Scaling of inner and outer regions for flat plate boundary layers

A new view of the scaling of the streamwise turbulence intensity profile is proposed for the zero pressure gradient turbulent boundary layer. The method is based on the scale decomposed streamwise velocity component, separated into a smalland a large-scale contribution using a wavelength pass-filter. This enables us to understand how large and small scale motions affect the streamwise turbulence intensity profile. It is found that the small-scale energetic content collapses remarkably well over a large range of Reynolds number (2800 ≤ Reτ ≤ 19000). On the other hand, the large-scale energetic content does not simply collapse in inner, outer or mixed scaling, but a clear peak emerges, which corresponds with the location of the spectral outer-peak. The peak location appears to follow the middle of the logarithmic layer, as well as the zero amplitude modulation location described by Mathis et al. [8]. The intensity of the outer-peak is found to grow much more rapidly than the innerpeak, as the Reynolds number increases, possibly supporting the controversial conjecture that at sufficient high Reynolds number, the outer-peak may overcome the inner-peak. Finally, this approach allows us to explore new scaling parameters for the streamwise turbulence intensity, potentially leading to more accurate formulation in flat-plate boundary layers.