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Y plus Calculation

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Old   January 31, 2017, 09:03
Exclamation Y plus Calculation
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Alejo
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Hello everyone,

I would like to know how Fluent calculates de Y+ parameter from the velocity field ? I know the definition of this parameter:

Y+ = U_tau * Y_node / Kinematic_Viscosity

With Y_node the distance from the center of the volumen to the wall; ans U_tau the friction velocity. This velocity is calculated as:

U_tau = (T_tau / Fluid density)^(1/2)

With T_Tau the wall shear stress. This value is deficed as:

T_Tau = Dynamic_Viscosity * (du/dy)_(y=0)

With (du/dy)_(y=0) the slope of the parallel velocity in the normal direction to the wall.

What I do not understand is how I could determine this derivate value at the wall if I only have the velocity field at the center of the control volume closet to the wall? Besides, when I am using a wall function I am far from the wall, so how can I obtain the value of the friction velocity?

Does Fluent use the log-velocity profile to define if the cell is in the sub-viscous layer or the turbulent layer ?

Best,

Alejandro
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friction velocity, log. velocity-profile, wall shear stress, yplus

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