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-   -   Calculate CF (https://www.cfd-online.com/Forums/tecplot/96491-calculate-cf.html)

 Odusseas January 24, 2012 11:00

Calculate CF using Tecplot

Hi all

I am tring to calculate the cf in tecplot.

cf = 2*tau_wall/(density*free stream velosity**2)

Until now I have not found one way to calculate the τw(tau wall) in tecplot.

So I am thinking If it is possible to calculate Cf from the equations that i found in this site.

http://www.cfd-online.com/Wiki/Skin_...on_coefficient

 duri January 24, 2012 13:21

I think for turbulent case you can estimate u+ from y+ based on the model you are using. Once u+ is available estimate u* which is sqrt(shear stress/density). In case of laminar flow you need to export gradient at wall to tecplot that directly gives shear stress.

The formula given in that link is for flat plate in case of other geometry you can refer to Fluid Dynamic Drag by Hoerner.

 Odusseas January 26, 2012 06:52

Hi Duri

My final goals are to compute Cf,u+,y+

For Cf I have Cf = 2Tw/(rho*U_ref^2) where Tw = wall shear stress
Tw = mu*(dUp/dy) where Up = velocity parallel to the wall
So I need to compute Tw

For u+ I have u+ = Up/u* and u* = sqrt(Tw/rho)
So, I need also here the Tw

For y+ I have y+ = u*y/v
And I have the same problem here.

So For Cf,y+,u+ I need the Tw
I read the tecplot manuals but I didn't found samething relative to the Tw.
Do you know any other way to compute Tw from tecplot??
Can tecplot calculate this??