Abstract

The lectures on turbulent shear layers and wakes presented and discussed at the well-known Marseille Turbulence meeting in 1961 and the sequel fifty years later in 2011, at the same location provide an opportunity to review progress in understanding the mechanics of these flows over this period.  The initial discussion is based on the understanding in 1961 gained from prior work.  Emphasis is then placed on the subsequent experimental revelation of the large scale vortical structure found to be essential to understanding the mechanics of the turbulent shear layer.  Critical insight into the mechanics (dynamics) that determines the growth rate (the shear stress), for example, is provided by the vorticity equation and the Biot-Savart relationship.  Conclusions are drawn from the experiments and some unresolved questions posed.  This is followed by a discussion of plane wakes.  Four regions of the plane wake are identified and experimental results on the large scale structure are discussed.  Emphasis is placed on the vorticity and the vorticity fluxes which contribute directly to the derivative of the principal Reynolds stress. Results from numerical calculations offer new insights into the mechanics especially through the vorticity and vorticity fluxes which could not previously be measured.  For this case too, conclusions are drawn and outstanding questions posed.  Results from recent work on linear and non-linear stability ( for which there are exact solutions in the linear regime for idealized shear layers and wakes) also contribute to a mechanistic understanding.