title: Flow Scales of Influence on the Settling Velocities of Particles with Varying Characteristics.
abstract: The settling velocities of natural, synthetic, and industrial particles were measured in a grid turbulence facility using optical measurement techniques. Particle image velocimetry and 2D particle tracking were used to measure the instantaneous velocities of the flow and the particles' trajectories simultaneously. We find that for particles examined in this study (Rep = 0.4-123), settling velocity is either enhanced or unchanged relative to stagnant flow for the range of investigated turbulence conditions. The smallest particles' normalized settling velocities exhibited the most consistent trends when plotted versus the Kolmogorov-based Stokes numbers suggesting that the dissipative scales influence their dynamics. In contrast, the mid-sized particles were better characterized with a Stokes number based on the integral time scale. The largest particles were largely unaffected by the flow conditions. Using proper orthogonal decomposition (POD), the flow pattern scales are compared to particle trajectory curvature to complement results obtained through dimensional analysis using Stokes numbers. The smallest particles are found to have trajectories with curvatures of similar scale as the small flow scales (higher POD modes) whilst mid-sized particle trajectories had curvatures that were similar to the larger flow patterns (lower POD modes). The curvature trajectories of the largest particles did not correspond to any particular flow pattern scale suggesting that their trajectories were more random. These results provide experimental evidence of the "fast tracking" theory of settling velocity enhancement in turbulence and demonstrate that particles align themselves with flow scales in proportion to their size.
authors: School of Coastal and Marine Systems Science, Coastal Carolina University, Conway, South Carolina, 29528, United States of America.
authors: Corrine N
authors: CN
authors: Jacobs
authors: School of Coastal and Marine Systems Science, Coastal Carolina University, Conway, South Carolina, 29528, United States of America.
authors: Wilmot
authors: W
authors: Merchant
authors: School of Coastal and Marine Systems Science, Coastal Carolina University, Conway, South Carolina, 29528, United States of America.
authors: Marek
authors: M
authors: Jendrassak
authors: School of Coastal and Marine Systems Science, Coastal Carolina University, Conway, South Carolina, 29528, United States of America.
authors: Varavut
authors: V
authors: Limpasuvan
authors: School of Coastal and Marine Systems Science, Coastal Carolina University, Conway, South Carolina, 29528, United States of America.
authors: Roi
authors: R
authors: Gurka
authors: School of Coastal and Marine Systems Science, Coastal Carolina University, Conway, South Carolina, 29528, United States of America.
authors: Erin E
authors: EE
authors: Hackett
mesh_terms: D010316:Particle Size; D012212:Rheology / Q000379:methods*; D013501:Surface-Active Agents / Q000737:chemistry*; D055682:Viscoelastic Substances / Q000737:chemistry*
chemical_list: D013501:Surface-Active Agents; D055682:Viscoelastic Substances