The uses of coherent structure (Dryden Lecture)

An evaluation is made of the most significant achievements to date in the development history of turbulent flow coherent structures, which are conceptually characterized in terms of 'celerity', topology, and the phenomena of the 'coalescence' and 'splitting' of the structure. Emphasis is given to the mixing layer, which is the flow type whose structure is sufficiently well understood to warrant attempts at its technical application to problems of mixing and chemistry. An attempt is made to identify conceptual and experimental obstacles to progress in work with such other technically important flows as the turbulent boundary layer. The roles played by flow structure in numerical simulations and in current work on the manipulation and control of turbulent flow are noted, together with recent developments which suggest that corresponding advances are imminent in turbulence modeling.