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What are Free Surface Level and Bottom Level

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Old   October 20, 2021, 19:00
Default What are Free Surface Level and Bottom Level
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berat
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Hello guys,

so i have a hard time understanding what the Free Surface Level and Bottom Level are and how they are actually related to the boundary conditions in multiphase flow.

Maybe some background information first. I am using the VOF model to simulate an "open channel" with water and air. I have a pressure outlet and a mass flow inlet. When setting the boundary condition i can chose/check mark the open channel option which allows me to specify the Free Surface Level and the Bottom Level. According to the Fluent User Guide, these are the heights of the Surface and the bottom of the fluid, starting from the reference coordinate system.

Now to my question. If u take look at the little sketch I provided, the inlet is strictly separated from the free surface. Fluent whats me to set the free surface level and the bottom level as part of the inlet boundary condition. Now I am somewhat confused on how I should handle these levels because I do not have the surface at the boundary. If I had a standard open channel flow, where the free surface is in direct contact with the boundary, that would be straight forward I believe. But in my case, I am even questioning whether my problem can be even classified as an open channel flow.

thanks in advance
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Old   December 6, 2021, 20:40
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xu weicheng
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I think the inlet boundary condition is not necessary to set as open flow bc.
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