Models for the viscous and buffer layers over smooth walls are reviewed. Much of the friction coefficient in wall-bounded flows depends on this near-wall region. 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 in terms of their unsteady bursting. Many of the best-known characteristics of the wall layer, such as the dimensions of the dominant structures, are well predicted by these models.
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