Source terms in equations

klilla · November 25, 2009, 08:23

Dear All,

I try to add source terms in all the equations in coodles. When I add one to the density - so to the continuity equation - I found a rather strange behaviour. I printed out the magnitude of my source term from the function it calculates and from the solver itself (like rhoEqn.source()). Good news, they coincide. On the other hand:

diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0

It seems that the sources computed and assigned, but during the iterations they are not considered.

Can anyone help me on this issue?

Thanks,

Lilla

niklas · November 25, 2009, 08:35

If you're adding a source term to the continuity equations dont forget the addition to the PISO loop.

klilla · November 25, 2009, 08:39

I did modify it as well. Unfortunatelly.

klilla · November 26, 2009, 06:40

I've performed an other test as well. Now with the original OF solver, so without source terms. It is a cavity flow. In fact the simulation is running, and the results seems meaningful. But I still have that funny line:

diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0

Have anyone idea why is it like that?

Thanks,

Lilla

niklas · November 26, 2009, 06:56

because your matrix is purely diagonal.

fvm::ddt(rho) + fvc::div(phi) = S

produces a matrix-vector system like A*rho = H

and if A dont have any offdiagonal elements you can solve for rho exactly in 1 iteration.

November 25, 2009, 08:23	Source terms in equations	#1
klilla Member Kapa Lilla Join Date: Mar 2009 Location: Bruxelles, Belgium Posts: 57 Rep Power: 17	Dear All, I try to add source terms in all the equations in coodles. When I add one to the density - so to the continuity equation - I found a rather strange behaviour. I printed out the magnitude of my source term from the function it calculates and from the solver itself (like rhoEqn.source()). Good news, they coincide. On the other hand: diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 It seems that the sources computed and assigned, but during the iterations they are not considered. Can anyone help me on this issue? Thanks, Lilla

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November 25, 2009, 08:35		#2
niklas Super Moderator Niklas Nordin Join Date: Mar 2009 Location: Stockholm, Sweden Posts: 693 Rep Power: 29	If you're adding a source term to the continuity equations dont forget the addition to the PISO loop.

November 25, 2009, 08:39		#3
klilla Member Kapa Lilla Join Date: Mar 2009 Location: Bruxelles, Belgium Posts: 57 Rep Power: 17	I did modify it as well. Unfortunatelly.

November 26, 2009, 06:40		#4
klilla Member Kapa Lilla Join Date: Mar 2009 Location: Bruxelles, Belgium Posts: 57 Rep Power: 17	I've performed an other test as well. Now with the original OF solver, so without source terms. It is a cavity flow. In fact the simulation is running, and the results seems meaningful. But I still have that funny line: diagonal: Solving for rho, Initial residual = 0, Final residual = 0, No Iterations 0 Have anyone idea why is it like that? Thanks, Lilla

November 26, 2009, 06:56		#5
niklas Super Moderator Niklas Nordin Join Date: Mar 2009 Location: Stockholm, Sweden Posts: 693 Rep Power: 29	because your matrix is purely diagonal. fvm::ddt(rho) + fvc::div(phi) = S produces a matrix-vector system like A*rho = H and if A dont have any offdiagonal elements you can solve for rho exactly in 1 iteration.