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Application of SST model by CEL

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Old   October 26, 2017, 15:59
Question Application of SST model by CEL
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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 e-mail(mosu2010@outlook.com).
thanks
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Old   October 26, 2017, 18:05
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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.
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Old   October 27, 2017, 04:22
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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.
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Old   October 27, 2017, 05:18
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Quote:
Originally Posted by ghorrocks View Post
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.
thanks for your reply.
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.
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Old   October 27, 2017, 05:21
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Quote:
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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.
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.
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Old   October 27, 2017, 05:52
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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.
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Old   October 27, 2017, 06:31
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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.
# State file created: 2017/10/27 18:22:19
# Build 17.1 2016.04.12-14.50-136032

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.
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Old   October 27, 2017, 06:55
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Please attach ALL the CCL. Not just the first bit.
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Old   October 27, 2017, 07:02
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Quote:
Originally Posted by ghorrocks View Post
Please attach ALL the CCL. Not just the first bit.
please check the attached files.
Attached Files
File Type: txt utsst.txt (18.0 KB, 7 views)
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Old   October 28, 2017, 06:15
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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?
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Old   October 29, 2017, 15:30
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Quote:
Originally Posted by ghorrocks View Post
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?
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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