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

pressure oscillations

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 27, 2000, 06:21
Default pressure oscillations
  #1
nadeem hasan
Guest
 
Posts: n/a
I have developed an incompressible viscous flow solver based on an explicit finite difference scheme on a colocated grid. The scheme is first order accurate in time and second order accurate in space.(second order upwinding for convective terms and central for viscous terms). Before advancing the velocity field in time, the pressure field is corrected in order to enforce continuity at the new time level. This is done through the usual pressure poisson eqn formed by taking divergence of the discretised momentum equations.(Computational methods for fluid dynamics-Ferziger & Peric,pp 160-161).The problem that i am facing is that when i am testing the scheme for 2D lid driven cavity problem at Re=1000 and Re=10000 i am getting pressure oscillations in space while the results for the stream function and velocity profiles are in good agreement with reported data. Could you help me locate the problem.
  Reply With Quote

Old   June 27, 2000, 08:13
Default Re: pressure oscillations
  #2
John C. Chien
Guest
 
Posts: n/a
(1). It simply say that, cfd solution to Navier-Stokes equations ,especially for high Reynolds number problems, is still a research field. (2). Even for such seemingly simple 2-D lid driven cavity flow problem, the solution is still hard to come by. (3). Try the existing and working methods first. When you start inventing your method or following methods on a book (just review of methods), you are on your own.
  Reply With Quote

Old   June 27, 2000, 12:13
Default Re: pressure oscillations
  #3
Kalyan
Guest
 
Posts: n/a
The pressure oscillations with a checker board type spatial pattern are not uncommon in most flow solver, especially in incompressible flows.

The problem comes primarily due to the point-wise decoupling of velocity and pressure, i.e., the velocity update depends on the gradient of pressure and the (Laplacian of) pressure at a point depends on the velocity gradients at that point. So, the velocity at a point is insensitive to the pressure at the point.

The spatial grid can be divided into two different set of alternate grid points like the squares on chess board. The pressure at black points depends only on the velocity at the white points and the velocity at black points depends on the pressure at white points (and vice-versa). Hence, your velocity solution is perhaps smooth even if you have an oscillatory pressure. Standard ways of overcoming this problem are discussed in some detail in this paper.

@article{Zang_94, author = {Zang, Y. and Street, R. L. and Koseff, J. R.}, year = 1994, title = {A non-staggered grid, fractional step method for time dependent incompressible Navier-Stokes equations in curvilinear coordinates}, journal = {Journal of Computational Physics}, volume = 114, number = 1, pages = {18--33}

Good luck.

  Reply With Quote

Reply

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Fluent natural ventilation pressure boundary condition pierresandre FLUENT 24 November 8, 2011 15:32
UDF to define or adjust pressure??? engahmed FLUENT 0 July 6, 2010 17:19
Neumann pressure BC and velocity field Antech Main CFD Forum 0 April 25, 2006 02:15
Pressure oscillations Anton Lyaskin CD-adapco 0 April 30, 2002 03:33
Hydrostatic pressure in 2-phase flow modeling (long) DS & HB Main CFD Forum 0 January 8, 2000 16:00


All times are GMT -4. The time now is 13:24.