Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session S28: Particle Laden Flows: Particle Resolved Simulations |
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Chair: Sarah Hormozi, Ohio University Room: 610 |
Tuesday, November 26, 2019 10:31AM - 10:44AM |
S28.00001: Cohesive Sediment in Turbulence Kunpeng Zhao, Florian Pomes, Raphael Ouillon, Thomas Koellner, Bernhard Vowinckel, Eckart Meiburg We investigate the balance between flocculation and break-up of cohesive particles in turbulent flows by means of grain-resolving direct numerical simulations. As a first step, we consider the model problem of inertial particles moving in a steady-state, cellular flow field consisting of counterrotating vortices. The dynamics of these particles are characterized by their Stokes number and Cohesion number, as well as by the ratio of their diameter to the vortex size. These one-way coupled simulations provide information on the competition between hydrodynamic, cohesive and collision forces, the equilibrium floc size distribution, and on the time scale of the floc formation process. We find that the equilibrium floc size grows with the Cohesion number, and that flocculation progresses most rapidly for a suitably defined Stokes number near unity. In a subsequent step, we explore how these findings translate to cohesive particles moving in homogeneous isotropic turbulence. [Preview Abstract] |
Tuesday, November 26, 2019 10:44AM - 10:57AM |
S28.00002: Interface-resolved simulations of small inertial particles in a turbulent channel flow Francesco Picano, Pedro Costa, Luca Brandt Turbulent flows laden with small inertial particles are found in different contexts. Dealing with very dilute conditions, the so-called one-way coupling regime takes place with particles transported by the fluid without back and mutual reactions. Even in this regime, models for particle dynamics are crucial to accurately simulate their transport. In this work, we compare data from interface-resolved and one-way-coupled point-particle direct numerical simulations (DNS) of a turbulent channel flow laden with small inertial particles, with high particle-to-fluid density ratio of 100 and particle diameter of 3 viscous units. The most dilute flow considered, solid volume fraction $O(10^{-5})$ shows the particle feedback on the flow to be negligible, whereas differences with respect to the unladen case are found for volume fraction $O(10^{-4})$. The most dilute case is taken as the benchmark for accessing the validity of usual point-particle model considering only a non-linear drag. In the bulk of the channel, particle velocity statistics from the point-particle DNS agree well with those from the interface-resolved DNS, while major differences are found close to the wall. We show that they are due to particle-wall interactions that are not reproduced by usual point-particle model. [Preview Abstract] |
Tuesday, November 26, 2019 10:57AM - 11:10AM |
S28.00003: Consolidation of freshly deposited cohesive and noncohesive sediment: Particle-resolved simulations Eckart Meiburg, Bernard Vowinckel, Edward Biegert, Paolo Luzzatto-Fegiz We analyze the consolidation of freshly deposited cohesive and noncohesive sediment by means of particle-resolved direct Navier-Stokes simulations based on the immersed boundary method. The computational model is parametrized by material properties and does not involve any arbitrary calibrations. We obtain the stress balance of the fluid-particle mixture from first principles and link it to the classical effective stress concept. The detailed data sets obtained from our simulations allow us to evaluate all terms of the derived stress balance. We compare the settling of cohesive sediment to its noncohesive counterpart, which corresponds to the settling of the individual primary particles. The simulation results yield a complete parametrization of the Gibson equation, which has been the method of choice to analyze self-weight consolidation. [Preview Abstract] |
Tuesday, November 26, 2019 11:10AM - 11:23AM |
S28.00004: Particle resolved simulations of a sphere settling in simple shear flows of yield-stress fluids Mohammad Sarabian, Marco E. Rosti, Luca Brandt, Sarah Hormozi We perform 3D numerical simulations to investigate the sedimentation of a single sphere in the absence and presence of a simple cross shear flow in a yield-stress fluid. In our simulations the settling flow is considered to be the primary flow, whereas the linear cross shear flow is a secondary flow. To study the effects of elasticity and plasticity of the carrying fluid on the sphere drag as well as the flow dynamics, the fluid is modeled using the elastoviscoplastic (EVP) constitutive laws proposed by Saramito. We find that the drag on the sphere settling in the absence or the presence of cross shear flow is an increasing function of material plasticity at constant elasticity, while it is a decreasing function of material elasticity at constant plasticity. Furthermore, the drag on a sphere settling in a sheared yield-stress fluid is reduced significantly as compared to an otherwise quiescent fluid. More importantly, the sphere drag in the presence of a secondary cross shear flow cannot be derived from the pure sedimentation drag law owing to the non-linear coupling of simple shear flow and the uniform flow. The total drag is decomposed into its components and we find that the form drag is the primary cause of drag enhancement by material plasticity in EVP fluid. [Preview Abstract] |
Tuesday, November 26, 2019 11:23AM - 11:36AM |
