Experiments on particle dispersion in a turbulent mixing layer

The dispersion of solid particles in a turbulent shear layer has been investigated experimentally to clarify the dominant factors which govern the particle motion in turbulent gas flow. Spherical glass particles were loaded at the origin of a two-dimensional mixing layer. Flow measurements were carried out by a modified laser Doppler anemometer which enabled the measurement of both particle and gas phase velocities and particle number density. The particle dispersion strongly depended on the ability of the particles to follow the motion of large-scale eddies and was well-classified by the Stokes number (St). The range of St values covered in the present study turned out to involve three different stages of particle dispersion. It was confirmed from the experiments (with 0.5 < St < 2.5) that the particle dispersion coefficients became larger than the eddy diffusivity of the gas phase, i.e. the particles in the developing shear layer dispersed more than the fluid phase.