The reason of the substitution of Omega by S in the SST k-omega model?

huangxianbei · December 30, 2017, 21:22

Hi,all:
These days I was straggling in the SST model. As in Menter's paper:
1. Menter, F. R. (1993), "Zonal Two Equation k-ω Turbulence Models for Aerodynamic Flows", AIAA Paper 93-2906.
2.Menter, F. R. (1994), "Two-Equation Eddy-Viscosity Turbulence Models for Engineering Applications", AIAA Journal, vol. 32, no 8. pp. 1598-1605.
The eddy viscosity is defined as :
nut=a_1*k/max(a1*omega;Omega*F_2)
where the Omega represents the absolute vorticity. While in most applications such as in Ansys cfx, the eddy viscosity is defined as :
nut=a_1*k/max(a1*omega;S*F_2)
where S is the magnitude of strain rate.
Obviously, they are different.
Does anyone konws how to explain? Or the reason why the form is modified?

Xianbei

GregCFD · December 31, 2017, 00:29

CFX cites (as you've noted) the original work by Menter back in 1993 but actually uses the modified form from an update in 2003 (Menter, F. R., Kuntz, M., and Langtry, R., "Ten Years of Industrial Experience with the SST Turbulence Model," ) which you can find online if you search for the title. I had a quick look at the paper and no rational is given for the change from Omega to S, it might be given in some earlier presentation or maybe someone with more experience can help you out there.

As an aside I found this by checking the NASA Turbulence Modeling Resource page which has been great for comparing and finding citations for models as it lists many different models and their modifications e.g. it has 7 different SST models listed.

huangxianbei · January 1, 2018, 20:14

Hi, it's glad to receive your reply. All the information is very helpful. I read the paper your referred to and also some related papers by Menter, while still didn't find the reason. Maybe it's discovered in the applications that S performs better than Omega.

Thanks very much.

December 30, 2017, 21:22	The reason of the substitution of Omega by S in the SST k-omega model?	#1
huangxianbei Senior Member Huang Xianbei Join Date: Sep 2013 Location: Yangzhou,China Posts: 302 Rep Power: 13	Hi,all: These days I was straggling in the SST model. As in Menter's paper: 1. Menter, F. R. (1993), "Zonal Two Equation k-ω Turbulence Models for Aerodynamic Flows", AIAA Paper 93-2906. 2.Menter, F. R. (1994), "Two-Equation Eddy-Viscosity Turbulence Models for Engineering Applications", AIAA Journal, vol. 32, no 8. pp. 1598-1605. The eddy viscosity is defined as : nut=a_1k/max(a1omega;OmegaF_2) where the Omega represents the absolute vorticity. While in most applications such as in Ansys cfx, the eddy viscosity is defined as : nut=a_1k/max(a1omega;SF_2) where S is the magnitude of strain rate. Obviously, they are different. Does anyone konws how to explain? Or the reason why the form is modified? Xianbei

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December 31, 2017, 00:29		#2
GregCFD Member Join Date: May 2016 Posts: 38 Rep Power: 9	CFX cites (as you've noted) the original work by Menter back in 1993 but actually uses the modified form from an update in 2003 (Menter, F. R., Kuntz, M., and Langtry, R., "Ten Years of Industrial Experience with the SST Turbulence Model," ) which you can find online if you search for the title. I had a quick look at the paper and no rational is given for the change from Omega to S, it might be given in some earlier presentation or maybe someone with more experience can help you out there. As an aside I found this by checking the NASA Turbulence Modeling Resource page which has been great for comparing and finding citations for models as it lists many different models and their modifications e.g. it has 7 different SST models listed.

January 1, 2018, 20:14		#3
huangxianbei Senior Member Huang Xianbei Join Date: Sep 2013 Location: Yangzhou,China Posts: 302 Rep Power: 13	Hi, it's glad to receive your reply. All the information is very helpful. I read the paper your referred to and also some related papers by Menter, while still didn't find the reason. Maybe it's discovered in the applications that S performs better than Omega. Thanks very much.