Skin friction coefficient
The skin friction coefficient, , is defined by:
Where is the local wall shear stress, is the fluid density and is the free-stream velocity (usually taken ouside of the boundary layer or at the inlet).
For a turbulent boundary layer several approximation formulas for the local skin friction for a flat plate can be used:
1/7 power law:
1/7 power law with experimental calibration (equation 21.12 in ):
Schlichting (equation 21.16 footnote in )
Schultz-Grunov (equation 21.19a in ):
(equation 38 in ):
- Schlichting, Hermann (1979), Boundary Layer Theory, ISBN 0-07-055334-3, 7th Edition.
- von Karman, Theodore (1934), Turbulence and Skin Friction, J. of the Aeronautical Sciences, Vol. 1, No 1, 1934, pp. 1-20.
Someone should add more data about total skin friction approximations, Prandtl-Schlichting skin-friction formula, and the Karman-Schoenherr equation.