THE EFFECT OF VORTEX PAIRING ON PARTICLE DISPERSION AND KINETIC-ENERGY TRANSFER IN A 2-PHASE TURBULENT SHEAR-LAYER

The transport of heavy, polydispersed particles and the inter-phase tr ansfer of kinetic energy due to the viscous drag forces is measured ex perimentally in a turbulent shear layer. To study the effect of the la rge-scale vortex pairing event, the shear layer is forced simultaneous ly with a fundamental and subharmonic perturbation. It is shown that v ortex pairing plays a homogenizing role on the particulate field, but the amount of homogenization is strongly dependent upon the particle's viscous relaxation time, the eddy turnover time, as well as the time the particles interact with each scale prior to a pairing event. Thus, even though the smaller size particles become well-mixed across the l arge eddies, the larger sizes are still dispersed in an inhomogeneous fashion. It is also found that the kinetic energy transfer between the phases occurs inhomogeneously with energy being exchanged predominant ly in a sublayer just outside the region of maximum turbulence intensi ty. The kinetic energy transfer is shown to exhibit notable positive a nd negative peaks located beneath the cores and stagnation points of t he large-scale eddy held, and these peaks are shown to result from the irrotational velocity perturbations created by the vortices. This ene rgy exchange mechanism remains a prominent process as long as the Stok es number of the particles relative to the vortices is of order unity.