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-   -   reynolds shear stress (http://www.cfd-online.com/Forums/star-ccm/74261-reynolds-shear-stress.html)

rory_the_king March 28, 2010 19:15

reynolds shear stress
 
How can I build a scalar scene for the Reynolds shear stress?I have to select some in the physics model?or something else?
In the field functions this stress doesn't appear!!!
I am using k-epsilon model or k-omega model for the turbolence!
Thanks to all!
Lorenzo

plaunie March 29, 2010 13:48

I think you have to write your own unless the RST model is activated. At least that's what I had to do.

here is what I had in 2D, it was supposed to give me a vector: RS[ii],RS[jj],RS[ij] but the last term [ij] is wrong as I wasn't sure how to get du/dy, or dv/dx (simply). I abandoned it as I had other more pressing things to work on.

[
2*$TurbulentViscosity*(grad(mag($$Velocity))[1])-(2/3)*$Density*$TurbulentKineticEnergy,

2*$TurbulentViscosity*(grad(mag($$Velocity))[2])-(2/3)*$Density*$TurbulentKineticEnergy,

2*$TurbulentViscosity*(grad(mag($$Velocity))[3])]


it came from http://www.cfd-online.com/Wiki/Bouss...ity_assumption
with StarCCM defining the strain rate tensor in eqn [306] (Search StarCCM Help)

If you come up with an answer though it would be helpful.

Josh July 8, 2010 16:25

Can't you just multiply the velocity correlations, e.g., uu, by the density? The velocity correlations are directly extractable from CFX-Post.


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