Learning Forum

[xing]

Does FLUENT allow us to apply periodic boundary conditions (PBC) for two phase flow.  For example, we have an open channel flow with both air and water.  Can we apply PBC at inlet and outlet to obtain the fully developed velocity profile?  Note, we need to specify different pressure gradients for air and water.  We already tried "open-channel flow model" in FLUENT but it didn't work for our case. Because FLUENT forces the free surface to be normal to the gravity force whereas we need to model the slope of the channel, i.e., the free surface has an angle with the gravity force.

[DrAmine]

It should be feasible to run open channel flow model with slope.

Regarding your question you can use periodic boundary and provide a pressure drop for the bulk weighted by the volume fraction for VOF or using Eulerian model with source terms in every momentum equation set.

[xing]

Amine, in FLUENT manual, it clearly states that FLUENT open channel flow model (OCFM) always assumes that the free surface is normal to the gravity.  In our experiments or in real river flows, that is not true even the slope is not that large.  How can I resolve this?  We have tried to tilt the domain or change the gravity vector but again FLUENT forces the free surface to be normal to the gravity force, which causes un-physical water depth at outlet.

Could you please provide a tutorial on how to set up the periodic boundary condition for two phases?

[DrAmine]

There is no tutorial on how to add this kind of source terms. The height definition is along the normal that is true but one can run cases with slope etc. I guess that is something related to initialization.