Realizable k-epsilon model constants

GeonwooKim · January 12, 2016, 05:42

Hello, everyone.

I just start about Fluent and have a question about realizable k-epsilon model.

The realizable k-epsilon model constants classified into five.
(C2 epsilon, TKE Prandtl Number, TDR Prandtl Number, Energy Prandtl Number
and Wall Prandtl Number)

I want to know that
1. when do I change the that of constant?
2. How do I change the that of constant?
in the Fluent calculation.

Please, contact to me.

Thank you.

davidwilcox · January 14, 2016, 04:51

Before you go all trigger-happy changing the constants, make sure you have the appropriate boundary conditions, have carried mesh-independence tests, etc etc.
As far as the constants are concerned, you would need to be aware of how the turbulence model was developed (in your case the realizable k epsilon).

Just to give you an overview, the realizable k-epsilon was developed to improve the prediction of the k-epsilon with respects to negative Reynolds normal stressess. Negative normal stresses are non-physical but the standard k epsilon will give you negative ones especially in stagnation regions. In short, realizability here means satisfying the Cauchy-Schwarz inequality.

See what the constants affect by looking at the transport equations. Do they affect the production of turbulence? Do they affect turbulence diffusion or do they increase dissipation? Consider all these first

As to how you change them in Fluent, you can input the constants via the GUI page of the turbulence models. Refer to the manual ( more specifically, refer to the transport equations under theory guide) and see what constants equal what values and change accordingly.

January 12, 2016, 05:42	Realizable k-epsilon model constants	#1
GeonwooKim New Member GeonwooKim Join Date: Jan 2016 Posts: 3 Rep Power: 10	Hello, everyone. I just start about Fluent and have a question about realizable k-epsilon model. The realizable k-epsilon model constants classified into five. (C2 epsilon, TKE Prandtl Number, TDR Prandtl Number, Energy Prandtl Number and Wall Prandtl Number) I want to know that 1. when do I change the that of constant? 2. How do I change the that of constant? in the Fluent calculation. Please, contact to me. Thank you.

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January 14, 2016, 04:51		#2
davidwilcox Senior Member david Join Date: Oct 2012 Posts: 142 Rep Power: 13	Before you go all trigger-happy changing the constants, make sure you have the appropriate boundary conditions, have carried mesh-independence tests, etc etc. As far as the constants are concerned, you would need to be aware of how the turbulence model was developed (in your case the realizable k epsilon). Just to give you an overview, the realizable k-epsilon was developed to improve the prediction of the k-epsilon with respects to negative Reynolds normal stressess. Negative normal stresses are non-physical but the standard k epsilon will give you negative ones especially in stagnation regions. In short, realizability here means satisfying the Cauchy-Schwarz inequality. See what the constants affect by looking at the transport equations. Do they affect the production of turbulence? Do they affect turbulence diffusion or do they increase dissipation? Consider all these first As to how you change them in Fluent, you can input the constants via the GUI page of the turbulence models. Refer to the manual ( more specifically, refer to the transport equations under theory guide) and see what constants equal what values and change accordingly.