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October 26, 2017, 15:59 
Application of SST model by CEL

#1 
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linlin.geng
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S11=Velocity u.Gradient X
S12=0.5*(Velocity u.Gradient Y+ Velocity v.Gradient X) S13=0.5*(Velocity u.Gradient Z+ Velocity w.Gradient X) S22=Velocity v.Gradient Y S23=0.5*(Velocity v.Gradient Z+Velocity w.Gradient Y) S33=Velocity w.Gradient Z S21=S12 S23=S32 S31=S13 S=sqrt(2*S11^2+2*S12^2+2*S13^2+2*S21^2+2*S22^2+2*S 23^2+2*S31^2+2*S32^2+2*S33^2) a1=5/9 UtSST=Density*a1*Turbulence Kinetic Energy /max(a1 *Turbulence Eddy Frequency, S *Second Blending Function for SST model) The above CEL languages are applied to the CFX code to be the eddy viscosity of SST turbulent model. But the predicted results using the above CEL is not the same as the results predicted by the SST model. I do not know why, is it the CEL problem. If anyone knows why, please inform me in this forum or contact me with my email(mosu2010@outlook.com). thanks 

October 26, 2017, 18:05 

#2 
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Glenn Horrocks
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I have not checked your implementation in detail, and I have to assume that the simulation you are using to make this assessment is correct as well. In that case a possible explanation of the difference is the different way the function is coupled into the other equations. In the solver version of the SST model the turbulence equations are coupled into the solver tightly, but in CEL the coupling is looser. This means achieving convergence will be harder.


October 27, 2017, 04:22 

#3 
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Mr CFD
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Have you linearised your source terms? If you haven't read up a book by Patankar called Numerical Heat and Fluid Flow.


October 27, 2017, 05:18 

#4  
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linlin.geng
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Quote:
i also consider the situation as you think, but the fact that the big difference between these two method when i simulation the cavitating flows makes me confused, and can you give me some suggestions. thank you very much. 

October 27, 2017, 05:21 

#5 
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linlin.geng
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I just replicate the eddy viscosity of SST model by the CEL languages, so what does it have to do with the source terms. I do not understand. can you give me a clear explaniation. thank you very much.


October 27, 2017, 05:52 

#6 
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Glenn Horrocks
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Please attach the CCL of your simulation. To understand your results we will need to know how you have setup the model.


October 27, 2017, 06:31 

#7  
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Quote:
# Build 17.1 2016.04.1214.50136032 LIBRARY: CEL: EXPRESSIONS: S = 2^0.5*(S11 ^2+S12 ^2+S13 ^2+S21 ^2+S22 ^2+S23 ^2+S31 ^2+S32 ^2+S33 \ ^2)^0.5 S11 = water.Velocity u.Gradient X S12 = 0.5*(water.Velocity u.Gradient Y+ water.Velocity v.Gradient X) S13 = 0.5*(water.Velocity u.Gradient Z+water.Velocity w.Gradient X) S21 = S12 S22 = water.Velocity v.Gradient Y S23 = 0.5*(water.Velocity v.Gradient Z+water.Velocity w.Gradient Y) S31 = S13 S32 = S23 S33 = water.Velocity w.Gradient Z a1 = 5/9 utSST = Density *a1 *water.Turbulence Kinetic Energy /max(a1 \ *water.Turbulence Eddy Frequency, S *Second Blending Function for SST \ model) END END END COMMAND FILE: Version = 17.1 END Please check. Thank you very much. 

October 27, 2017, 06:55 

#8 
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Glenn Horrocks
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Please attach ALL the CCL. Not just the first bit.


October 27, 2017, 07:02 

#9 
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linlin.geng
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please check the attached files.


October 28, 2017, 06:15 

#10 
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Glenn Horrocks
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I note that this is a multiphase cavitation model. This adds a whole new dimension of complexity to the simulation.
How about you see if your function is the same as the built in SST model on a simpler single phase simulation? 

October 29, 2017, 15:30 

#11 
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linlin.geng
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yes, when i simulate the single phase using the SST model and the CEL of SST, the difference is very small. but in the case of cavitation prediction, the difference will be not negligible. May be the question of my CEL. i will check it in detail. thank you again.


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