The nature of turbulence

Turbulence research has always been torn between two objectives: the need to find engineering solutions to the myriad technical problems presented by turbulent flows, and the desire to gain a scientific understanding of the turbulence phenomenon. Because of these sometimes conflicting, sometimes complementary objectives, it is easy to lose a sense of perspective about fundamental turbulence research, where it has been, and where it is headed. In this paper, the history of the development of our ideas about turbulence is briefly traced with particular attention to self-preservation, local similarity, and coherent structures. Recent research on chaos in non-linear dynamical systems will be examined, and shown to provide a conceptual framework for the understanding of turbulence. In particular, it will be suggested that the attractors for the Navier-Stokes equations are the flows themselves. From this perspective, it will be argued that turbulence is the counterpart of the strange attractor, consequences of which are the observed tendencies toward self-preservation and coherent structures. (A)