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Old   May 8, 2012, 05:34
Default question about Nested Grid for two fluids
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I started a simple flow example:

rectangular block and make it partly nested
half water (depth=0.3m) and half air
a water flow with constant velocity comes from right boundary, u= 0.1 m/s

the simulation will be easily done if 'one fluid' is chosen, whether 2-d or 3-d. However, if I choose two fluids(water and air), while all the other condition and parameters exactly the same with one fluid situation, the errors will occur.

'convective flux exceeded stability limit' will soon come along. After 2 or 3 of them, excessive convection failures make calculation terminated. And only 4e-09 second is calculated.

I'm stuck....I need advice. Thank you!
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Old   May 10, 2012, 21:10
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michael barkhudarov
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Quote:
Originally Posted by Zeng View Post
I started a simple flow example:

rectangular block and make it partly nested
half water (depth=0.3m) and half air
a water flow with constant velocity comes from right boundary, u= 0.1 m/s

the simulation will be easily done if 'one fluid' is chosen, whether 2-d or 3-d. However, if I choose two fluids(water and air), while all the other condition and parameters exactly the same with one fluid situation, the errors will occur.

'convective flux exceeded stability limit' will soon come along. After 2 or 3 of them, excessive convection failures make calculation terminated. And only 4e-09 second is calculated.

I'm stuck....I need advice. Thank you!
Is there an outlet at one of the mesh boundaries? For two fluids, if there is an inflow, there also must be an outflow.
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Old   May 10, 2012, 21:55
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yes, there is an outlet boundary~

the mesh is as followed:

block1
x:0~1.0, nxcelt=50, y:0~0.1, nycelt=5, z:0~0.5,nzcelt=25 ;

block2
x:0.5~0.8,nxcelt=30, y:0.02~0.08, nycelt=6, z:0.1~0.4, nzcelt=30 ;

Boundaries of block1 are:
right: V , left: O , front and back: S , bottom:W , top:P ;
for block2 they are all Symmetry
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Old   May 10, 2012, 23:24
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hmm. is air modeled as compressible fluid?
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Old   May 11, 2012, 00:00
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The flow mode is chosen as incompressible, so both two fluids are calculated as incompressible, right?

I thought that inter-block boundary type coefficient(alphamb) might affect, so I changed it from default to 0.5 or 1.0, but still didn't work....
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Old   May 19, 2012, 02:08
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Quote:
Originally Posted by Zeng View Post
The flow mode is chosen as incompressible, so both two fluids are calculated as incompressible, right?

I thought that inter-block boundary type coefficient(alphamb) might affect, so I changed it from default to 0.5 or 1.0, but still didn't work....
It is hard to figure out without seeing the problem. Have any ideas yourself?
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Old   May 27, 2012, 09:50
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Mahdiar Farhoudi
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That is exactly my problem too!
did you get what to do?
you can also check out:
Help > CUSTOM TUTORIALS > Hydraulics Tutorial > Variation: Run as a Two-Fluid Problem
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