
[Sponsors] 
August 18, 2009, 01:07 
periodic boundary conditions

#1 
New Member
Ranjith
Join Date: Apr 2009
Posts: 4
Rep Power: 9 
Hi,
Iam trying to simulate one microorganism locomotion in a low reynolds number fluid using IBM.The microorganism is described as a sine wave.i applied periodic boundary conditions at the left and right for velocity and pressure and no gradient boundary condition at the top and bottom of the square computational domain.iam using SOR as the solver for velocity and pressure.My problem is the SOR solver for pressure is not converging because of periodic boundary condition.Can anyone suggest me how to overcome this.even i tried with by making average velocity to zero after every iteration.it also does not work.Reg.this i need help and suggestions from any one. Thanking you Sincerely, 

August 24, 2009, 12:11 

#2  
New Member
federico
Join Date: Aug 2009
Posts: 8
Rep Power: 8 
Quote:
How many cycle of SOR do you use? You need really a lot of iteration with just sor to have convergence, because sor dumps very well high frequency disturbance but not the low one, maybe you can add a multigrid solution to your sor. Then you say that you are using the IBM. Try to plot cell by cell your divergence, maybe it is not converging in your cell closed to the immersed surface. 

August 24, 2009, 18:49 

#3 
Member
M. Nabi
Join Date: Jun 2009
Posts: 44
Rep Power: 9 
SOR converges very slowly for pressure correction equation. I think, it is better to solve the pressure by Krylov space methods (like CG) or Multigrid.
If your boundary conditions for pressure are all Neuman and periodic, you will have a singular problem. to avoid this problem, you need to fix the pressure by a constant (i.e. zero) in one point. 

August 24, 2009, 23:03 

#4 
New Member
Ranjith
Join Date: Apr 2009
Posts: 4
Rep Power: 9 
Hi,
Thanks for your valuable suggestions.Actually I modified the same problem by applying periodic boundary conditions in X and Y directions for both pressure and velocity.Iam using uniform grid system.Still Iam facing the problem of SOR convergence for pressure.Also the continuity is not satisfying.I found that the the pressure and velocities are becoming high at the 4 corner points ofthe boundary.Iam wondering how it is happening?Because we have boundary conditions there.Near the Immersed boundary there is no problem......can anyone guess what is happening and how I can overcome this problem. 

August 24, 2009, 23:45 

#5  
New Member
federico
Join Date: Aug 2009
Posts: 8
Rep Power: 8 
Quote:
Which is the residual of your poisson solver? how many cycle are you using? if you use just sor you can require also several hundred of pressure cycle to obtain the solution 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
periodic boundary conditions fro pressure  Salem  Main CFD Forum  21  April 10, 2013 00:44 
Periodic Boundary Conditions for the Temperature  A. Alzoubi  CFX  0  November 30, 2007 15:55 
Urgent: periodic boundary conditions  ck1973  FLUENT  3  July 5, 2006 11:32 
How to apply a periodic boundary conditions  ck1973  FLUENT  2  July 4, 2006 01:27 
Periodic boundary conditions in parallel fluent 6  Newuser  FLUENT  0  May 7, 2003 09:26 