Mass Flow Rate is Not Conserved

yanqoue · November 18, 2019, 02:19

I have a problem with Pressure Inlet & Pressure Outlet condition.
At the inlet, cross section area is bigger and I have some mass flow rate. Further into downstream cross section gets smaller and mass flow rate also gets smaller, the difference is not small as well. Shouldn't it be conserved?

ghorrocks · November 18, 2019, 04:21

Assuming a converged, steady state simulation with an inlet and an outlet, then yes the inlet and outlet flows will be the same. If yours does not then your simulation is not converged. Run it for more iterations.

Opaque · November 18, 2019, 09:57

In addition to Glenn's comments, how are you computing the mass flow? i.e. are you looking at solver computed values for mass flow? or are you computing the mass flow yourself?

November 18, 2019, 02:19	Mass Flow Rate is Not Conserved	#1
yanqoue New Member nicola Join Date: Sep 2016 Posts: 24 Rep Power: 10	I have a problem with Pressure Inlet & Pressure Outlet condition. At the inlet, cross section area is bigger and I have some mass flow rate. Further into downstream cross section gets smaller and mass flow rate also gets smaller, the difference is not small as well. Shouldn't it be conserved?

November 18, 2019, 04:21		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,819 Rep Power: 144	Assuming a converged, steady state simulation with an inlet and an outlet, then yes the inlet and outlet flows will be the same. If yours does not then your simulation is not converged. Run it for more iterations. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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November 18, 2019, 09:57		#3
Opaque Senior Member Join Date: Jun 2009 Posts: 1,852 Rep Power: 33	In addition to Glenn's comments, how are you computing the mass flow? i.e. are you looking at solver computed values for mass flow? or are you computing the mass flow yourself?