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-   -   VOF for flow problems with inlet and outlet (http://www.cfd-online.com/Forums/fluent/40238-vof-flow-problems-inlet-outlet.html)

Jannifer March 21, 2006 04:34

VOF for flow problems with inlet and outlet
 
hello,

Anyone have any experience in using VOF model for flow in a channel before?

Would appreciate it if any one can offer any advice

Thanks

Charles March 21, 2006 10:56

Re: VOF for flow problems with inlet and outlet
 
What is it that you are struggling with?


jannifer March 22, 2006 03:03

Re: VOF for flow problems with inlet and outlet
 
hello

i am just simulating the flow of a slug bubble flowing in a mini channel. however i cannot get the expected bubble shape.

may i know whats the problems?

thanks for your help


Dustin March 28, 2006 10:19

Re: VOF for flow problems with inlet and outlet
 
Well, don't use outflow for one thing, it's not supported (even though you can select it).

Beyond that, use a fine mesh to render the interface well and a small enough time step (I usually have to use one less than the one suggested by the Cr=0.25 value).

Make sure to include surface tension...

jannifer April 4, 2006 03:38

Re: VOF for flow problems with inlet and outlet
 
Dustin

Thanks for your help

do you include wall adhesion?

also can u furnish me with more details for the model that i should use?

Do i use geo-reconstruct or implicit scheme. how about the ralaxation factor?

hope u can help me with this

Dustin April 4, 2006 06:40

Re: VOF for flow problems with inlet and outlet
 
- Usually, I try to run a simpler case without wall adhesion first, to make sure everything else is kosher, then I add the contact angle info in.

- Most of the time, Euler-Explicit with PISO, PRESTO and 2nd Order Momentum for VF and momentum work well for me.

- And I if I didn't mention before, try using as small a time step as is feasible.

- Relaxation factors should be fine as the default values, but you mayu need to lower momentum to 0.5 or so.

Good luck - Dustin


jannifer April 4, 2006 10:02

Re: VOF for flow problems with inlet and outlet
 
Heh thanks alot i will give it a try


Jannifer April 6, 2006 14:15

Re: VOF for flow problems with inlet and outlet
 
sorry to bother again

but can i check with you if VOF assumes that there no slip between the liquid and the gas phase.

Thank again

Dustin April 6, 2006 14:26

Re: VOF for flow problems with inlet and outlet
 
VOF averages the properties of the fluids over an interfacial region.

I would guess that's not the answer you want :)

- Dustin

Jannifer April 6, 2006 14:37

Re: VOF for flow problems with inlet and outlet
 
ya and a momentum equation is used for the entire domain.

But how can we intreprete the fact that the properties is being averaged? does that means that at the interfacial region the velocity of the gas and liquid phase are the same giving slip flow at the boundary?

Thanks in advance for your help


Dustin April 6, 2006 14:46

Re: VOF for flow problems with inlet and outlet
 
I'm shooting from the hip on this one, so it ain't gospel.

I think so (that the same wall slip velocity would be used at the interface). Contact angle/wall adhesion would dominate this process (I think) for most cases.

But, wrong may I be....

Jannifer April 6, 2006 14:56

Re: VOF for flow problems with inlet and outlet
 
haha okok thanks for your kind help.


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