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-   -   about open channel simulation in flow-3 (http://www.cfd-online.com/Forums/flow-3d/27336-about-open-channel-simulation-flow-3-a.html)

Marco January 18, 2009 12:38

about open channel simulation in flow-3
 
Dear expert :

I want to simulate rectangle shape open channel in flow-3d. I have some questions.

1. When I set boundary conditions. It can set velocities versus time. Can I set fluid depths versus time or set discharge curve versus time? If it can be set where could I do that?

2. What did I set on top boundary condition(Z max) because top boundary is air. Did I set symmetry boundry? If that's true what did I sat anything?

3. There are two fluids in open channel. One is water one is the air. Did I set two fluids in global? If that's true what did I sat anything?

Thaks your help!


HC January 26, 2009 13:13

Re: about open channel simulation in flow-3
 
1. Yes, you can also set time-dependent fluid depth/discharge. When you open the boundary dialog, there is a fluid height button. Click on that, and you can put values in the table inside that dialog. Between two neighboring times, the fluid height would be linearly interpolated. The similar procedure also applies to volume flow rate boundaries. In the dialog with volume flow rate option checked, there is a button called "Volume flow rate". Click on that and follow the same steps.

2. If the water is not touching the top boundary in the simulation, yes, you can set the Zmax boundary to symmetry, or you can set it to the pressure boundary with fraction of fluid equal to 0.

3. If there is no strong interaction between the water and the air, meaning the air is not affecting the water flow, you may as well just use one fluid model to simulate the motion of water. In some cases, you may need to study the entrained air and there is air entrainment model available under the physics tab. For some others, users may need to use two-fluid option accordingly and it depends on the cases.

Fran February 2, 2009 12:22

Re: about open channel simulation in flow-3
 
Marco, In a same case we have we have set in the inlet a fixed height and FF=1. In the outlets a static pressure = 0. The upper BC is simmetry.

zandi December 22, 2012 15:40

Quote:

Originally Posted by HC
;93158
1. Yes, you can also set time-dependent fluid depth/discharge. When you open the boundary dialog, there is a fluid height button. Click on that, and you can put values in the table inside that dialog. Between two neighboring times, the fluid height would be linearly interpolated. The similar procedure also applies to volume flow rate boundaries. In the dialog with volume flow rate option checked, there is a button called "Volume flow rate". Click on that and follow the same steps.

2. If the water is not touching the top boundary in the simulation, yes, you can set the Zmax boundary to symmetry, or you can set it to the pressure boundary with fraction of fluid equal to 0.

3. If there is no strong interaction between the water and the air, meaning the air is not affecting the water flow, you may as well just use one fluid model to simulate the motion of water. In some cases, you may need to study the entrained air and there is air entrainment model available under the physics tab. For some others, users may need to use two-fluid option accordingly and it depends on the cases.

can you help me with how finding the amount of air content?! in post processing part

mf_emp January 11, 2013 12:53

Hi HC,
whould you mind tell me what do you mean by "strong interaction between the water and the air, meaning the air is not affecting the water flow" ??
As i read before in an article two-fluid option didn't work for two phases like air & water, because of their great density diffrence. So it was written that we should use one-fluid, activating density evaluation & drift flux in physics tab.
but I'm not sure it works or not!!
http://hub.hku.hk/bitstream/10722/56029/3/FullText.pdf


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