CHARACTERIZATION OF FIBER SUSPENSIONS IN ARCHETYPAL FLOWS BY MEANS OF STANDARD AND HIGH SPEED PARTICLE IMAGE VELOCIMETRY

Multiphase flows, i.e. flows in which one or more phases are dispersed within a carrier phase, are often encountered in environmental and engineering applications. The inherent di ffculty in studying these flows, due to the phases interactions, is further complicated when the carrier flow is turbulent. A speci c category of two-phase flows relevant for industrial applications is represented by flows where the shape of the dispersed phase is best approximated by rods or fibers, rather than spheres. In this thesis dilute fi ber suspensions in a turbulent pipe jet and in a channel with backward-facing step are characterized experimentally by means of standard and high-speed Particle Image Velocimetry. A full characterization of the near fi eld region of the single-phase, unladen jet is provided with a focus on entrainment rate. To this end, a simple model is presented to predict entrainment rate and tested against experimental data in the Reynolds number range [3200-28000]. The fiber-laden case is obtained by adding Nylon fi bers featuring an aspect ratio of 13.3 to the pipe jet at two diff erent concentrations at a Reynolds number equal to 10000. A phase discrimination technique is presented and validated to obtain simultaneous carrier flow and dispersed phase velocity data. Jet mean and RMS of velocity measurements, velocity correlations and spectral data are discussed with a focus on turbulence modulation induced by the dispersed bers. High spatial resolution measurements of fiber suspensions in a channel with a backward- facing step are presented and discussed. The high spatial resolution and the use of an object-fi tting technique allow the identi fication and measurement of single fibers orientation within the flow. Fibers orientation and concentration data are compared to carrier flow velocity statistics. The results hint at an important role played by bers orientation and orientation anisotropy in turbulent modulation on the carrier phase.