INTERACTIONS OF PARTICLES AND MICROBUBBLES WITH TURBULENCE

Dilute, dispersed two-phase flows arise in many contexts ranging from solid particles or droplets in gas flows to bubbles in liquids. Many o f the flows of interest are turbulent, which presents a complex proble m to analyze or to determine the dominant physical processes contribut ing to the observed phenomena. Advances in experimental techniques hav e made it possible to measure directly turbulent and particle velocity fluctuations in dilute systems. This has provided a counterpart to ad vances in computational and analytical models and a basis on which to test these models. Three specific areas are considered: the fluctuatin g forces on an individual particle in an unsteady flow, the response o f a solid particle to a turbulent air flow, and the corresponding resp onse of a small bubble in turbulent liquid flows. Results from direct numerical simulations are presented for each of these, including the n onuniform distribution of particles generated by local instantaneous f eatures of the flow. The issue of turbulence modulation at low to mode rate void fractions is discussed.