Introduction: scaling and structure in high Reynolds number wall-bounded flows

According to Lighthill (1995), Prandtl's (1904) boundary layer has had the same transforming effect on fluid dynamics as Einstein's 1905 discoveries had on other parts of physics, which, by the way, were celebrated in 2005 as the World Year of Physics. That the boundary layer becomes turbulent was formally known to Blasius (1908), though, of course, the origin of turbulence in a pipe was studied earlier by Reynolds (1883). The problem of the turbulent boundary layer has since been a paradigm in the field of turbulence. Its practical importance in flows over air and water vehicles as well as in geophysical fluid dynamics has been recognized for nearly a century now. Advances in our understanding of the boundary-layer scaling and structure can be expected to shed further light on the complex and multiscale flow dynamics, and also offer basic input to flow control strategies for practically relevant problems such as reducing large vehicle drag (and hence, by implication, emission levels).