|
[Sponsors] |
August 29, 2005, 22:31 |
VOF and strong surface tension effect
|
#1 |
Guest
Posts: n/a
|
Hi, CFD experts,
When applying VOF, what are the differences between strong surface tension effect and weak surface tension effect? That is: is cell quality more critical for strong surface tension effect? is there any special treatment needed for strong surface tension effect flow? .... etc. This is for micro-fluidics flows. Thanks! phsieh2005 |
|
August 30, 2005, 07:56 |
Re: VOF and strong surface tension effect
|
#2 |
Guest
Posts: n/a
|
When surface tension is weak (or geometry is large), you more or less have a single fluid -like problem with a jump in density and viscosity + some additional complications regarding the indicator (VOF) variable (I call it gamma), where you have to preserve the sharpness of the interface.
For cases where surface tension dominates, you get a different mode of coupling: the curvature of the interface (so, second derivative of the gamma equation) produces massive sources in the momentum equation - surface tension + the momentum solution prescribes the motion of the interface which changes the curvature. For small droplets, say 0.1-0.5 mm, this term may totally dominate the momentum equation, being several orders of magnitude larger. So, in the first case, you are dominated by the pressure-velocity coupling problem, while in the second you have massive velocity-gamma-pressure (you need pressure for continuity) coupling which is much nastier because of the curvature. If the curvature or the coupling is messed up, you will see "parasitic velocities" around the interface which either mess up the solution pretty badly or make it blow up. If you want to see an example of what I am talking about, try setting up a case with an air bubble in water with full density and viscosity ratio and a small diameter - this should tell you a lot about the VOF code you're using. Enjoy, Hrv |
|
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
modeling pipe flow with strong surface tension | phsieh2005 | OpenFOAM | 0 | August 27, 2009 14:51 |
about the numerical method for the free surface | ztdep | Main CFD Forum | 5 | May 1, 2006 17:09 |
How surface tension affect delta t? | Pei-Yng Hsieh | Main CFD Forum | 3 | February 25, 2005 11:55 |
VOF SURFACE TENSION EFFECTS | ozgur | FLUENT | 0 | March 26, 2004 04:36 |
Hirt's VOF algorithm for free surface flow | Anthony | Main CFD Forum | 10 | April 19, 1999 11:38 |