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-   -   how to calculate y+ (http://www.cfd-online.com/Forums/main/7143-how-calculate-y.html)

kat February 11, 2004 08:42

how to calculate y+
 
How do you calculate y+ and in which range should it be?

Tim February 11, 2004 09:46

Re: how to calculate y+
 
hi,

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

or

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

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

Good luck

Tim



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