Structure of turbulent shear flows - A new look

Abstract

For many years experimental research in turbulence was devoted to the measurement of various correlations and special functions which had evolved from the statistical theories and from engineering computing methods based on the hierarchy of Reynolds equations. A recent change in direction toward a more deterministic description of turbulent structure has been initiated by the discovery of large coherent structures in several turbulent shear flows. The new point of view suggests that with every shear flow (jet, boundary layer, mixing layer, etc.) is associated an identifiable, characteristic structure; the development of the flow is controlled by the interactions of these structures with each other. An understanding of their properties should give insight into actual physical processes in turbulent flows, such as entrainment, transport, mixing, noise production, gustiness, etc. and should lead to improved methods for analyzing and computing them. Experiments designed to study these properties are aided by recent developments in instrumentation technology such as computer-aided control of the experiments, but the venerable technique of flow visualization is still an indispensable aid.