On the enhancement of boundary layer skin friction by turbulence: an angular momentum approach

Turbulence enhances the wall shear stress in boundary layers, significantly increasing drag on streamlined bodies. Other flow features such as free stream pressure gradients and streamwise layer growth also strongly influence local skin friction. In this paper, an angular momentum integral (AMI) equation is introduced to quantify these effects by representing them torques that alter shape of mean velocity profile. This approach uniquely isolates friction a Blasius single term depends only Reynolds number most relevant flow's engineering context, so other are interpreted augmentations relative laminar case having same number. The AMI for external flows shares key property with so-called FIK relation internal (Fukagata et al. , Phys. Fluids vol. 14, 2002, pp. L73–L76). Without geometrically imposed thickness, length scale may be chosen freely. After brief demonstration using Falkner–Skan applied diagnostic tool four transitional turbulent direct numerical simulation datasets. Regions negative wall-normal shown play role limiting peak during late stages transition, strengths terms become independent transition mechanism very short distance into fully regime. establishes intuitive, extensible framework interpreting impact turbulence control strategies