calculating rms Values(u'u',v'v',w'w',u'v' and u'w') in CFX

ansari.nazanin · June 2, 2016, 03:06

Could anyone please help me with calculating rms Values(u'u',v'v',w'w',u'v' and u'w') in CFX? Can it be done using SST models? If not, how can I calculate them? I have tested RSM model before and the results obtained from Reynolds stresses are not satisfactory! Is it possible at all? to get these values that are fair enough to compare to literature?

ghorrocks · June 2, 2016, 07:19

In SST it is assumed isotropic so u'u' = v'v' = w'w'. But I cannot recall exactly what it does for the curvature correction term in SST (if you have activated it) as that may depart from isotropy - I will let you look that one up to check it. For how to calculate these values look at any turbulence modelling text book such as "Turbulence Modelling for CFD" by Wilcox.

ansari.nazanin · June 2, 2016, 07:24

Dear Glenn,
thank you for your reply. I have studied the theory part of it for a while, but i am not sure for the method i used in CFX. For axample by the RSM method i calculated in CFD-Post:

urms= (√Reynolds Stress uu)/(ρ*V∞ )

but the calculated terms are far from the literature.
-My question is if it is the correct way to do that and if there are other exact methods that i do'nt know about?
-I have seen in literature that in some studies they are being used in SST model and the results are fair enough and that wondered me!
Is it ok in SS tmodel to use the TKE for calculation of the u'u', v'v' and w'w'?

June 2, 2016, 03:06	calculating rms Values(u'u',v'v',w'w',u'v' and u'w') in CFX	#1
ansari.nazanin New Member Nazanin Ansari Join Date: Sep 2013 Posts: 12 Rep Power: 12	Could anyone please help me with calculating rms Values(u'u',v'v',w'w',u'v' and u'w') in CFX? Can it be done using SST models? If not, how can I calculate them? I have tested RSM model before and the results obtained from Reynolds stresses are not satisfactory! Is it possible at all? to get these values that are fair enough to compare to literature?

June 2, 2016, 07:19		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	In SST it is assumed isotropic so u'u' = v'v' = w'w'. But I cannot recall exactly what it does for the curvature correction term in SST (if you have activated it) as that may depart from isotropy - I will let you look that one up to check it. For how to calculate these values look at any turbulence modelling text book such as "Turbulence Modelling for CFD" by Wilcox.

June 2, 2016, 07:24		#3
ansari.nazanin New Member Nazanin Ansari Join Date: Sep 2013 Posts: 12 Rep Power: 12	Dear Glenn, thank you for your reply. I have studied the theory part of it for a while, but i am not sure for the method i used in CFX. For axample by the RSM method i calculated in CFD-Post: urms= (√Reynolds Stress uu)/(ρ*V∞ ) but the calculated terms are far from the literature. -My question is if it is the correct way to do that and if there are other exact methods that i do'nt know about? -I have seen in literature that in some studies they are being used in SST model and the results are fair enough and that wondered me! Is it ok in SS tmodel to use the TKE for calculation of the u'u', v'v' and w'w'?