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how to calculate y+

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Old   February 11, 2004, 08:42
Default how to calculate y+
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How do you calculate y+ and in which range should it be?
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Old   February 11, 2004, 09:46
Default Re: how to calculate y+
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Y+ = Y/Nu * Utau

Y = distance from the nearest wall, Nu = Kinematic viscosity, Utau = skin friction velocity.

In the region nearest to the wall known as the viscous sublayer (Y+ <30) Utau is given by Newtons law -

Utau = sqrt((Mu*(du/dy))/rho)

Where Mu is dynamic viscosity = Nu*rho

rho - density

Outside the viscous sublayer the log-law is asssumed to aspply.

This states

U+ = (1/K) log(y+) + C


U+ = (1/K) Log(Ey+)

With K= von Karman constant = 0.41 C = 5.5 or E = 9

Good luck


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