Available experimental data of the flat-plate turbulent boundary layer have been resurveyed with focussing primarily on the outer layer. An appropriate velocity scale for the outer layer was found to be the external velocity multiplied by the ratio ofdisplacement thickness to boundary layer thickness, rather than friction velocity. In terms of this new scaling, the velocity-defect profile shows an excellent similarity for Re _??_ 2500 (Re is the Reynolds number based on momentum thickness). The mean velocity is approximately proportional to a half-power of the distance from the wall over a significant portion of the outer layer. While there is a region in which the mean velocity shows log-linear variation, the slope of the logarithmic law appears to be dependent on the Reynolds number for Re _??_ (2-3) × 10⁴. The above-mentioned similarity does not hold in the lower Reynolds number range of Re _??_ 2000.

View full abstract