Wall Turbulence and Turbulent Drag Reduction

Fluid flow turbulence is probably the last unsolved mystery of classical physics. Research groups are active all over the World with the double aim to accumulate ever more precise empirical knowledge (using a synergy of experiments and numerical simulations), and to frame this empirical knowledge into a consistent theory that may prove of predictive value for applications. Italian Mechanics strongly participates in this effort. Here progress is described in the comprehension of wall-bounded turbulence and the reduction of turbulent skin-friction drag, in their four aspects of the shape of the mean velocity profile, the statistics of turbulent fluctuations, devices of passive drag reduction and devices of active drag reduction. An inevitable bias will be seen for the topics to which the present authors have contributed directly, but these are also the results that we can more easily entice the reader with.