[waseeqsiddiqui]

Any way to specify all three quantities together in inlet for a pipe internal flow?
Far Field has all these conditions but they changes if i specify mass flow rate outlet!
What works well in the outlet with far field?

[LuckyTran]

Yes but that would imply that the inlet is supersonic.

[waseeqsiddiqui]

what works well with far Field?
like velocity inlet and outflow

[LuckyTran]

The farfield BC type should not be used at inlets or outlets. It is meant to be used as a natural boundary condition, i.e. at infinity. You have a pipe... You don't have a farfield. You have and and outlet. If you don't know what BC's to use, then you are lost and need to figure out what BC's you have.

[waseeqsiddiqui]

Yes. But surprisingly people use pressure outlet and mass flow rate with far field.
Thanks

[LuckyTran]

You have a pressure outlet with targeted mass flow rate option.


What the heck is a farfield mass flow rate? This exists in Fluent?

[waseeqsiddiqui]

If we give mass flow rate to the outlet and far field to the inlet that way this exists.

[LuckyTran]

There's clearly a language barrier here and it makes it difficult to diagnose your issue.

There is a farfield BC which should never be used at inlets or outlets. If you use it at inlets and outlets despite this, it may be that that it does not blow up and you will get some solution. I'm not going to discuss anything about this solution because in my opinion it makes no sense and is not worth even looking at.

You want to specify velocity, pressure, and temperature at an inlet. This is possible (mathematically and physically) only if the flow at the inlet is supersonic. You simply need to use a mass flow inlet and specify the supersonic static pressure. However, your downstream BC must support the flow being supersonic. If your pipe flow is supersonic that's all you have to do. If its subsonic, then you are tryning to do something non-physical. You can try to obtain a solution that has a temperature and pressure that you want by iterating the other BC's, but that's not the same as imposing a hard constraint on the inlet pressure and temperature.

The farfield BC does not strictly impose the static pressure and static temperature at the boundary, it sets the local static pressure and static temperature such that it it relaxes to the freestream values following characteristics. In other words, the farField BC doesn't even do what you want it to do, why are you even talking about it?


There is no mass-flow rate outlet BC per se. There is a mass flow rate inlet and a pressure outlet (with targeted mass flow rate). What Fluent does is it adjusts the outlet pressure until you get the desired mass flow rate. It's actually still a pressure outlet. You can however, put a mass flow rate inlet and reverse the direction to get a mass flow rate outlet, this is again non-physical.

[waseeqsiddiqui]

Understood. Well Explained!
But I am certain I have seen publications with far field utilized as a BC inlet condition. I'll share a relevant paper soon sometime.