How to get reynolds stress values in POST CFX

syler3321 · July 19, 2010, 03:22

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

ghorrocks · July 19, 2010, 08:37

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, 04:47

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, 07:11

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, 07:15

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?

ahmed banna · January 1, 2017, 08:54

i was in the same situation and i think the following expression is useful
uiuj=-turbulent viscosity (dui/dxj+duj/dxi)
i have validated with some measured date and i was found a similar trend between them but different spatial values the simulated results was much lower .

July 19, 2010, 03:22	How to get reynolds stress values in POST CFX	#1
syler3321 Member ralph Join Date: Jun 2010 Location: Calgary Alberta Posts: 38 Rep Power: 16	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

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July 19, 2010, 08:37		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	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.

July 22, 2010, 04:47		#3
syler3321 Member ralph Join Date: Jun 2010 Location: Calgary Alberta Posts: 38 Rep Power: 16	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

July 22, 2010, 07:11		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	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).

July 22, 2010, 07:15		#5
artemiss1984 Member Join Date: Apr 2009 Posts: 38 Rep Power: 17	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.

March 17, 2011, 01:23		#6
Josh Senior Member Joshua Counsil Join Date: Jul 2009 Location: Halifax, Nova Scotia, Canada Posts: 366 Rep Power: 18	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?

January 1, 2017, 08:54		#7
ahmed banna New Member ahmed elbanna Join Date: Oct 2016 Posts: 7 Rep Power: 10	i was in the same situation and i think the following expression is useful uiuj=-turbulent viscosity (dui/dxj+duj/dxi) i have validated with some measured date and i was found a similar trend between them but different spatial values the simulated results was much lower .