September 8, 2023 at 5:06 pmbv169Subscriber
I am running an open channel multiphase model. When any backflow enters the outlet, the model crashes as there is divergence in the residuals. I finally figured out it is due to the wrong phase entering as backflow. Is there a way to control this? or turn off backflow?
September 11, 2023 at 1:40 pmSRPAnsys Employee
In the boundary condition, you can set the volume fraction for the backflow.
You can check fluent user manual for more detail: 25.2. Steps for Using a Multiphase Model (ansys.com)
September 11, 2023 at 1:46 pmRobAnsys Employee
If you look in the phase options in the outlet you'll find what you're looking for. However, if you're using Open Channel VOF you should find options to set the free surface level.
September 11, 2023 at 4:04 pmbv169Subscriber
Yes, I am setting the free surface level at the inlet and outlet. Despite that it seems my phase from above that level is entering as backflow below that level. When open channel is turned on, I don't see the option to set the volume fraction for backflow...
September 11, 2023 at 4:17 pmRobAnsys Employee
It shouldn't unless you have another boundary that's not been set? Pictures will help us as we're guessing at present.
September 11, 2023 at 6:05 pm
September 12, 2023 at 12:11 pmRobAnsys Employee
If you're using open channel why is the domain full of water? The second image looks to be a diverged result so not overly diagnostic.
September 12, 2023 at 1:37 pmbv169Subscriber
The domain isn't completely full, but it is mostly full. The air phase is only about 5 meters at the top of the domain. Thanks for the info regarding the contour, I can try to evaluate where the divergence in vof is coming from before it gives the error to get a better diagnosis of the issue.
September 12, 2023 at 2:06 pmRobAnsys Employee
What did you set on the top boundary as the backflow phase?
September 12, 2023 at 2:44 pmbv169Subscriber
The top was set to a wall in this run. I just looked into changing the top boundary to an outlet/outflow and don't see the volume fraction option in any of the boundary types.
September 12, 2023 at 2:56 pmRobAnsys Employee
Pressure outlet - there should be a phase option. Do NOT use outflow, it's an old boundary and isn't recommended for use in most cases.
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