Continuity Residual Does Not Converge

victorz · April 29, 2013, 10:52

Hi all,

I'm solving a 3D compressible flow in a channel with perforated plates. I modeled the actual holes in the plates, rather than using the porous media approach.

I'm using a steady state solution, coupled scheme with quasi-transient approach.

After about 2500 iterations all my surface monitors have reached a steady state, the mass flow rate is perfectly balanced between the inlet and outlet, and all my residuals have converged, except for the continuity.

The continuity residual is reducing but at a very very slow pace, and at this stage it is ~6e-m.

Can I consider the solution converged? Should I continue the run (maybe beyond 10000 iterations)? In case the residual does not go below 6e-3, what should I do to obtain convergence?

Thanks!

oj.bulmer · April 29, 2013, 11:02

Have you checked the mass imbalance?

OJ

victorz · April 29, 2013, 11:05

Yes I did, the mass in/out is perfectly balanced, within 0.1% error.

oj.bulmer · April 29, 2013, 11:50

If solution is mesh independent, all the monitors are flat, mass imbalances are small enough to your liking, and there is a monotonicity in your residuals, then I don't see a reason you should be worried about. I have observed that even within 2-eqn models, Realizable models reduces continuity to much smaller values than RNG. This must just be a numerical artifact!

OJ

victorz · April 30, 2013, 01:49

Thanks a lot for the advice!

April 29, 2013, 10:52	Continuity Residual Does Not Converge	#1
victorz New Member Join Date: Sep 2011 Posts: 17 Rep Power: 14	Hi all, I'm solving a 3D compressible flow in a channel with perforated plates. I modeled the actual holes in the plates, rather than using the porous media approach. I'm using a steady state solution, coupled scheme with quasi-transient approach. After about 2500 iterations all my surface monitors have reached a steady state, the mass flow rate is perfectly balanced between the inlet and outlet, and all my residuals have converged, except for the continuity. The continuity residual is reducing but at a very very slow pace, and at this stage it is ~6e-m. Can I consider the solution converged? Should I continue the run (maybe beyond 10000 iterations)? In case the residual does not go below 6e-3, what should I do to obtain convergence? Thanks!

April 29, 2013, 11:50		#4
oj.bulmer Senior Member OJ Join Date: Apr 2012 Location: United Kindom Posts: 473 Rep Power: 20	If solution is mesh independent, all the monitors are flat, mass imbalances are small enough to your liking, and there is a monotonicity in your residuals, then I don't see a reason you should be worried about. I have observed that even within 2-eqn models, Realizable models reduces continuity to much smaller values than RNG. This must just be a numerical artifact! OJ RodriguezFatz, shyamal and toraman like this.

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April 29, 2013, 11:02		#2
oj.bulmer Senior Member OJ Join Date: Apr 2012 Location: United Kindom Posts: 473 Rep Power: 20	Have you checked the mass imbalance? OJ

April 29, 2013, 11:05		#3
victorz New Member Join Date: Sep 2011 Posts: 17 Rep Power: 14	Yes I did, the mass in/out is perfectly balanced, within 0.1% error.

April 30, 2013, 01:49		#5
victorz New Member Join Date: Sep 2011 Posts: 17 Rep Power: 14	Thanks a lot for the advice!