Is there a way to specify a mass-flow boundary condition (e.g. mass flow rate at outlet)? The inlet mass-flow rate is out of the question due to many considerations (compressibility effects with Mach number around 0.8 being one of them). Imagine a vacuum cleaner for which mass flow rate is known and you are required to estimate its efficiency in terms of what area it covers and how much of dust it sucks in.

yes it is

/define/boundary-conditions/target-mass-flow-rate-settings>

there are two ways to define it . please refer to fluent users guide for description

regards

Thank you, SAM. It seems fairly easy indeed. Although a further step is required - an unsteady targeted mass flow rate at outlet. I have tried to hook up a udf procedure normally used for mass-flow_inlet and failed .

i have no idea for udf and unsteady flow fenomena

1) A scalar was defined.

Then: 2) define -> boundary conds -> pressure ... [standard points] and:

Use profile for scalar value [no]? yes

Profile name [""] "udf"

data name [""] suck_in_rate

!!! And then it prompts: specify targeted mass-flow rate !!! What am I supposed to do?

If you know the mass flow at the outlet, just call it a massflow-inlet, but specify the direction to exit at the outlet.

And in that case, you can use a 0 pressure inlet too, since you are sucking in from atmospheric conditions. I use that all the time: pressure inlet at inlet, and mass flow inlet for the outlet.

Good suggestion. Thanks. Tried it in the first place though. Convergence was pretty awful. And it never worked with the coupled solver.