Mass flow @outlet is greater than mass flow@inlet

bmayurm · July 10, 2015, 06:03

Hello dear all,
I am simulating a decanter (rotating frame). I have a boundary conditions are as @inlet mass flow rate is 4.16 kg/s and @outlet average static pressure is zero. After simulation in post-processing I found that @outlet mass flow rate is 4.45 kg/s which seems to be invalid.
Please tell me that at most general, what would be the conditions for such mismatch situation? Does meshing affects? How?
Please help me

ghorrocks · July 10, 2015, 06:19

Assuming this is a steady state simulation where the inlet must balance the outlet: It means you are not adequately converged. Run the simulation for more time steps.

For transient simulations it is a bit more complex.

bmayurm · July 10, 2015, 06:24

Thank you for replying Ghorrocks.
Yes, It is steady state incompressible simulation. I gave 100 iteration. Should I gave some more hundred so that it will have good convergence?

ghorrocks · July 10, 2015, 06:26

The residuals are what you should be watching to see if you are converged or not. And in this case as you have a problem with conservation I would use imbalances as well. You use as many iterations as are required to achieve the convergence you need.

bmayurm · July 10, 2015, 06:28

ok thank you

July 10, 2015, 06:03	Mass flow @outlet is greater than mass flow@inlet	#1
bmayurm New Member Mayur Bhandari Join Date: May 2015 Posts: 8 Rep Power: 10	Hello dear all, I am simulating a decanter (rotating frame). I have a boundary conditions are as @inlet mass flow rate is 4.16 kg/s and @outlet average static pressure is zero. After simulation in post-processing I found that @outlet mass flow rate is 4.45 kg/s which seems to be invalid. Please tell me that at most general, what would be the conditions for such mismatch situation? Does meshing affects? How? Please help me

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July 10, 2015, 06:19		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Assuming this is a steady state simulation where the inlet must balance the outlet: It means you are not adequately converged. Run the simulation for more time steps. For transient simulations it is a bit more complex.

July 10, 2015, 06:24		#3
bmayurm New Member Mayur Bhandari Join Date: May 2015 Posts: 8 Rep Power: 10	Thank you for replying Ghorrocks. Yes, It is steady state incompressible simulation. I gave 100 iteration. Should I gave some more hundred so that it will have good convergence?

July 10, 2015, 06:26		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	The residuals are what you should be watching to see if you are converged or not. And in this case as you have a problem with conservation I would use imbalances as well. You use as many iterations as are required to achieve the convergence you need.

July 10, 2015, 06:28		#5
bmayurm New Member Mayur Bhandari Join Date: May 2015 Posts: 8 Rep Power: 10	ok thank you