S28.00005: A penalization method for DNS of weakly compressible reacting gas-solid flows Baptiste Hardy, Juray De Wilde, Gregoire Winckelmans Gas-solid flows are encountered in many environmental and industrial phenomena. Simulating such flows at large scales requires closure models for interfacial mass, momentum and heat transfer. Particle-resolved simulations can support the development of improved closure laws, from first principles. The present study combines a penalization method to account for the solid phase with a weakly compressible approximation for the gas phase. Strong thermal effects from chemical reactions in the solid phase can induce significant density gradients near the particles and affect interfacial transfer laws. The present methodology handles general boundary conditions for the scalars: Dirichlet (Neumann) for infinitely fast (finite rate) surface reactions, and coupled heat and mass transfer description between the solid and fluid phases. A comparison with the incompressible case is also made to quantify the impact of density gradients. [Preview Abstract] |
Tuesday, November 26, 2019 11:36AM - 11:49AM |
S28.00006: Near-wall and collision dynamics of particles at a stagnation point on a wall Qing Li, Micheline Abbas, Jeffrey F. Morris, Eric Climent, Jacques Magnaudet We present highly resolved immersed boundary simulations of neutrally-buoyant sphere (radius $a$) motion in axisymmetric stagnation (Hiemenz) flow at a wall.Far from the wall, the particle behaves as a tracer, decelerated by the ambient pressure of the Hiemenz flow. Near the wall, slip velocity and `excess' hydrodynamic force (in addition to ambient pressure), $F_h$, play a role. Inertia is characterized by $a/\delta$ for boundary layer thickness, $\delta$; $F_h$ transitions at $a/\delta \approx 2$ to a form increasing strongly at the wall due to lubrication. The particle reaches $O(10^{-4}) a$ separations with $O(1)$ velocity, motivating a model for contact and rebound. Flow and collision are studied for one and two particles, with single particle motion dominated by lubrication pressure and hydrodynamic drag (latter toward the wall). For two identical particles on the axis, certain separations lead to particle collision before the lower (closer to wall) particle hits the wall; the resulting momentum exchange leads to larger impact velocity than for one particle. Dynamics of the colliding pair includes rebound without contact with the wall for the lower of two particles, due to sheltering by the upper particle from drag allowing the pressure force to dominate. [Preview Abstract] |
Tuesday, November 26, 2019 11:49AM - 12:02PM |
S28.00007: Rigid particle-laden flows computations with a distributed Lagrange multipliers/fictitious-domain method on an adaptive quad/oc-tree grid Can Selcuk, Stephane Popinet, Anthony Wachs Modeling rigid particle-laden flows requires an accurate description of the flow field in the close-vicinity of the particles (i.e. in the boundary layers). One of the numerical difficulties lies on the extremely fine grid necessary to fully capture the flow dynamic near the particle boundary (as e.g. lubrication force). In such scenario, fixed Cartesian grids are prohibitive as the required number of computational cells becomes impractical. To overcome this difficulty, we combine an adaptive mesh refinement (AMR) technique with a distributed Lagrange multipliers/fictitious-domain method (DLM/FD) (Glowinski et al. 1999). The solver is implemented within the code Basilisk (Popinet, 2015) which provides a set of adaptive-multigrid solvers on quad/oc-trees. The method is validated against various test cases involving spherical particles in different flow regimes: from Stokes flow to highly inertial flows. To compute flows laden with non-spherical particles, we couple our AMR-DLM/FD solver to the granular solver Grains3D (Wachs et al. 2012). With this numerical tool, the dynamics of multiple particles of complex shape freely moving in a fluid on adaptive quad/oc-tree becomes accessible. As an illustration, we present the case of $600$ free falling cubes in a large container. [Preview Abstract] |
Tuesday, November 26, 2019 12:02PM - 12:15PM |
S28.00008: Chaotic Orbits of Tumbling Ellipsoids in Viscous and Inviscid Fluids Erich Essmann, Prashant Valluri, Stephane Popinet, Rama Govindarajan It was shown that the equations of motions of an immersed tri-axial ellipsoid become non-integrable under certain inviscid conditions, (Kozlov and Onishchenko, 1982). Non-integrability is a necessary condition for chaotic dynamics. We used analytical and numerical methods to determine occurrence and conditions of chaotic orbits in viscous and inviscid environments for both tri-axial and prolate ellipsoids. Our numerical work uses Gerris (Popinet et al, 2003) augmented with a fully-coupled solver for fluid-solid interaction with 6 degrees-of-freedom (6DOF). For inviscid conditions, our numerical results agree with the solution of Kirchhoffâ€™s equations. Using recurrence quantification (Marwan et al, 2007) methods, we also characterise chaos and identify regime shifts from being periodic to chaotic. For inviscid systems, we observe chaotic behaviour only in the tri-axial systems and that chaos is a strong function of density ratio and the initial energy ratio. In viscous systems, we have noted evidence of chaotic orbits for symmetric ellipsoids. Due to vortex shedding behaviour in this context breaking the symmetry of the system. We show how chaos can be exploited under viscous environments to promote mixing. [Preview Abstract] |
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