Correlating Friction Velocity in Turbulent Boundary Layers Subjected to Freestream Turbulence

A turbulent boundary layer was subjected to grid-generated freestream turbulence to study the effects of turbulent length scale and intensity on skin friction. The study emphasized the importance of the turbulent-to-viscous length scale ratio and focused on correlating skin friction without the use of conventional boundary-layer Reynolds numbers. The experimental data were characterized by small-scale freestream turbulence above boundary layers with momentum-thickness Reynolds numbers ranging from 225 to 2700. Freestream turbulence intensities varied from 0.1 to 8.0%. The turbulent-to-viscous length scale ratios spanned from 100 to 1000, and ratios of freestream turbulent length scale to boundary-layer momentum thickness ranged from 4 to 32. A new boundary-layer model was used to establish a skin-friction correlation that does not require knowledge of the momentum-thickness Reynolds number