[shivasluzz]

A rotating cylindrical tank initially filled with air, in which oil is entering from one side (inlet). When the oil fills the rotating tanks, the air enters or leaves from another side (say a circular opening), depends on the pressure inside due to the rotation and oil inflow. When the oil fills the tank, then the further oil addition should flow out from the same same circular opening.

So the condition for Circular opening is:
1. air should come in or go out.
2. oil should only go out.

How to set up this boundary condition for the circular opening? Is the 'opening boundary' with volume fraction for both oil and air is 0.5, suitable? what is the value of 0.5 signifies here ? (i understood the value of 0 and 1 for initial condition)

Also, in Opening boundary, the inflow can happen only due to re circulation or will it assume there is fluid addition at that boundary just like inlet.


Please help.
Thanks

[ghorrocks]

VF=0.5 means half the control volume is air, half is oil.

Before you implement this unusual boundary condition - can you explain how it comes about physically? Is there some device on the boundary which makes it behave as you describe?

I do not understand your other questions. An opening either flow entering the domain (in which case it is assigned the volume fraction you define), or leaving the domain and no volume fraction need be defined as the fluid leaves the domain.

[Opaque]

From the documentation

2.5.1.9. Degassing Condition (Multiphase only)

Degassing boundary conditions are used to model a free surface from which dispersed bubbles are permitted to escape, but the liquid phase is not. They are useful for modeling flow in bubble columns.

When Degassing Boundary Condition is selected as the Flow Specification of an outlet, the continuous phase and any dispersed solid phases that may be present see this boundary as a free-slip wall and do not leave the domain. Dispersed fluid phases and Lagrange particles see this boundary as an outlet. However, the outlet pressure is not specified. Instead, a pressure distribution is computed on this fixed-position boundary, and can be interpreted as representing the weight of the surface height variations in the real flow.

Because the Degassing Boundary Condition does not specify a pressure value, a fixed pressure reference point will be set automatically for a domain with an incompressible flow with degassing boundaries, but no pressure boundaries.

You want an "opening degassing condition" instead of the outlet version. I would check with ANSYS CFX support to see if there is such BC already implemented in beta mode, or guidance on how to go from the outlet to the opening style.

Hope the above helps,

[shivasluzz]

Thanks ghorrocks.. I understood...
Opaque, Degassing boundary is applicable for dispersed fluid not for continuous fluid.
Sorry for the very late reply :-P