Multiple BC error

KPraveen · June 21, 2015, 09:27

I am solving for a 3D jet in cross flow problem. I used the velocity inlet BC for the inlet and outflow BC for outlet.
But I get this warning:
Both outflow and pressure boundaries are present in the domain. This is an incompatibility and solution cannot proceed until this is fixed.
Also there is divergence detected in AMG solver for temperature, xyz momentum and pressure correction.

Please help.

pakk · June 22, 2015, 04:58

Quote:

Originally Posted by KPraveen

I am solving for a 3D jet in cross flow problem. I used the velocity inlet BC for the inlet and outflow BC for outlet.
But I get this warning:
Both outflow and pressure boundaries are present in the domain. This is an incompatibility and solution cannot proceed until this is fixed.
Also there is divergence detected in AMG solver for temperature, xyz momentum and pressure correction.

Please help.

Are you sure you don't have a pressure outlet/pressure inlet somewhere? Your error message suggests that you do.

KPraveen · June 22, 2015, 05:01

Yes, I used the pressure inlet condition on one inlet. I have two inlets and one outlet in this problem.

pakk · June 22, 2015, 05:20

So then the error is clear, not? You can not have a pressure inlet and "outflow" boundary at the same time.

So the solution is also clear, not? Change the pressure inlet to mass-flow inlet, or change the outflow to pressure outlet.

KPraveen · June 22, 2015, 05:38

I changed the outflow to pressure outlet BC . But still I am getting divergencce in AMG solver

pakk · June 22, 2015, 05:45

Then this is the point where you play around with numeric settings to get a convergent simulation. Use a different initialization, change underrelaxation factors, use different solver schemes, different discretizations...

If you have no feeling for it, then just play around, the only way to get experience is by trying things.

Unfortunately there is no "general" method that always work, otherwise everybody could do CFD.

KPraveen · June 22, 2015, 05:51

I will try pakk...........thanks .......

June 21, 2015, 09:27	Multiple BC error	#1
KPraveen New Member Praveen Join Date: Jun 2015 Posts: 8 Rep Power: 11	I am solving for a 3D jet in cross flow problem. I used the velocity inlet BC for the inlet and outflow BC for outlet. But I get this warning: Both outflow and pressure boundaries are present in the domain. This is an incompatibility and solution cannot proceed until this is fixed. Also there is divergence detected in AMG solver for temperature, xyz momentum and pressure correction. Please help.

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June 22, 2015, 05:01		#3
KPraveen New Member Praveen Join Date: Jun 2015 Posts: 8 Rep Power: 11	Yes, I used the pressure inlet condition on one inlet. I have two inlets and one outlet in this problem.

June 22, 2015, 05:20		#4
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 26	So then the error is clear, not? You can not have a pressure inlet and "outflow" boundary at the same time. So the solution is also clear, not? Change the pressure inlet to mass-flow inlet, or change the outflow to pressure outlet.

June 22, 2015, 05:38		#5
KPraveen New Member Praveen Join Date: Jun 2015 Posts: 8 Rep Power: 11	I changed the outflow to pressure outlet BC . But still I am getting divergencce in AMG solver

June 22, 2015, 05:45		#6
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 26	Then this is the point where you play around with numeric settings to get a convergent simulation. Use a different initialization, change underrelaxation factors, use different solver schemes, different discretizations... If you have no feeling for it, then just play around, the only way to get experience is by trying things. Unfortunately there is no "general" method that always work, otherwise everybody could do CFD.

June 22, 2015, 05:51		#7
KPraveen New Member Praveen Join Date: Jun 2015 Posts: 8 Rep Power: 11	I will try pakk...........thanks .......