. The correct equations to use would be integral equations which are statements of conservation but have to be applied to a control volume.

In your case you will have to use some tricks which cannot be fully justified in terms of the governing equations. The simplest option is to just interpolate the pressure from the surrounding nodes. Or you could apply the normal momentum equation using an average normal taken from the two sides of the corner. Generally such tricks work.
  Reply With Quote

Old   December 19, 2003, 06:08
Default Re: pressure boundary condition on the wall
  #3
Tom
Guest
 
Posts: n/a
If I remember correctly the pressure in the corner is singular and so your finite difference approximation will be badly in error here - I think it was D.W. Moore did some work on this. What he did was subtract the singularity off and then solve for the smooth bit. (It's the singularity which creates the Moffat eddies near the corner).

Tom.
  Reply With Quote

Old   December 20, 2003, 07:55
Default Re: pressure boundary condition on the wall
  #4
kenn
Guest
 
Posts: n/a
if you use MAC staggered grid, how can you get a velocity nodes at corners? and how can you get a pressure nodes on wall boundaries?

the correct boundary conditions for pressure poisson equation is not the one believed by many, which is derived from normal component of momentum equation. it is simply "partial p partial n = 0"

essnetially, application of momentum equation on wall boundaries is an illegal but sometimes helpful operation.
  Reply With Quote

Old   December 22, 2003, 09:30
Default Re: pressure boundary condition on the wall
  #5
Praveen
Guest
 
Posts: n/a
I have to make some corrections to my previous post.
  1. There should be a negative sign on the right hand side.
  2. The equation I wrote is for inviscid flows.
  3. For viscous flows, we have dp/dn = n.∇.τ where τ is the shear stress tensor.

For some references see

Roger Peyret, Handbook of Computational Fluid Mechanics, Academic Press.

Check chapter 3.

In boundary layer theory we study that at high Reynolds numbers, when boundary layers are thin, the pressure gradient normal to the wall is zero. Obviously, this is not true in general.
  Reply With Quote

Old   December 22, 2003, 18:53
Default Re: pressure boundary condition on the wall
  #6
grad
Guest
 
Posts: n/a
One may wish to look at applied mechanics reviews aug 2003 :"On boundary conditions for incompressible Navier-stokes equation" by Dietmer Rempfer in this regard...this paper tells the truth that the bc to pressure poisson equation cannot be specified with local relationships at the boundary...

a guy with time energy money and proper training can implement Kleiser and Schumann's influence matrix method (proceedings of GAMM conference 1980) in a preprocessing step for BC...

in my opinion : "partial p partial n = 0" is fair (if we trust the schemes we are using)....

"That derived from from normal component of momentum equation" leads to 'ill-posed differential equation problem'

  Reply With Quote

Old   December 22, 2003, 18:56
Default Re: pressure boundary condition on the wall
  #7
grad
Guest
 
Posts: n/a
thanks...the idea about normals clarified a problem with boundary condition to electric field on the corners of a liquid-solid interface...
  Reply With Quote

Old   December 23, 2003, 01:28
Default BC for PPE is resolved.
  #8
kenn
Guest
 
Posts: n/a
boundary conditions for pressre poisson equations have been resolved. I would like to look at the paper on applied mechanics review, but just keep track of Journal of Computational Physics from 2005 papers.

basically, if you need boundary conditions for pressure poisson, then I always can find an alternative but similar method which does not need any numerical BC at all. tentatively, I name these methods as: exact factorization, approximate factorization, and variable splitting for indefinite system.

I am submitting the paper on ef, and will submit the af next month, and then variable splitting two months later; all to JCP.
  Reply With Quote

Old   December 23, 2003, 01:29
Default Re: pressure boundary condition on the wall
  #9
Praveen
Guest
 
Posts: n/a
I was unable to locate

applied mechanics reviews aug 2003 :"On boundary conditions for incompressible Navier-stokes equation" by Dietmer Rempfer

There is no issue in Aug 2003.
  Reply With Quote

Old   December 23, 2003, 23:38
Default Re: pressure boundary condition on the wall
  #10
fluideniro
Guest
 
Posts: n/a
In my case, the primitive variable method (SIMPLER scheme)and the stagged grid is used. The main nodes are set to the wall of the square cylinder. So on the wall, there are only pressure nodes.

In my opinion, the boundary conditions for pressure on the wall,which is derived from normal component of momentum equation, may not be "partial p partial n = 0" .Because another item of the equation--the second normal derivative of velocity is not equal to zero.

by the way, can you tell me how can I DOWNLOAD the paper you've said about the BC for PPE?

Thank you very much and Merry Christmas!

  Reply With Quote

Old   December 24, 2003, 00:55
Default Re: pressure boundary condition on the wall
  #11
grad
Guest
 
Posts: n/a
sorry...I have the manuscript of the paper the author submitted..... I can mail you the same(1103k)...
  Reply With Quote

Old   December 24, 2003, 00:58
Default Re: pressure boundary condition on the wall
  #12
Praveen
Guest
 
Posts: n/a
If you can mail it to me then that would be great. My id is

praveen[at]aero.iisc.ernet.in
  Reply With Quote

Old   December 24, 2003, 02:10
Default Re: pressure boundary condition on the wall
  #13
Apurva Shukla
Guest
 
Posts: n/a
can you mail the manuscript at :

apurvas@aero.iitb.ac.in

Thanks

Apurva
  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
Pressure boundary condition C-H Kuo Main CFD Forum 18 September 16, 2016 04:19
Pressure Inlet Boundary Condition Prasad FLUENT 6 April 9, 2013 22:32
pressure boundary condition in fractional step Jean-François Corbett Main CFD Forum 3 January 10, 2006 09:49
Please help with flow around car modelling! Tudor Miron CFX 17 March 19, 2004 20:23
Pressure boundary condition Luigi Scivoletto Main CFD Forum 3 September 28, 1999 17:37


All times are GMT -4. The time now is 04:08.