Favre averaged values

chris1980 · June 22, 2006, 10:27

I want to do RANS with variable density. The governing equations for my problem known but I was wondering how to treat the favre averaged values!

- Are the variables automatically favre averaged when using a compressible RANS-model?

- When the solver computes i.e. k,epsilon ... are these the Favre averged values which I get back?

As you can see I am a little bit confused with these averaging things.

grtabor · June 22, 2006, 11:13

Yes, and yes.

The point of Favre averaging is that it is a mathematical trick designed to get us back to the same form of the equations. We _know_ how to solve the NSE in the form

ddt(rho u) + div(rho u u) = ...

When we average this equation /\ we get

ddt(/rho u \) + ....

Favre averaging allows us to split /rho u\ into separate variables, getting back to where we started again. So, yes; when using a compressible RANS model, the variables will be by definition assumed to be Favre averaged.

Gavin

ayannath23 · July 14, 2012, 22:29

I'm simulating incompresible reacting flow case where RSM is used as turbulence model. I have doubt about what fluent is actually solving for my case. Whether Favre-averaged NSE or RANS averaged NSE.

Can anybody help ?

June 22, 2006, 10:27	I want to do RANS with variabl	#1
chris1980 Member chris book Join Date: Mar 2009 Posts: 85 Rep Power: 17	I want to do RANS with variable density. The governing equations for my problem known but I was wondering how to treat the favre averaged values! - Are the variables automatically favre averaged when using a compressible RANS-model? - When the solver computes i.e. k,epsilon ... are these the Favre averged values which I get back? As you can see I am a little bit confused with these averaging things.

June 22, 2006, 11:13	Yes, and yes. The point of	#2
grtabor Senior Member Gavin Tabor Join Date: Mar 2009 Posts: 181 Rep Power: 17	Yes, and yes. The point of Favre averaging is that it is a mathematical trick designed to get us back to the same form of the equations. We _know_ how to solve the NSE in the form ddt(rho u) + div(rho u u) = ... When we average this equation /\ we get ddt(/rho u \) + .... Favre averaging allows us to split /rho u\ into separate variables, getting back to where we started again. So, yes; when using a compressible RANS model, the variables will be by definition assumed to be Favre averaged. Gavin ykanani likes this.

July 14, 2012, 22:29	Favre or RANS averaged equations are used in incompresible reacting flow ?	#3
ayannath23 New Member Ayan Join Date: Nov 2010 Posts: 9 Rep Power: 16	I'm simulating incompresible reacting flow case where RSM is used as turbulence model. I have doubt about what fluent is actually solving for my case. Whether Favre-averaged NSE or RANS averaged NSE. Can anybody help ?

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