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

PPE in Projection Method

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 28, 2003, 11:12
Default PPE in Projection Method
  #1
Woo Tae Kim
Guest
 
Posts: n/a
Hello! I am solving the incompressible flows (vortex spin-off or lid-driven cavity in square geometry) using the prejection method. I cannot project out the divergence generating component of velocity field. (Just in the first time step) I am guessing that the problem is coming from the PPE. Laplacian(P) = Div(u)/dt For the vortex spin-off problem, the initial velocity field is given as u=0.25(y-0.5), v=0.25(0.5-x) and u=v=0 at the four boundaries (x=0,x=1,y=0,y=1). From these initial conditions, Div(u) is not zero near the boundaries but total sum of Div(u) over the entire domain is zero. I enforced the homogeneous Neumann BC for PPE at all boundaries but I cannot get a pressure field which has zero gradient at the boundary. Non-zero pressure gradient generate non-zero velocity component at the boundaries. Of course, I can reset these non-zero velocities by applying zero velocities at the boundaries. Does this non-zero pressure gradient arise from the source terms Div(u) at the boundaries or am I missing something?

How can I get rid of this problem? If you have some experience about this kind problem, please help me.

Regards,

Woo Tae

ps) Collocated variables arrangement is used in my code.
  Reply With Quote

Old   June 29, 2003, 00:20
Default Re: PPE in Projection Method
  #2
versi
Guest
 
Posts: n/a
Collocated variables arrangement is a bad,yet ? choice for projection method. The Poission eq. generally comes from discrete DIV & Grad. In staggered grid, there is no need for preesure BC. In Colocated grids, the resulting Possion eq. has multiple solutions, or even-odd point decoupling. One must specially treat this. If the Possion eq. comes from applying differential Div to momentum eq, this will need compactbility condition. You pressure Possion as well as its BC must consider this. There are lots of papers dealing with colocated grid for projection method.
  Reply With Quote

Old   June 29, 2003, 02:46
Default Re: PPE in Projection Method
  #3
Woo Tae Kim
Guest
 
Posts: n/a
Thank you for your kind comments. Could you reference some papers dealing with colocated grid for projection method?
  Reply With Quote

Reply


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
projection method for helical pipe(3D) ehsan_am86 Main CFD Forum 0 August 14, 2010 22:30
FDM projection method for steady-state ma Main CFD Forum 2 October 17, 2005 15:57
Multiphase Flow with Chorin's Projection Method Stefan Leschka Main CFD Forum 2 August 20, 2002 16:46
Projection method and Block-off method Leo Main CFD Forum 0 June 14, 2001 08:22
A Second-Order Projection Method for Incompressibl Ivan Main CFD Forum 5 April 29, 2001 08:27


All times are GMT -4. The time now is 04:33.