Dynamics of other particulate systems
R. S. Deng, C. H. Wang, and K. A. Smith, “Bubble behavior in a Taylor vortex”, Physical Review E, 73, 036306 (2006).
We present a study on the behaviour of air bubbles captured in a Taylor vortex formed in the annulus between two concentric cylinders. It is found that small bubbles stay either at certain locations near the vortex cores or in the outflow regions along the inner cylinder. If the bubbles of the same size are introduced, a variety of bubble structures (such as ring, chain, cluster, etc.) appears due to different mechanisms. For bubbles of non uniform size, orbit crossing of small and large bubbles is observed. Droplets and particles can also be captured in Taylor vortices, and these exhibit certain unique features.
Typical bubble structures recorded by the high-speed video camera (a) a 4-bubble chain wall bubbles; (b) a 110-bubble ring of vortex bubbles. The two subpanels in (a) and (b) show the schematic top view of a chain/ring with two and three bubbles, respectively. (c) and (d) shows the evolution of a clustering ring into one larger, but fewer, bubbles, with (d) being photographed 30 min later than (c). The while stripe on the inner cylinder is due to the illumination while the thin and thick dotted lines are inserted to delineate the inner cylinder and the inner wall of the outer cylinder, respectively.
Y.S. Wong, C.H. Gan, C.H. Wang, A. Ingram, X. Fan, Parker, D.J., and J.P.K. Seville. “Instabilities in Vertically Vibrated Granular Beds at the Single Particle Scale”, Physics of Fluids, 18, 043302 (2006).
The dynamics of granular motion have been studied in a vertically vibrated bed using Positron Emission Particle Tracking (PEPT), which allows the motion of a single tracer particle to be followed in a non-invasive way. The particle movement is closely correlated with the oscillation of the bottom plate. Two types of granular motion have been observed in beds with heap formation: convection and fluctuation. The effects of system parameters, including vibration amplitude, frequency and bed weight, have been studied. The particle cycle frequency was found to correlate well with the dimensionless acceleration. Cycle frequency appears to be inversely proportional to bed mass. The particle dispersion was determined by following the tracer particle trajectory. The system is highly anisotropic, as the horizontal dispersion is stronger than the vertical dispersion.
Tracer trajectory over certain time periods for case A (heap formation): a) Side view: t = 2124-2163 s; b) End view: t = 2164-2280 s; c) End view: t = 2281-2350 s; and d) Plan view: t = 2124-2350 s.
F. Y. Leong, K. A. Smith, C. H. Wang, ” Secondary Flow Behavior in Double Bifurcation Models”, AIChE Annual Meeting, Cincinnati, Ohio, 30th Oct – 4th Nov 2005.
The flow behavior in bifurcations is of great physiological importance. The secondary flow profile in double bifurcation model is shown to be remarkably different from single bifurcation model. Furthermore, numerical simulation has revealed the presence of new counter-rotating vortices, which are in opposite sense to the classical Dean’s vortices, at the near wall of the grand-daughter branches. Theoretical analysis of the simplified 2-D problem shows the importance of the ‘M-shaped’ velocity profile in the formation of new vortices. Secondary flow behavior is also visualized experimentally using PIV in a single bifurcation glass model. Novel reconstruction of the upstream velocity profile in a single bifurcation model allows for experimental verification of double bifurcation models. Good agreement has been observed for both experimental and simulation results.
Cross-sectional PIV results for RDT without splitter plate (Top) and with splitter plate in the parent tube (Bottom)