Fundamental Aspects of Turbulent Shear Flows — Introductory Remarks

Abstract

The various papers in this section deal with different fundamental questions raised by the study of homogeneous or sheared turbulence. These questions concern firstly theoretical and experimental aspects of atmospheric (Schertzer and Lovejoy) and laboratory (Viets, Bethke and Bougine) flows, and in particular the nature of internal dynamics and intermittency. The other questions raised relate to modelling studies in the framework of either the probability density function (p.d.f.) (Anand and Pope), or two-point closure theories (Chollet), or, finally, one-point closure techniques (Janicka and Kollmann, Ettestad and Lumley, and Dekeyser and Launder). It is usually considered that modelling of the p.d.f. is most suitable for problems with highly non-quadratic mechanisms, like combustion, and that two-point closures can only be used for problems with oversimplified configurations allowing the assumption of homogeneity and isotropy. We shall see here that these two techniques are now beginning to be applied outside their initial restricted domain and are presently dealing with problems which a few years ago could only have been tackled by one-point closure models.