[mnws]

Dear all,

Is it possible to write a field function that reads in three variables (Pressure, velocity and temperature) to define a boundary condition for an inlet?

The BCs such as stagnation inlet, velocity inlet, wall, free stream and pressure outlet are NOT suitable, please do not suggest using those, as I need to define three variables for the inlet.

Just want to know if this is possible or not.

Best,

Mnws

[LuckyTran]

Yes, just use a velocity inlet. The velocity inlet is the only BC that allows you specify everything. It is prototyped based on the fixed values constraint. But since that doesn't work for you, for whatever mysterious reason, then no.

[mnws]

Dear LuckyTran,

Thanks for your suggestion. The reason why it doesn't work for my case is because I want to simulate the exhaust flow entering a turbine passage. So the exhaust flow includes pressure, velocity and temperature. Only two variables would be insufficient to define the inlet conditions.

Do you know of any solutions? Is it possible to attach a third physical property (i.e. pressure) to the velocity inlet? I only know of the use of field functions for the prescribed physical properties, don't know if I can add any new variables.

Thanks

[LuckyTran]

I thought maybe you were working on something actually complex like implementing non-reflecting characteristic boundary conditions where you would actually need to specify all three. If you're just trying to specify stuff at an inlet.... Two variable is all you ever need. More just overdefines the problem and will give you trouble elsewhere, there is no free lunch.

The only time you can physically specify static pressure, temperature, and velocity at the inlet is if it is supersonic. I highly doubt your turbine is supersonic. If your inlet is subsonic and you still want to specify these things, then you do not want to be solving Navier-Stokes equations. You need to re-wire your thinking.

You don't need to specify all three at the inlet. You just want to. Stop wanting. Or find another way to get what you want without violating physical laws. Or stop using a physics-based solver.

Btw I totally empathize for your wants. I've wanted to specify pressure, temperature, and velocity at inlets many many many many times.


What you can do is use a velocity inlet and something like a pressure outlet with the targeted mass flow rate option. Since the inlet velocity and temperature are specified, and the massflow is also applied as a constraint, the density and pressure at the inlet will eventually drift towards the static pressure that you want.