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Deborah March 27, 2003 09:23

Mass flow rate specification
Hi all!

My geometry consists in a duct with inlet and outlet boudaries acting as periodic pair. In order to define the mass flow rate, I have create a sub-domain (which is the entire domain).For the source term I have the choice between "momentum", "mass source",... but not "mass flow rate". How can I do?

Thanks in advance.


Martin Bowers March 28, 2003 11:48

Re: Mass flow rate specification
Long way: Figure out what the correction distribution of momentum sources is to create the fully developed flow field I'm assuming you're looking for. For a straight pipe it's constant, anything else: probably not. You will have to find some way to iterate on the average value until you get the right mass flow rate.

Short way: Buy Fluent and just specify mass flow rate.

Future way: Maybe CFX will implement a periodic mass flow rate BC.

Glenn Horrocks March 30, 2003 18:28

Re: Mass flow rate specification
Hi Martin,

I think CFX4 has this type of boundary condition you describe. There is no need to go across to the dark side. Hopefully CFX5 will implement this type of BC in a future release.

Regards, Glenn Horrocks

Neale April 1, 2003 02:00

Re: Mass flow rate specification
This is certainly a non-trivial boundary condition to robustly implement in a coupled-implicit solver.

You could use a static pressure inlet and mass outlet, set the timestep small enough, and hope to hell things "hold on". It might work OK for an incompressible flow.


Martin Bowers April 1, 2003 13:59

Re: Mass flow rate specification
Well I can appreciate that the BC might not be as easy to implement into a coupled implicit solver, but I haven't seen any justification as to why exactly.

If the implementation is just a matter of balancing a global source term against the desired mass flow rate, why does the user have to do that tedious iterative work when the code doesn't? - It is an iterative solver after all!

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