SIMPLEC Method

meshkati · November 7, 2009, 08:13

Hey everyone,
I try to develop a CFD code by solving 3D Navier-Stocks equations in curvilinear coordinates. But I have a problem with coupling of pressure and velocity (pressure correction equation - p’) that I use SIMPLEC method for it.
In initial iterates (that no pressure gradients exists in domain) the momentum equations have no source term and then: ap=sigma(a_neighbors).
Therefore the parameter of [ap - sigma(a_neighbors)] that appears in the denominator of SIMPLEC method equals to zero and then the divides by zero error was occurred.
What can I do?
Thanks for advance.
Hadi
(Some of my code specifications are: Finite volume method, non -staggered grid, incompressible fluid, steady calculation, no free surface calculation, Rhie and Chow interpolation method, laminar or k-e turbulence model, SIMPLEC pressure correction method and the test case is straight channel with uniform velocity boundary condition in its inlet and if any another comments was needed just tell me)

ztdep · November 7, 2009, 20:22

Ap is the value after under-relaxation. for example , Ap/0.6 Ap/0.6-Sigam (A neighbour) >0

hadian · November 8, 2009, 06:03

also, it is recommended to add Delta_F (Fe-Fw+Fn-Fs+Ft-Fb) to Ap.

meshkati · November 14, 2009, 06:48

Quote:

Originally Posted by ztdep

Ap is the value after under-relaxation. for example , Ap/0.6 Ap/0.6-Sigam (A neighbour) >0

That's right, but in SIMPLEC method we can assume all under relaxation factors equals to one (for faster convergence). Then ap equals to ap/urf.

ztdep · November 15, 2009, 02:47

Quote:

Originally Posted by meshkati

That's right, but in SIMPLEC method we can assume all under relaxation factors equals to one (for faster convergence). Then ap equals to ap/urf.

" in SIMPLEC method we can assume all under relaxation factors equals to one "
i do not agree with you. if a 1 is used. the simplec will destinated to divergence

universez · November 18, 2009, 21:58

Quote:

Originally Posted by hadian

also, it is recommended to add Delta_F (Fe-Fw+Fn-Fs+Ft-Fb) to Ap.

what is meaning of Delta_F (Fe-Fw+Fn-Fs+Ft-Fb) ?

hadian · November 19, 2009, 00:48

Delta_F=Fe-Fw+Fn-Fs+Ft-Fb and these are convective fluxes passes control volume faces. actually this is the continuity equation and should be zero but it is not zero during the iterations. have a look on the book by Versteeg and Malalaskera.
also, note that in unsteady form of equation you have a A0 which added to Ap. so that Ap-SUM(Anb) will not be zero. moreover a relaxation factor is recommended.

November 7, 2009, 08:13	SIMPLEC Method	#1
meshkati New Member S.M. Hadi Meshkati Join Date: Nov 2009 Posts: 7 Rep Power: 16	Hey everyone, I try to develop a CFD code by solving 3D Navier-Stocks equations in curvilinear coordinates. But I have a problem with coupling of pressure and velocity (pressure correction equation - p’) that I use SIMPLEC method for it. In initial iterates (that no pressure gradients exists in domain) the momentum equations have no source term and then: ap=sigma(a_neighbors). Therefore the parameter of [ap - sigma(a_neighbors)] that appears in the denominator of SIMPLEC method equals to zero and then the divides by zero error was occurred. What can I do? Thanks for advance. Hadi (Some of my code specifications are: Finite volume method, non -staggered grid, incompressible fluid, steady calculation, no free surface calculation, Rhie and Chow interpolation method, laminar or k-e turbulence model, SIMPLEC pressure correction method and the test case is straight channel with uniform velocity boundary condition in its inlet and if any another comments was needed just tell me)

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November 7, 2009, 20:22		#2
ztdep Senior Member p ding Join Date: Mar 2009 Posts: 427 Rep Power: 19	Ap is the value after under-relaxation. for example , Ap/0.6 Ap/0.6-Sigam (A neighbour) >0

November 8, 2009, 06:03		#3
hadian Member Mohammad Reza Hadian Join Date: Mar 2009 Location: Yazd, Iran Posts: 52 Rep Power: 17	also, it is recommended to add Delta_F (Fe-Fw+Fn-Fs+Ft-Fb) to Ap.

November 19, 2009, 00:48		#7
hadian Member Mohammad Reza Hadian Join Date: Mar 2009 Location: Yazd, Iran Posts: 52 Rep Power: 17	Delta_F=Fe-Fw+Fn-Fs+Ft-Fb and these are convective fluxes passes control volume faces. actually this is the continuity equation and should be zero but it is not zero during the iterations. have a look on the book by Versteeg and Malalaskera. also, note that in unsteady form of equation you have a A0 which added to Ap. so that Ap-SUM(Anb) will not be zero. moreover a relaxation factor is recommended.