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-   -   ATTENTION!! Validty of Fluent's VOF?? (http://www.cfd-online.com/Forums/fluent/33042-attention-validty-fluents-vof.html)

ozgur February 16, 2004 10:22

ATTENTION!! Validty of Fluent's VOF??
 
Hi all,

I am simulating free falling water drops (d=1-4 mm) in a surrounding media of supercritical CO2 (liquid like density, gas like viscosity). The terminal velocities I got so far are about 50 % lower than I expected. Moreover, the solution is highly dependent on the time step (an increase in the time step may result unpysical deformation, even the solution seems to converge!!) In addition, simulation is unstable for smaller drops, i.e. when the drop is 1mm, some strange velocity currents appear in the drop, which is not the case for bigger drops. (for all simulations diameter is resolved by 80 cells in 2D DP solver, time step btw. 10^-4 - 10^-5 s, geo-recon. scheme used, no turbulance model was employed)

After reading the article of C.W. Hirt (the founder of VOF) in http://www.flow3d.com/Cfd-101/whatsina.htm , I have a doubt that Fluent is able to make precise VOF calculations. He does not even call them (VOF in some commercial CFD codes, icluding Fluent) as VOF, but pseudo-VOF instead!!

What are the experience of the VOF users, regarding to validation of the simulation results?

One more thing. I think the following page gives a good summary of basic CFD concepts, which may be helpful for the CFD beginners (but it is so much filled up with the promotion of their Flow3D software):

http://www.flow3d.com/Cfd-101/cfd101.htm

mateus February 18, 2004 12:59

Re: ATTENTION!! Validty of Fluent's VOF??
 
Hi!

I had good expirience using VOF (fluent version 6.1, the version before did't work well) for dam break simulation, big drop falling into water... Problems occured with rising bubble where the solution was not phisical.

Best regards

MATEUS


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