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-   -   How to get reynolds stress values in POST CFX (http://www.cfd-online.com/Forums/cfx/78329-how-get-reynolds-stress-values-post-cfx.html)

syler3321 July 19, 2010 02:22

How to get reynolds stress values in POST CFX
 
Hello,
i am trying to find the values for the reynolds stresses in my 2d simulation in cfx 12. I used the k epsilon model and cant seem to find that option on CFX Post. Is there a way in which i can get the values for Reynolds Stress?

Thanks:eek:

ghorrocks July 19, 2010 07:37

The Reynolds Stresses can be evaluated from k and epsilon/omega. Look up any turbulence textbook and it will show the conversion. "Turbulence Modelling for CFD" by Wilcox is the one I use.

syler3321 July 22, 2010 03:47

Hi Glenn,
Thanks for the recommendation. It gave me some inkling about the reynolds shear stress but strangely enough, i was not able to match the reynolds shear stress uv with the experimental data despite getting good agreement on the mean velocity profile. uv = eddy viscosity*(du/dy+dv/dx). From CFX Post i can get the eddy viscosity. What's bugging me is that i'm not sure if du/dy is (velocityu.Gradient Y) because the reynolds shear stress uv differ a lot from the experimental data when i used that to get my shear stress.
please advice



Ralph

ghorrocks July 22, 2010 06:11

If you are within 50% of the experimental values of Reynolds stress you are close. It is diabolically difficult to measure this accurately and just as hard to simulate it accurately. Don't be too concerned if you are miles off. Concentrate on things like recirculation positions, drag, pressure drop or other things which can be measured more accurately and really count (for most engineering applications anyway).

artemiss1984 July 22, 2010 06:15

Dear friend.usually the Reynolds stress components obtained from RANS models have not good agreement with experimental data.if you are confident about the definition of uv in the software you should use more advanced models like LES to obtain good result for Reynolds stress components.

Josh March 17, 2011 01:23

I'm using the SST gamma-Re_theta model. I'm given the velocity correlations in Post, i.e., uu, uv, and vv (2D simulation).

Therefore, I should be able to specify the Reynolds stress as:

(u_i u_j) = uu + uv + vu + vv

Is this correct?


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