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

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).

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

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

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.

Re: outlet massflow boundary condition ??
 

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