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Old   May 2, 2013, 08:20
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Michael Bell
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Im currently studying the effects of jet flow in plunge pools which involves simulating firing a jet of water into an open surface water tank.

I am currently struggling to set up my boundary conditions for the tank and was wondering if anyone had any good pointers. I'm trying to use the VOF method but thus far have had no success.

Any help or points would be much appreciated.
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Old   May 2, 2013, 08:53
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I would go these boundary conditions:
-velocity or mass-flow inlet for the water jet
-pressure outlet for the ambient air
-wall for the pool wall

How do you plan to let the water leave the domain? Or do you want a rising surface / transient simulation?

Maybe write a bit more about your setup and post some picture. What do you have for meshing. Is it 3d or 2d?
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Old   May 2, 2013, 10:30
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The simulation is based on an actual experiment in which the water level remains constant so I've placed two outlets in the top corners of the tank. At the moment I have them as pressure-outlets. Do you think I should set them to outflow? I'm running the simulation in 2d and have currently have a 5mm sized quadrilateral mesh.

I'll attach an annotated screen shot of the tank.

The purpose of the simulation is to study the diffusion of the jet in the pool so once I have the initial tank set up I can easily vary the jets velocity and diameter.

Sorry for asking so many questions, this is the first time I have ever used the software. Thank you for your help so far.
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File Type: jpg Tank Sketch.jpg (65.0 KB, 15 views)
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Old   May 2, 2013, 10:37
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1) What means "free water surface" at the top? Is this some kind of boundary condition?
2) It looks like you have water everywhere inside your domain. Why do you want to use the VOF model?
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Old   May 3, 2013, 07:03
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By free water surface I mean that there is no rigid wall on the top of the tank and that the tank is open. I am unsure on what boundary conditions I should set that to?

As for the VOF I was unsure on the process and thought it might be a valid method for analysis.
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Old   May 3, 2013, 07:15
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VOF is a multiphase model. You only need it, if you want to have water and air inside your domain. If you have just water, there is no need to use it. So what do you plan?
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Old   May 3, 2013, 09:42
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For the purpose of my work the analysis does not need to be time dependent so therefore I will set my time to steady. Since the inlet jet is meant to be turbluent I will set viscous solver to k-epsilon. I will set my domain as water-liquid then focus on my boundary conditions.

Like you've previously mentioned, walls will be wall, inlet will be set to velocity-inlet and outlets set to outflow. I've read on other threads that I can set my water surface to wall and put the shear equal to 0 to simulate the water's surface. I will also try setting the surface to pressure-outlet.

Finally, I will initialize the model computing from the inlet and run my calculations.

What do you think of my method thus far?
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Old   May 3, 2013, 09:52
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Sounds good. I never use the "outflow" bc. Don't know why, but up to now pressure and velocity/massflow was the choice
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Old   May 3, 2013, 09:55
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Brilliant. Thank you for your help! I'll let you know how I get on.
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Old   May 3, 2013, 10:03
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I think I would try this:
pool.jpg
2phase VOF-flow. Don't know if that works, but it looks the most intuitionally to me.
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