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August 11, 2010, 12:36 
SIMPLE algorithm not converging.

#1 
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SGPrasath
Join Date: Jul 2010
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hi all,
I am new to CFD and i have started to code incompressible flow between two plates (given in anderson). The thing is, the code i have developed is not converging. the p' computed as given in anderson book, from the pressure poisson equation doesnot decrease. it keeps on increasing. The boundary conditions i have given are inlet: u=1, v=0, p'=0 exit: u(exit)=u(exit1), p'=0// column before exit top: u=0,v=0,p'=0 bottom: u=0,v=0,p'=0 Also, i dont know whether the way i am implementing staggering is correct or not. i have npx+2,npy+1 grid points for vcomponent npx+1,npy grid points for ucomponent npx,npy grid points for pressure. i am computing u momentum at 1 to npx1 and from 2 to npy1 and v momentum at 1 to npx and from 2 to npy1. what could be the reason for p' not comverging. thanks in advance, sgp. 

August 12, 2010, 03:21 

#2  
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Akinola
Join Date: Jul 2010
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Quote:
npx, npy+1 for vcomponents npx+1, npy for ucomponents npx, npy for the pressure. You should then compute umomentum from 1 to npx1 ( I assume your starting index is 0) and vmomentum from 1 to npy1 because the nodes 0 and npx/npy will coincide with points where the velocities are known. If you are using one of the other less common staggered grids, then maybe what you have now is correct. One thing that could cause convergence is your treatment of relaxation factor in the pressure correction equation. Are you incorporating it at all? 

August 12, 2010, 12:44 
under relaxation

#3 
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SGPrasath
Join Date: Jul 2010
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@falopsy
thanks for the reply. I am using underrelaxation factor for the pressure term as i read in Patankar's book that underrelaxation factor increases the stability of the code. Is it right? I also want to know if there is any sample code for SIMPLE algorithm by patankar available in internet. Thanks in advance, regards, sgp. 

August 12, 2010, 13:30 

#4  
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Akinola
Join Date: Jul 2010
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Quote:
"ftp://ftp.springer.de/pub/technik/peric/"  you can type the ftp directly in your browser. I think the code is based on collocated grid though but should still help somehow. 

August 12, 2010, 21:06 

#5 
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SGPrasath
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I think the velocity correction in pressure correction is just neglected.


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pressure poisson, simple 
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