Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session E28: Particle-laden Flows: Non-spherical Particles |
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Chair: Greg Voth, Wesleyan University Room: F149 |
Sunday, November 20, 2016 5:37PM - 5:50PM |
E28.00001: Measurements of inertial range scaling in rotations of rigid particles in turbulence Greg Voth, Brendan Cole, Stefan Kramel We measure the rotation rate of 3D-printed particles with sizes spanning the inertial range in a turbulent flow between oscillating grids. Tetrads, composed of four slender rods in tetrahedral symmetry, and triads, three slender rods in triangular planar symmetry, are tracked in a flow with $R_\lambda=156$ and $R_\lambda=214$ using four high-speed cameras. Tetrads rotate like spheres and triads rotate like disks. Measurements of tetrads' solid body rotation rates as a function of particle size are direct measurements of the coarse-grained vorticity and provide a new way to measure inertial range scaling in turbulent flows. We observe Kolmogorov scaling for the mean square solid body rotation rate of tetrads, $\langle \Omega^2\rangle \propto r^{-4/3}$, extending earlier work on rods by Parsa and Voth (PRL 2014) to particles that do not experience preferential orientation. The theory is extended to higher moments and intermittent scaling, but experiments do not yet resolve intermittency corrections. For triads, the solid-body rotation rate is preferentially aligned with the particle orientation, and we find that the preferential alignment of these large planar particles is quite different than was previously observed for small tracer disks. [Preview Abstract] |
Sunday, November 20, 2016 5:50PM - 6:03PM |
E28.00002: Orientation statistics of non-spherical particles sedimenting in turbulence Stefan Kramel, Lydia Tierney, Wyatt Rees, Greg A. Voth, Udayshankar Menon, Anubhab Roy, Donald L. Koch We study the sedimentation of non-spherical particles in turbulence. The particle orientation is determined by a competition between inertial torques causing a preferential alignment and turbulence randomizing the orientation. The relative importance is quantified by a settling number $S_F$ defined as the ratio of the tumbling-rate from inertial torques and from turbulence. The experiments focus on the orientation statistics of particles formed from several slender arms, including fibers and particles with three arms in planar symmetry (triads), which allows us to study alignment of both fibers and disk-like particles. We measure the time-resolved 3D orientations of the particles along with the fluid velocity field around them in a vertical water tunnel. An active jet array with 40 individually controllable jets enables us to adjust the turbulence intensity and observe the transition from strongly aligned particles to randomized orientations as $S_F$ is decreased. Results are compared to simulations and theory based on slender body theory. [Preview Abstract] |
Sunday, November 20, 2016 6:03PM - 6:16PM |
E28.00003: Rotation of non-spherical particles in turbulence of neutral buoyancy and large size Evan Variano, Nimish Pujara, Ankur Bordoloi We explore the ways in which particle size and shape affects particle rotation. We consider rotation in the laboratory frame and in the particles’ local frame of reference. We use homogeneous isotropic turbulence whose Taylor microscale is similar to the particle size. Our data, as well as a new analysis of Stokes numbers, suggests that particle inertia prevents alignment with turbulent structures. The total angular velocity is nearly shape-independent, an observation which has been presented before. We offer an explanation for this behavior, based on an analysis of Jeffery’s equations for inertia-free point ellipsoids. [Preview Abstract] |
Sunday, November 20, 2016 6:16PM - 6:29PM |
E28.00004: Drag reduction in turbulent channel laden with finite-size oblate spheroids. Mehdi Niazi Ardekani Suspensions of oblate rigid particles in a turbulent plane channel flow are investigated for different values of the particle volume fraction. We perform direct numerical simulations (DNS), using a direct-forcing immersed boundary method to account for the particle-fluid interactions, combined with a soft-sphere collision model and lubrication corrections for short-range particle-particle and particle-wall interactions. We show a clear drag reduction and turbulence attenuation in flows laden with oblate spheroids, both with respect to the single phase turbulent flow and to suspensions of rigid spheres. We explain the drag reduction by the lack of the particle layer at the wall, observed before for spherical particles. In addition, the special shape of the oblate particles creates a tendency to stay parallel to the wall in its vicinity, forming a shield of particles that prevents strong fluctuations in the outer layer to reach the wall and vice versa. Detailed statistics of the fluid and particle phase will be presented at the conference to explain the observed drag reduction. [Preview Abstract] |
Sunday, November 20, 2016 6:29PM - 6:42PM |
E28.00005: Computational and Experimental Study of Spherocylinder Particles in Fluidized Beds Vinay Mahajan, Hans Kuipers, Johan Padding Non-spherical particle flows are often encountered in fluidized process equipment. A coupled computational fluid dynamics(CFD) and discrete element method(DEM) approach has been extensively applied in recent years to study these flows at the particle scale. However, most of these studies focus on spherical particles while in reality, the constituent particles are seldom spherical. Particle shape can significantly affect the hydrodynamical response in fluidized beds. The drag force acting on a non-spherical particle can vary considerably with particle shape, orientation of the particle, Reynolds number and packing fraction. In this work, a CFD-DEM approach has been extended to model a lab scale quasi-2D fluidized bed of spherocylinder (rod-like) particles. These particles can be classified as Geldart D particles and have an aspect ratio of 4. Numerical results for the pressure drop, bed height and solid circulation patterns are compared with results from a complementary laboratory experiment. We also present results on particle orientations close to the confining walls, which provides interesting insight regarding the particle alignment. Thus the capability of the CFD-DEM approach to efficiently account for global bed dynamics in fluidized bed of rod-like particle is demonstrated. [Preview Abstract] |
Sunday, November 20, 2016 6:42PM - 6:55PM |
E28.00006: On the preferential sampling of helicity by isotropic helicoids Luca Biferale, Kristian Gustavsson, Riccardo Scatamacchia We present a theoretical and numerical study on the motion of isotropic helicoids in complex flows. These are particles whose motion is invariant under rotations but not under mirror reflections of the particle. This is the simplest, yet unexplored, extension of the much studied case of small spherical particles. We show that heavy isotropic helicoids, due to the coupling between translational and rotational degrees of freedom, preferentially sample different helical regions in laminar or chaotic advecting flows. This opens the way to control and engineer particles able to track complex flow structures with potential applications to microfluidics and turbulence. [Preview Abstract] |
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