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k-w SST freestream values for w

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Old   October 27, 2015, 06:29
Default k-w SST freestream values for w
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Syed Aaquib Hazari
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Dear all,

I want to know the freestream values of the blending function for 'w' in k-w SST.

Additional details:

I am trying to simulate the k-w SST for a two phase channel flow on MATLAB and I am having problems obtaining the accurate blending function values.

The blending function is as follows:

arg1=min(max(sqrt(k)/(0.09*w*y),500*nu/(y^2*w),4*sigma_w_2*k/(CD*y^2))

F_1=tanh(arg1^4)

Where 'y' is the nearest distance to any surface,
sigma_w_2 is a closure coefficient
CD is the cross diffusion modification


The values of F_1 should be 1 for near wall (implying k-w is switched on) & 0 for freestream values (implying k-e is switched on. However, I am obtaining incorrect values for the function. After reading through the SST model Menter mentions about freestream values for 'w'. I do not know what these values are.

If anyone does please let me know.

Thanks!
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Old   March 16, 2016, 02:07
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Ashwani
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Hi,

Were you able to solve this issue ?

wr
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Old   March 16, 2016, 06:16
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Hi Ashwani,

I did manage to proceed ahead.
Can you be more specific?
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Old   March 17, 2016, 01:41
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Ashwani
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Hi,

How is the values of blending function calculated at the boundary faces. The value of sigma_k , sigma_omega in diffusion term of k-omega and turbulent viscosity at the boundary face requires the value of blending function. How to handle them?

Thanks and regard
Ashwani
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Old   March 18, 2016, 05:29
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Syed Aaquib Hazari
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Hi,

So, the values of omega at the boundary faces is, as given by Menter

At the wall boundary
omega=10*(6*nu/(beta_1(del_y)^2)
k=0

Where, nu is the kinematic viscosity of the fluid, beta_1 is a closure coefficient and del_y is the distance between the first two cells.

The values of sigma_k & sigma_omega are not calculated at the boundary, but in the interior.

The values of sigma_k & sigma_omega are obtained after the blending functions are calculated.

I hope this answers your question.

Regards
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