CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)
-   FLUENT (https://www.cfd-online.com/Forums/fluent/)
-   -   VOF model - volume fraction residual question (https://www.cfd-online.com/Forums/fluent/48081-vof-model-volume-fraction-residual-question.html)

 Wim Heirwegh April 28, 2008 19:31

VOF model - volume fraction residual question

Hi,

let me first situate the problem i'm working on:

I'm moddeling a stirred cup filled with water in normal environment (air). There are no inlets and no outlets. I'm trying to simulate the vortex that's formed by stirring in steady state. For this I use following options: - VOF model with implicit formulation - PISO - Modified HRIC for volume fraction discretization - Presto for pressure discretization - Second order upwind discretization on others (momentum,...) - RNG k-epsilon turbulence model - but without 'implicit body force' treatment

Now at the start of my simulation the scaled Residual 'volume fraction of 2-phase' has the value 1.8e-5 and remains around this value the whole time. It doesn't converge like the rest of my parameters... When i check my results after convergence of the other parameters it gives strange results: there isn't any outlined interface between the two phases (water and air). Instead there is a gradual change of the volume fraction from 0.01 to 0.98 over a wide distance in the cup.

For me this result doesn't seem to respond to reality where you can clearly see one nice vortex in a stirred water cup.

Could this be a problem with the value of the 'vf-2phase' residual that remained constant? Or is there a flaw in my moddeling? If someone has any experience with the 'vf-2phase' residual that can give some pointers. Every comment is helpfull. I like to keep the simulation steady-state :)

thank you

 kk May 3, 2008 14:37

Re: VOF model - volume fraction residual question

try to patch water in part of the cup using adapt>region then see how it will behave be careful most VOF calculation depend mostly at the proper boundary condition and the proper way to start the slution with so you need a lot of choices.

 kk May 3, 2008 14:41

Re: VOF model - volume fraction residual question

try to see also the bowl tutorial it may be useful for you.

 Wim Heirwegh May 3, 2008 16:54

Re: VOF model - volume fraction residual question

Do you suggest to patch water with my current results and continue with the simulation?

Because I already patched water at the start of my simulation.

The first iteration my scaled 'vf-phase2' residu has a value of 2.1e-5 It stays around this value while velocity+continuity converges. (velocity residus starts at 2.0e0 and converge to 1e-7)

Maybe some extra information on my cup geometry: It's top is closed off. It's filled half water, half air. Because it's sealed off of the environment, I don't use any boundary conditions.

extra info on setup: I initialized a volume fraction of 0 over the whole domain. Then marked 50% with adapt->region and patched a volume fraction of 1. (maybe this is what i'm doing wrong? if you read section 23.2.4 of the help file, they advise not to initialize zones with 0 volume fraction for a steady case)

Comment or reactions are always welcome! :)

BTW: The bowl tutorial was the first thing i read before starting the setup of my simulation.

 Wim Heirwegh May 3, 2008 16:59

Re: VOF model - volume fraction residual question

it actually seems a very simpel problem... yust a stirred cup of water or coffee with your hand closing off the cup. I want to see if it makes much difference in vortex production and pressure distribution with your hand or not.

 emreg November 15, 2011 10:47

hi
i hav a problem just same with this.
residual vf-phase-2 appears allways zero during whole of the transient iteration
other residuals change meaningly.

i dont know why vf-phase-2 doesnt change
could u help me plz

 gajendra July 4, 2013 01:16

Please sir send me bowl tutorial...

 jamalf64 July 4, 2013 07:21

Quote:
 Originally Posted by gajendra (Post 437698) Please sir send me bowl tutorial...
I can send to you this tutorial. Please send to me your email

 Bhargav93 July 8, 2013 12:08

Can someone send me the bowl tutorial please ybhargav93@gmail.com thank u

 jamalf64 July 8, 2013 13:44

Quote:
 Originally Posted by Bhargav93 (Post 438500) Can someone send me the bowl tutorial please ybhargav93@gmail.com thank u
I sent that.
Best Regards

 All times are GMT -4. The time now is 12:17.