[15326_jgs]

Hello

I am simulating a flow through a square section tube and I have to put dT / dx = 0 as a boundary condition at the output face (normal x-axis to the output face).

Any of the predefined Fluids B.C. satisfy this condition dT / dx = 0 ??

I am looking for it in the Ansys manual but I do not find anything.

Thanks in advance

[LuckyTran]

dT/dx = 0 means streamwise gradient is 0?


The outflow boundary condition makes the diffusive flux 0, which is equivalent to a neumann type BC in many scenarios. Most of the outlet type boundary conditions can also be used this way (by going to expert settings and disabling diffusion at the outlet). Fluent doesn't give you the option to hard clamp the streamwise derivative to be 0.

[15326_jgs]

Thank you for your answer.

How can I do that? Disable diffusion in the experts settings??

[LuckyTran]

Just use the outflow boundary condition?

[15326_jgs]

Originally Posted by LuckyTran

Just use the outflow boundary condition?

Ok. I am performing an unsteady state simulation with the boussinesq aproximarían for the density. I have seen in the ANSYS manual:

Note that outflow boundaries cannot be used in the following cases:
• if a problem includes pressure inlet boundaries; use pressure outlet
boundary conditions (see Section 6.8) instead
• if you are modeling compressible flow
• if you are modeling unsteady flows with varying density, even if the flow is incompressible

Regarding the last point, I am not sure if I can use this B.C. Is it correct if I use it?


I have another doubt. Outflow B.C. impose dP/dn = 0?? Zero Pressure gradient?? I need to implement this boundary condition

[LuckyTran]

None of the boundary conditions except the wall boundary condition impose the dP/dn = 0 condition. It physically makes no sense to use this condition except when there is a wall and hence it is not programmed. Mathematically it makes sense as a constraint, but physically no and it results in ill-posed problems. At a non-wall boundary, you have flow...

[Jerry190607]

Originally Posted by LuckyTran

None of the boundary conditions except the wall boundary condition impose the dP/dn = 0 condition. It physically makes no sense to use this condition except when there is a wall and hence it is not programmed. Mathematically it makes sense as a constraint, but physically no and it results in ill-posed problems. At a non-wall boundary, you have flow...

Can you please explain how to impose dp/dn=0 on a wall BC in CFX? Thank you very much!