[limowaagung11]

I Have A Model And I Use fluent, the problem is the outlet direction vector is not aim the right way. The direction vector on the duct outlet is moving back to the duct instead of pointing in the right direction (out from duct).

Does anyone Know What Happening? And Also I have a large model about 2 km in length and I am using a mass flow outlet. The fluent always says Turbulent viscosity limited (I am using standard epsilon) and then floating point error, but if i change the outlet to pressure outlet it runs just fine (But my goal is to control the mass value and not just pressure) . Does anyone know what should i do?

[LuckyTran]

Fluent doesn't have a "mass flow outlet" so what BC are you actually using?

You may use a pressure outlet and enable the targeted mass flow rate option if you want to specify an outlet flowrate. It is a pressure outlet condition but adjusts the outlet pressure until the set mass flowrate is achieved.


Regarding the vectors. What vector are we even looking at? Velocity or Area? Boundary area vectors point inwards by convention.

[bgp723]

Hi Lucky, just wanted to jump in to say that FLUENT actually does have mass flow outlet BC. See picture.
Not sure when this BC type was added... I'm using ANSYS FLUENT 2022R1/2.

As for limo's issue, I'm not sure why your outlet vector is pointing inward or why you are getting different issues with pressure outlet vs mass flow outlet... I never personally had issues using mass flow outlet BC. Only thing I can think of is maybe you don't have mass conserved assuming you are using mass flow inlet BC as well (i.e. your total in is not equal to total out), but that still doesn't resolve your outlet vector pointing weirdly. It's difficult to tell from the picture too. Do you have some weird mesh interface around the outlet?

[LuckyTran]

I stand corrected. Quickly reading through the notes reveals that it is essentially a reskinned mass flow inlet (hah!), something we don't recommend to use in general. If there is any reversed flow this BC is cooked. I still would recommend to use the pressure outlet with targeted mass flow rate option.


Anyway I guess we can appreciate why Fluent has always had this capability but never explicitly labeled it a mass flow outlet. Because ppl would be too happy to use it.