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Old   February 22, 2017, 19:33
Default Turbulent length scale
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Can somebody confirm me that the turbulent length scale that we need to input as a inlet condition (with the turbulent intensity) corresponds well to integral scale l which is the size of the largest eddies and which is also to be found in this formula:

\eta/l=Re^{-3/4} where \eta is the Kolmogorov scale.

The reason I ask is that there is a lot of notation for turbulent length scale: l, l_t, L, L_t, etc.

Thank you for your help !
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Old   February 23, 2017, 02:12
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Uwe Pilz
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l is the length of the large eddies. It should not be larger than L (the size of the problem) of course. l can be guessed.

For pipe flows:

l=0.038 d

d is the hydraulic diameter, which is identical the diameter for round pipes. For rectangular ones:

d = 2 \frac{ab}{a+b}

For flow around / past bodies:

l = 0.07 L

L is the size of the problem, for cylinders and spheres the diameter, for other bodies the diameter of the flow directed area.
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