[Zeng]

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!

[MuxaB]

Originally Posted by Zeng

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.

[Zeng]

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

[MuxaB]

hmm. is air modeled as compressible fluid?

[Zeng]

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....

[MuxaB]

Originally Posted by Zeng

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?

[mf_emp]

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