AbstractThe thesis aims to study experimentally the effects of addition of solid, neutrally buoyant, spherical particles on the transition to turbulence in dilute particle-laden pipe flows. To this end, a pipe flow facility was designed and built with extreme care such that it precisely sets the flow rate using a piston-cylinder arrangement. Transition to turbulence was achieved using a perturbation system consisting of a single, impulsive jet orthogonal to the flow. To diagnose
the flow, a bespoke, combined two-dimensional particle image velocimetry (PIV) & particle tracking velocimetry (PTV) technique was devised. This technique implemented known image processing methods to separate the solid (particle) and fluid (tracers) phases based on the particles’ sizes and optical properties. Using this unique optical diagnostics, the first-ever simultaneous velocity measurements of solid (Lagrangian) and fluid (Eulerian) were obtained.
Single phase experiments showed that transition could be achieved at much lower Reynolds number than previously recorded. The two-phase measurements were conducted for particle sizes of 150 μm & 425 μm in dilute particle volume fraction (≤ 5×10−3). The results of these experiments highlighted the role of the particle size, their concentration and the volume of perturbing jet on the flow stability. For smaller particles, the transition was triggered only by higher volume injection compared to single phase flow at same Reynolds number. In addition, at higher particle concentration transitional threshold for low volume injection shifted to higher Reynolds number. For larger particles, transition shifted towards lower Reynolds numbers with increasing particle concentration. Eulerian-Lagrangian velocity measurements further revealed more detailed features of the puffs and slugs. Slugs homogeneously distributed larger particles, and modified the homogeneous turbulence within itself in contrast to the slugs in single phase flow.
|Date of Award||Jul 2020|
|Supervisor||Chris Pringle (Supervisor) & Alban Potherat (Supervisor)|