Particle dispersion in a turbulent, plane, free shear layer

The particle dispersion mechanisms in an inhomogeneous, anisotropic, high Reynolds number, turbulent free shear flow are presented. Flow visualization, as well as laser attenuation and diffraction techniques, are used to characterize the evolution of the flow. It is shown that, at each downstream location, the spectral response of the particles to the coherent velocity field that develops in the layer as a result of a Kelvin–Helmholtz type of instability leads to a selective dispersion of the particles across the mixing layer. Furthermore, this particle dispersion layer is shown to be composed of a central core region, characterized by a small mean particle size and two external sublayers with considerably larger mean particle sizes. Finally, the experimental results suggest the dominant role played by the coherent, large scale vortical structure in the dispersion of the particles. Scaling arguments and simplified flow models supporting this hypothesis are also presented.