
[Sponsors] 
Pressure equation in presence of obstacles with a Colocated grid 

LinkBack  Thread Tools  Display Modes 
February 18, 2013, 00:35 
Pressure equation in presence of obstacles with a Colocated grid

#1 
New Member
Aryan
Join Date: Jan 2013
Posts: 8
Rep Power: 4 
Hi
I have written a 2D code for the SIMPLE method on the colocated grid. I want to study the fluid flow around an obstacle. For this purpose, I alter the source terms appeared in the momentum equation such that the velocity in the obstacle region is zero. But I have problem with the pressure equation. Since the velocities in the solid zone are zero, all of the coefficient s of aW, aE, aS, aN, Su, Sp and aP are zero for the pressure equation (actually very small values because of the numerical and round off errors). This causes a wrong solution for the pressure and consequently the momentum equations. I was wondering if someone could help me to solve this problem. Regards 

February 18, 2013, 00:51 

#2 
New Member
Lipo Wang
Join Date: Dec 2012
Posts: 14
Rep Power: 4 
Hi,
You need to deal with the boundary cells specially to ensure the correct boundary conditions of pressure (to solve the Poission eq.). It may not be feasible to treat all of the cells in a general way. 

February 18, 2013, 01:01 

#3 
New Member
Aryan
Join Date: Jan 2013
Posts: 8
Rep Power: 4 
Hi nickna
But I think this is practical: "Computational Flow Modeling for Chemical Reactor Engineering" By Vivek V. Ranade, Page 172. 

February 18, 2013, 07:43 

#4  
Senior Member
andy
Join Date: May 2009
Posts: 129
Rep Power: 8 
Quote:
A colocated arrangement requires the introduction of "pressure smoothing" in order to prevent pressurevelocity decoupling. It looks as if you are doing this in an implicit manner by fiddling/averaging coefficients rather than with explicit pressure gradient terms. A first step could be to work out what your smoothing fluxes actually are and whether you want to apply them at the boundaries. For example, swirling flow in collocated schemes tends to jump badly at boundaries when the large pressure smoothing term at the boundary is not included. For incompressible flows a pressure equation can be derived from the momentum equations and then constrained to be divergence free. This can be used to determine good treatments for pressure on the boundary given your particular numerical scheme. There is plenty in the literature on this topic. 

February 19, 2013, 00:23 

#5 
New Member
Aryan
Join Date: Jan 2013
Posts: 8
Rep Power: 4 
Hi andy
Thanks for your guidance but I still think that the problem remains, as it occures in my code apparently. When the velocity in the block zone is zero the fluxes are zero and consequently the pressure equation coefficients are also zero. Correct? 

February 19, 2013, 00:25 

#6  
New Member
Aryan
Join Date: Jan 2013
Posts: 8
Rep Power: 4 
Quote:
Thanks for your guidance but I still think that the problem remains, as it occures in my code apparently. When the velocity in the block zone is zero the fluxes are zero and consequently the pressure equation coefficients are also zero. Correct? 

February 19, 2013, 02:26 

#7  
Senior Member
Arjun
Join Date: Mar 2009
Location: Nurenberg, Germany
Posts: 372
Rep Power: 10 
Quote:
If you decided to treat the solid part as fluid then it has viscosity and thus coefficients are not 0. If you decided to treat solid part as solid then you do not need to solve pressure correction equation in this part and thus this does not go into matrix so coefficients have no meaning. 

Tags 
colocated obstacle 
Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
SIMPLER Pressure boundray condition for collocated grid  fard  Main CFD Forum  0  September 26, 2011 10:16 
Poisson equation for pressure homogeneous boundary condition  RenardP  Main CFD Forum  1  July 13, 2009 10:01 
Reynolds transport, turbulence model, etc  Beginner  Main CFD Forum  1  January 7, 2009 06:36 
Dirichlet BC for Pressure Poisson Equation  Chandra  Main CFD Forum  11  October 29, 2008 04:32 
BC for Pressure Correction on Colocated Grid  Matt Umbel  Main CFD Forum  1  October 3, 2000 19:44 