Unknown(atmospheric) boundary condition for external flow
 

Hi all

I'm simulating a flow around a vehicle in atmospheric condition, so I made a rectangular flow space surrounding the vehicle.
Inlet is velocity inlet, and outlet is pressure outlet.

Things are upper boundary and side one. Air can come inside the space or go out from the space through upper&side plane.

At first, I used a non-slip wall, but it's a tunnel, not atmosphere.
Of course, it can be approximated as an atmosphere if the flow space is large enough, but it is not sure yet.


I think there are three candidates: pressure outlet, outflow, free-slip wall.

Pressure outlet is not proper. Because I should fix the pressure at that plane, but the pressure is unknown.
Outflow is also not proper, because there may be a streamwise gradient.
I have no idea about free-slip wall.


What can I do??
Am I even understanding correctly?

Any comment will be highly appreciated!!

Thanks in advance.

Hello swtbkim,
I suggest using a symmetry boundary condition: if you increase your domain so that boundaries are far enough from the vehicle, you can neglect fluxes through these boundaries.

Regards

Thank you for your reply, Flavio
But I don't understand what you say. Symmetry at sky??

Can you explain more?