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Modifying a turbulence model?

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Old   March 30, 2016, 10:56
Default Modifying a turbulence model?
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Luke Cleaver
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Hi
Im trying to use a modified RNG model reccommended by Reboud et al. i don't know how to modify the formulas in CFX. so how would i do this?



Many thanks
Luke
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Old   March 30, 2016, 15:18
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You are trying to modify the RNG model using information from the k-w model. That is a risky proposition without careful validation.

Or, you mean to modify the k-w model as suggested (assuming the authors did the proper validation)
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Old   March 30, 2016, 15:41
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Thanks for replying
Used wrong image as thats for SST
this is what i need to modify RNG with.

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Old   March 30, 2016, 15:57
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After selecting the RNG model, open the Advanced Controls for the turbulence model setup, and overwrite the Eddy Viscosity value by your own CEL expression.

Hope the above helps,
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Old   March 30, 2016, 17:15
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Very much so
thank you
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Old   March 31, 2016, 09:51
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Does this look right to you?
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Old   March 31, 2016, 10:44
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Is your model single phase multicomponent material, or multiphase flow ?

For a single phase multicomponent material, the expression seems correct.

For a multiphase flow model, it is not clear what "density" means. If you intend to be the volume fraction weighted density, I would write it explicitly. That is, MyMixtureDensity = WaterVapour.Density * WaterVapour.Volume Fraction + ....

Hope the above helps,
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Old   March 31, 2016, 11:10
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It is a multiphase flow model and the "density" is the mixture of the 2 fluids.
Are you saying write a expression for that density? as
WaterVapour.Density*WaterVapour.VolumeFraction+Liq uidWater.Density*LiquidWater.Volume Fraction
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Old   March 31, 2016, 11:19
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Correct.. Just in case the software assumes fluid phase.
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Old   March 31, 2016, 11:22
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Okay will try that
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