# Extapolation of forces with wall laws.

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 October 7, 2002, 17:08 Extapolation of forces with wall laws. #1 Shu-Ren Hysing Guest   Posts: n/a 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.

 October 9, 2002, 03:55 Re: Extapolation of forces with wall laws. #2 versi Guest   Posts: n/a I guess the friction velocity of the wall law can give the wall shear.

 October 9, 2002, 11:36 Re: Extapolation of forces with wall laws. #3 Shu-Ren Hysing Guest   Posts: n/a 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?

 October 14, 2002, 04:46 Re: Extapolation of forces with wall laws. #4 sylvain Guest   Posts: n/a 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