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-   -   Multi-species question (http://www.cfd-online.com/Forums/fluent/30076-multi-species-question.html)

L Owens July 24, 2002 12:05

Multi-species question
 
I have a novice question about Fluent's capabilities with calculating multiple species, single-phase flows. I've heard that the applicability is limited to species concentrations less than 0.8 or 0.9. Can that be true? Are surface tension effects considered?

Thanks for any info.

Laika July 25, 2002 03:32

Re: Multi-species question
 
species transport in no problem for Fluent.

Why would you have a species concentration of 0.95? In that case you let the main fluid be this species, and you track something with a concentration of 0.05.

Were do you encounter surface tension effects in a single-phase flow? There are only surface tension effects at the interface between two fluids. If you have such an interface, your flow is not single-phase.

Laika, still orbiting

L Owens July 25, 2002 10:19

Re: Multi-species question
 
For a given flow with multiple species I am imagining local regions of concentration that vary all over the map, with from 0 to 1 and everything in between. And by surface tension in single-phase flow, I'm thinking of something like oil-water type mixtures, where both are liquid phase, but surface tension surely drives the coalescing of oil pockets.

I know Fluent has a Volume-of-Fluid method and an Eulerian-Eulerian model and an Algebraic Slip Mixture Model, and I'm wondering if anyone can spell out the limitations on the various methods, i.e., why use VOF if you've got Eulerian-Eulerian? for processing time?

Laika July 26, 2002 03:35

Re: Multi-species question
 
Oil and water are immiscible. Therefore you cannot use species transport. Species transport simulations can't handle separation.

If you have a free surface to track, VOF is the only way.

If you're interested in small scale coalescing effects, you should go for eulerian-eulerian. Good results may require tuning and maybe sone UDF.

Laika, still orbiting


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