Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session E37: Particle-Laden Flows: Non-Spherical Particles |
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Chair: Sarma Rani, University of Alabama, Huntsville Room: Georgia World Congress Center B409 |
Sunday, November 18, 2018 5:10PM - 5:23PM |
E37.00001: Density distribution effects on the settling dynamics of nonspherical inertial particles at intermediate Reynolds numbers Brandon R Angle, Matthew J Rau, Margaret L Byron Many settling, large, nonspherical particles of interest (e.g. naturally occurring aggregates) do not have a uniform density. Here we investigate the orientation and terminal velocity of freely falling uniform- and compound-density cylinders with relatively low aspect ratios (from 1 to 4) at intermediate Reynolds numbers (on the order of 100). Agarose gel with varying density and aluminum molds were used to fabricate hydrogel cylinders. All cylinders had an average specific gravity (SG) of 1.005. Two layers of gel, one with a SG of 1.003 adhered to a second layer with a SG of 1.007, were used to create the compound-density cylinders. The cylinders were released at the top of a 56 cm tall hexagonal tank filled with still water and imaged simultaneously by two high-speed cameras. Two additional low-speed cameras captured the full trajectory of each cylinder along with their landing position. The terminal velocity, fall orientation, and landing site of the cylinders were recorded and periodicity in the settling behavior of each cylinder was analyzed. Preliminary results show significant differences in the settling characteristics of uniform- vs. compound-density cylinders. These results have large implications for predicting the settling behavior of naturally-occurring particles. |
Sunday, November 18, 2018 5:23PM - 5:36PM |
E37.00002: Shear-induced migration and orientation of rigid fibers in an oscillatory pipe flow Scott Strednak, Saif Shaikh, Elisabeth Guazzelli, Jason E Butler The distributions of fibers in suspension were measured during oscillatory flow within a circular pipe. The fibers were rigid and non-colloidal, and two aspect ratios (length L to diameter d ratios) were tested; the suspending fluid was viscous, Newtonian, and density matched to the particles. As with spheres in parabolic flows, fibers in the concentrated suspensions migrated toward the center of the pipe. The migration was similar for the fibers, irrespective of the aspect ratio, at the same dimensionless number density nL2d (n is the particle number density), rather than at the same volume fraction. The extent of migration was maximum at nL2d=0.84 for both aspect ratios. The orientation distribution of the fibers was spatially dependent. Fibers near the center of the channel aligned closely with the flow direction, while fibers near the pipe wall had an enhanced probability of aligning in the vorticity direction. Additionally, qualitative observations indicate that nematic crystallites of fibers form near the center of the tube for highly concentrated suspensions. |
Sunday, November 18, 2018 5:36PM - 5:49PM |
E37.00003: Dynamical and thermal behavior of depositing firebrands in a turbulent boundary layer Chandana Anand, Babak Shotorban, Shankar Mahalingam The motion and deposition of cylindrical shaped firebrands (embers) were investigated by Lagrangian tracking in a turbulent boundary layer, simulated by LES, in a previous study (Anand et al, IJMF, in press, DOI: 10.1016/j.ijmultiphaseflow.2018.07.012). The influence of turbulence on motion of firebrands was explored by calculating their turbulent dispersion and diffusion. Their deposition pattern was quantified by calculating the joint probability density function of their landing position coordinates. The previous study was based on a critical assumption: the firebrand mass was fixed. In the current study, this assumption is relaxed while accounting for thermal behavior of firebrands, e.g., firebrand temperature, which was neglected in the previous study. As hot firebrands fly, they exchange thermal energy with ambient through convection and thermal radiation while losing mass by pyrolysis and char oxidation. These effects are accounted for by solving mass and energy equations for each firebrand. Influence of turbulence on mass and temperature of firebrands, which are important factors in the ignition of the spot where they land, is investigated.
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Sunday, November 18, 2018 5:49PM - 6:02PM |
E37.00004: Non-isotropy of slip velocity in large negatively buoyant non-spherical particles in turbulence Margaret Byron, Evan A Variano For inertial particles in turbulent flows, the difference between the particle’s velocity and that of the surrounding fluid can be substantial. This “slip velocity,” though difficult to measure experimentally, is important in particle-laden flow, particularly for studies of turbulence modulation or sedimentation. We present experimental measurements of the slip velocity from simultaneous stereo-PIV of both the solid particle and the surrounding fluid. Our particles are cylindrical (aspect ratios 0.5-4), negatively buoyant (specific gravities of 1.003 and 1.006), and larger than the Kolmogorov scale (by 10-40 times). We find that the slip velocity is anisotropic, with significantly less slip in the vertical (gravity-coupled) direction. Slip velocity increases with particle mass density, even in the non-gravity-coupled directions. We find that aspect ratio barely affects mean particle rotation rate, but higher densities correspond to lower rotation rates. Lastly, we compare particle rotation rate to the surrounding fluid vorticity, hypothesize mechanisms for angular momentum transfer between the fluid and solid phases, and outline future studies to further distinguish between gravitational and finite-size effects on the motion of inertial particles in flow. |
Sunday, November 18, 2018 6:02PM - 6:15PM |
E37.00005: Orientations of High-Concentration Fibers in Turbulence Lee Walsh, Andrea Masi-Phelps, Greg Voth The alignment of anisotropic particles in fluids has proven to be both practically important and visually striking, such as in rheoscopic fluids used in experimental observation and visual art pieces (the Kalliroscope). At high concentrations, particle orientations approach a continuous field whose ordering may be dominated by particle–particle interactions, as in liquid crystals or active matter, but it may instead reflect an underlying orientational order in the flow itself. We study the orientation field of fibers in turbulent flows both experimentally and in numerical simulations. In a turbulent flow, stiff fibers usually align with their neighbors, tending toward local order. However, the orientation field develops thin regions with large gradient, and a fractal geometry. This yields an anomalous scaling in the orientation structure functions at small separations. We will also discuss our methods for tracking the three-dimensional positions and orientations of fibers at high concentration, using views from multiple high-speed video cameras. |
Sunday, November 18, 2018 6:15PM - 6:28PM |
E37.00006: Orientation patterns of non-spherical particles in turbulence Bernhard Mehlig, Lihao Zhao, Kristian Gustafsson, Rui Ni, Stefan Kramel, Greg Voth, Helge I. Andersson In experiments and numerical simulations we measured angles between the orientations of small spheroids in turbulence. Since turbulent strains tend to align nearby spheroids, one might think that their relative angles are quite small. We show that this intuition fails in general: the distribution of relative angles has heavy power-law tails, and the dynamics evolves to a fractal attractor despite the fact that the fluid velocity is spatially smooth at small scales. The fractal geometry depends on particle shape, and it determines the power-law exponents. This talk is based on: Zhao, Gustavsson, Ni, Kramel, Voth, Andersson & Mehlig, arxiv:1707.06037 |
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