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Tony September 26, 2004 17:04

Boundary condition of free surface model
Dear all,

I use Fluent to model the water ejecting from a small pipe. I tried to use VOF model and define the free surface area as pressure_inlet, but it did not converge. My model has one velocity_inlet, one pressure_inlet and one pressure_outlet. Can anyone recommend the way to help the simulation converged ? I tried to follow all instructions in the manual, but it still not converged.

By the way, I search how to model the free surface and I got three ways to do it as follow :

1. Define the surface as a wall and then put the Shear stresses to 0 for x and y.

2. Define the surface with symmetry boundary condition.

3. Use VOF model and set the surface as a pressure inlet.

Can anyone explain the differences between these boundary conditions ? or recommend which way is good for the water jet ?

Thank you for your kind attention.


Aravind September 26, 2004 18:14

Re: Boundary condition of free surface model

Can you define your problem more specifically? where is your pressure inlet, since your geometry is a pipe, do you mean to say that through one end of your pipe there is water coming in and flowing out through the other end into ambient atmosphere? right?


Tony September 27, 2004 00:45

Re: Boundary condition of free surface model
Hi Aravind,

Thank you very much for your kind attention.

Yes. It likes the water flowing out the pipe to the atmospere. At the flow inlet to the pipe, it is set to be Velocity_Inlet. At the atmosphere, the outlet of the pipe, I set it to Pressure_inlet on the top, while the bottom is symmetry and the other end is Pressure_outlet. Inside the pipe, it has two channels of water combining together before ejecting to the atmosphere. Now I used K-Epsilon for turbulent and VOF for free surface.

Please recommend me how to set the boundary condition. Am I right about the way to set the free surface ? As my first message, what is the difference between the three ways to simulate the free surface ?

Thank you very much in advance for your kindly help.

Sincerely yours,


Titiksh Patel September 27, 2004 13:48

Re: Boundary condition of free surface model

Can you tell me what is your domain, means what you are modellinn in addition to the pipe inlet.

For eg. a pipe filling a water tank, etc. Its your case is like this one.

I can give more details only after undertandinn your problem

Regards, Titiksh

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