2 different time steps in Fluent's VOF??
Hi
i have red in Fluent's manual that in VOF, Fluent uses 2 different time steps. The first for the volume fraction equation, and the second for the rest of transport equations..... I didnt understood this at all Can anyone help please??? |
There is one timestep for the Navier-Stokes equations and one for the VOF-equation.
The VOF-equation is solved with a smaller timestep so it will be solved multiple times inside a single Navier-Stokes timestep. Thus you will get a stable solution for your interface without increasing computational times for pressure and velocity. |
Thank u a lot my friend.
I will allow myself to ask u some more questions please, and hoping it is not bothering u: 1-Is the interface reconstructed at each of those VOF time-steps (the small ones)??? or once each big time-step? 2-Why when i am solving in VOF model , Fluent does not plot residuals for Volume fraction equation????? Thank u and best regards |
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I'm familiar with the theory about VOF subcycles from OpenFOAM, but not from FLUENT. I'm afraid this is up to someone else who is more into FLUENT. |
If u can tell me how it is done in Opanfoam, it will be very good .
It must be done by a similar way in Fluent i think. thanks |
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And OpenFOAM is plotting residuals for the VOF-equation. Why do you bother? Something wrong with your calculations? |
Hi and thanks for ure answer. In fact i have a problem in my simulations, and i was trying to completely understand the VOF model to see if it can be due to the VOF model or to other things...
I will tell u my problem very brievly, and i hope that u can help... I am simulating a stratified gas-liquid flow in pipes. In simulations, the height of the liquid phase is always less than in experiments. I tried all turbulence models. The result are not very good, since the water velocity is overestimated and gas velocity underestimated, because of this problem. I tested on 2 diferent grids: same result. I tried to refine (adapt function in Fluent) the interface cells: same results. I the problem du to the VOF technique???? Thanks in advance for ure help |
This could really be anything, not only the VOF.
I suggest you start a new discussion special to your problem and give more details about the whole situation. |
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