Recent developments on wall-bounded turbulence

The study of turbulence near walls has experienced a renaissance in the last decade, in part because of the availability of high-quality numerical simulations. The viscous and buffer layers over smooth walls are now fairly well understood. They are essentially independent of the outer flow, and there is a family of numerically-exact nonlinear structures that predict well many of the best-known characteristics of the wall layer, Such as the intensity and the spectra of the velocity fluctuations, and the dimensions of the dominant structures. Much of this progress was made possible by the increase in computer power that made the kinematic simulations of the late 1980s cheap enough to undertake conceptual dynamical experiments. We are today at the early stages of simulating the logarithmic layer. A kinematic picture of the various processes present in that part of the flow is beginning to emerge, and it is leading to a rough dynamical understanding. Some of it, surprisingly, in terms of linear models. Many processes mimic those in the buffer layer, but in an averaged LES sense, rather than applied to individual structures. The paper discusses the present status of our Understanding of this region, and possible future developments.