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

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).

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

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

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.

Don't specify negative mass, just specify the direction vector to be negative to the boundary!