The near-wall structures of turbulent wallflows

Models for the viscous and buffer layers over smooth walls are reviewed. It is shown that there is a family of numerically-exact nonlinear Structures which account for about half of the energy production and dissipation in the wall layer. The other half can be modelled by the unsteady bursting Of those structures. Many of the best-known characteristics of the wall layer, such as the lateral spacing among the streaks, are well predicted by these models. The limitations of minimal models are then discussed. and it is noted that a better approximation is to represent the velocity streaks as 'semi-infinite' wakes of the wall-normal velocity Structures, both in the buffer and in the logarithmic layer. The consequences of this characterization on the causal relation between bursting structures are also briefly discussed.