The logarithmic region of wall turbulence: Universality, structure and interactions

The logarithmic region, also referred to as the inertial subrange in physical space, or the turbulent wall region, is arguably the most important region of wall-bounded turbulent flows due to the multi-scale processes that take place. In this paper we review recent studies that report on the universality of this region in terms of the scaling laws for the mean velocities and turbulence intensities. New high Reynolds number experimental data from a variety of flows are shown to be consistent with universal von Kármán and Townsend-Perry constants. This is in support of classical theory but contrary to the prevailing view that has emerged over the past decade or so. The nature of the logarithmic region is further discussed in terms of large and very large superstructures, and their role in interacting across the boundary layer is considered, with particular emphasis on their role in modulating and altering the fluctuating wall-shear stress.