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-   -   Buoyancy production for species concentration (http://www.cfd-online.com/Forums/fluent/41126-buoyancy-production-species-concentration.html)

 George Gerber May 25, 2006 16:08

Buoyancy production for species concentration

I would like to know how FLUENT computes the buoyancy production term in the k-equation when buoyancy is created due to saline concentrations (in an incompressible fluid), instead of temperature variations. I am trying to model a saline gravity flow. My model consists of a uds-scalar equation, which represents saline concentration. I have one material "brine", whose density is computed from an udf. The user-defined function computes the density of the brine mixture, given the saline concentration. Operating density is set to that of water 1000kg/m3. I am getting qualitatively realistic flows, except I am unsure whether FLUENT actually accounts for buoyancy production. All the documentation describes buoyancy production from a thermal perspective. Buoyancy production for saline flows should be proportional to the mean concentration gradient. Does anyone knows if it computes the production correctly? Have someone obtained good results on gravity flows using species transport?

Regards George

 opaque May 25, 2006 16:56

Re: Buoyancy production for species concentration

Dear George,

I have not used Fluent.. However, the theory doc implies that for non-Boussinesq buoyancy model, the buoyancy production is computed from the mean density gradient. If you are computing the density from the composition, i.e including the saline concentration, you are fine. Otherwise, you are not getting any production due to buoyancy.

Read the doc section "Effects of Buoyancy in Turbulence for k-epsilon models" (11.4.5 for Fluent 6.2).

Good luck,

Opaque.

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