Abstract

The last two decades have witnessed an intensifying
effort in learning how to manage flow turbulence: it has in
fact now become one of the most challenging and prized technological goals in fluid dynamics. The goal itself is of course not new. More than a hundred years ago, Reynolds already listed factors conducive to laminar and to turbulent flow (including among them curvature and acceleration). Furthermore, it is in retrospect clear that there were several early instances of successful turbulence management. Examples are the reduction in drag achieved with a ring-trip placed on the front of a sphere or the insertion of a splitter-plate behind a circular cylinder; by the early 1950s there were numerous exercises at boundary layer control. Although many of these studies were interesting and suggestive, they led to no spectacularly successful practical application, and the effort petered out in the late 1950s.