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Shahed August 15, 2010 03:40

Multiphase region definition problem
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Hi everyone, i'm new to this board...

the simulation is a simple falling water in a tank under gravity force...

the geometry is a simple rectangular with two regions (it's a 2D mesh)... one on top, which is smaller and it's going to be defined as water. and the rest of the face is air. i want to simulate a transient flow for seeing how water actually falls down...

i define each domain in Basic Settings separately (the top region, Water and the bottom region, Air) but when I check it again, i surprisingly face that two regions are in the same phase!!

the question is how can i apply these settings to be sure that my each domains are in the specified phase that i want?...

it's part of my final project and i really need this help. i hope someone can give me the right direction.


ghorrocks August 15, 2010 06:47

Don't define the top region as a different domain. Make the entire thing one domain and use a function to define the air/water initial condition. A function setting the water volume fraction to something like step((z-height)/1[m]) will do it.

Also this flow is bound to be three dimensional. Your 2D results are going to be totally wrong. If you are just doing it to start off that is fine to get the simulation going, but be aware that for an accurate result it is going to be 3D.

Shahed August 15, 2010 07:01

thanks for the note. yes it's just a beginning for the case i'm studying...

but can you explain more specifically about the whole function thing? i haven't seen such menu's in CFX...

very appreciated

ghorrocks August 15, 2010 07:11

Have a look at the flow over a bump tutorial which gets installed with CFX. It is all one domain and an expression to set the air/water initial condition.

Shahed August 15, 2010 07:50

can you tell the exact name please, i can't find it. apparently the only multiphase flow in Ansys, CFX 12 is "Multiphase Flow in a Mixing Vessel"...

my final approach is to simulate a heat pipe by CFX... i've designed and almost constructed a heat pipe with all the details (heat-exchanger, a PCB for reading temperatures, etc... )

can i have your e-mail?
it would be great if i can use your advice

ghorrocks August 15, 2010 19:00

Have a look in the CFX documentation to find it. You will find the files for it in <CFX_ROOT>/examples.

Sorry, I don't give out my email address on the forum. If you have a question post it on the forum then you can get many people to help answer it. And only private message me if you actually have a private message for me - if it is a general question it should be posted on the forum.

Shahed August 16, 2010 03:33

yeah, i found it. it's Free Surface Flow Over a Bump
fair enough pal, i will post my questions here... Thank you

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