[Masroor]

Hello everyone,
I want to use the Fluent for modeling multiphase system in a cylindrical bubble column, I am referring a research paper that is about the similar modeling using OpenFOAM tool. I want to implement the same boundary conditions in ANSYS FLUENT that are set in OpenFoam setup. I am totally unknown of how to use OpenFOam and how to get the boundary conditons. I am writing down in brief about the boundary condition, I want some clarification.
Inlet BC:
1. Non-uniform gas volume fraction (Using UDF)
2. Fixed gas velocity
3. Liquid velocity is zero
When I used these conditions in ansys fluent, I found reversed flow in most of faces at outlet and my simulation stopped after very few time steps with FLUENT was exited itself. It was pressure outlet as outlet boundary condition with gas backflow of 1. I am not sure whether the problem is associated with UDF of boundary conditions.

I want to know about Outlet Boundary conditions of openfoam so that I can set in ansys fluent. these are given below

1. Inletoutlet BC for gas volume fraction.
2. pressureInletOutletVelocity for gas velocity

Kindly provide your valuable suggestions how to set same boundary conditions in ANSYS FLUENT.
Thanking you in advance and looking forward to receive a quick and valuable suggestions from your end.

[PanPeter]

Hi Masroor,

The two BCs inletOutlet and pressureInletoutletVelocity are acting as outlet boundaries (zero gradient), if the velocity is directed outward. If it is directed in inward, a specified fixed value (inletOutlet) or a pressure-dependent dynamically specified value (pressureInletOutletVelocity) is assigned to the respective field.

This is a neat way to fix the problem you're facing in Fluent: An outlet boundary defines a zero gradient, independent of the flow direction. But if you have back flow at that outlet, it practically acts as an inlet and the quantities have to be calculated from the gradient there, which often leads to high fluctuations in pressure and velocity. Possibly that's why your Fluent sim crashes.

I don't think Fluent has an equivalent BC to inletOutlet, so I would write a small UDF for these. You can find the description of the two OpenFoam BCs in the documentation:
https://cfd.direct/openfoam/user-gui...24-1730005.2.2
cheers,
Fynn