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.

Deborah

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.

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

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.

Neale.

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!