Coherent structures and turbulence

The present state of understanding of coherent structures is examined with attention focused on their spatial details and dynamical significance. The characteristic measures of coherent structures are discussed and it is emphasized that coherent vorticity is the crucial property. A general scheme for educing structures in any transitional or fully turbulent flow is presented. The role of coherent structures in aerodynamic noise generation is studied and it is argued that the structure breakdown process is the dominant mechanism of noise generation.