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-   -   Extapolation of forces with wall laws. (http://www.cfd-online.com/Forums/main/5246-extapolation-forces-wall-laws.html)

Shu-Ren Hysing October 7, 2002 18:08

Extapolation of forces with wall laws.
 
Hi. Doe's anybody know if/how it is possible to extraplate the shear forces from the values obtained with k-epsilon wall laws in order to get more accurate lift and drag force calculations.

That is, I want to be able to obtain values of the forces directly at the walls even though I have used wall laws and thus don't have access to the values at the walls.

versi October 9, 2002 04:55

Re: Extapolation of forces with wall laws.
 
I guess the friction velocity of the wall law can give the wall shear.

Shu-Ren Hysing October 9, 2002 12:36

Re: Extapolation of forces with wall laws.
 
Well as I see it by using the friction velocity to get the shear stress you only get the value at y+=50 or so, and not at the actual wall where y+=0. Maybee there's not much difference, anybody that has experience with this?

sylvain October 14, 2002 05:46

Re: Extapolation of forces with wall laws.
 
u+ = sqrt(Tau_wall/rho) where Tau_wall is the shear at the wall.

Since you have y+ at point y, it comes :

nu*y+/y = u+ = sqrt(Tau_wall/rho)

This is under log law equilibrium hypothethis, otherwise....

Hope that helps,

Sylvain



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