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-   -   Pressure outflow w/ species; mass frac. required? (http://www.cfd-online.com/Forums/fluent/42421-pressure-outflow-w-species-mass-frac-required.html)

Myth September 29, 2006 14:15

Pressure outflow w/ species; mass frac. required?
 
Hi all,

I'm trying to run a standard simulation of gas uptake along a tube, and I've found that when using standard outflow, I only need to provide flow weighting, but the solver doesn't always converge well.

When using a pressure outflow, which gives me the needed flow convergence, I have to also specify a mass fraction at the outlet-- is there any way around this, to deactivate that boundary condition requirement, so that I can let the solver determine the outlet mass fraction? The very nature of my simulation is to determine the outlet mass fraction; it is not a value I can even guess offhand.

Thanks in advance.

vitmalin September 29, 2006 19:29

Re: Pressure outflow w/ species; mass frac. requir
 
Try to use targeted mass flow option with pressure outlet bc

Swarup September 29, 2006 23:08

Re: Pressure outflow w/ species; mass frac. requir
 
Hi,

The outlet mass fraction is not what you consider it to be. If there is any reverse flow (flow enters thru outlet) then that occurs with the mass fraction you set. This setting should be realistic. If component X does not enter from inlet 0 is the logical setting for that component.

Thus, solver is doing the job and you need not "deactivate" any setting.

Swarup.


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