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-   -   outlet massflow boundary condition ?? (http://www.cfd-online.com/Forums/fluent/28827-outlet-massflow-boundary-condition.html)

Charles Renard August 17, 2001 05:44

outlet massflow boundary condition ??
 
hi !

i am wondering how to model a fresh air entry on a vehicle.(i am currently working on external aerodynamics) i already modeled the corresponding hot gases oulet with a mass flow inlet boundary condition.

my issue is that i only know the mass flow rate (the same as for hot gases outlet), and it seems that fluent 5 has no "outlet massflow" boundary condition.

Help needed !

thanks Charles

Chetan Kadakia August 19, 2001 02:05

Re: outlet massflow boundary condition ??
 
Use 'outflow' for your exit BC. This is a simple BC that I beleive says that your inlet massflow(s) is equal to the outlet here (when flow weighting is 1).


Mark Richardson August 19, 2001 11:44

Re: outlet massflow boundary condition ??
 
Charles, I have not done this to test my theory but is a mass outflow just a negative mass inflow?

When I check the fluxes (Report->Fluxes, compute) I get opposite values of equal magnitude at my pressure inlet and pressre outlet for mass flow rate.

Luck, Mark

Charles Renard August 20, 2001 03:23

Re: outlet massflow boundary condition ??
 
Hi !

Unfortunately, giving a negative inlet massflow doen not work, fluent doens not accept it.

as a solution to my issue, i entered a negative inlet velocity corresponding to the massflow (and area of course...). this last solution was accepted by the software and seems to work....

but i still believe it would be great to have a real outlet massflow bc in fluent ;-)

thanks Charles


Jonas Larsson August 23, 2001 16:42

Re: outlet massflow boundary condition ??
 
You can easily write a scheme file which updates the static pressure of a pressure-outlet to match a certain specified mass-flow. I even think that this is an example that Fluent will give to you - if you ask support I'm sure they'll send it to you. If I remember correctly it has also been posted here some time ago... found it btw, it is here.

Lanre August 24, 2001 15:47

Re: outlet massflow boundary condition ??
 
Don't specify negative mass, just specify the direction vector to be negative to the boundary!


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