Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session AT: Multiphase Flows I |
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Chair: P. Bagchi, Rutgers University Room: Salt Palace Convention Center Ballroom FH |
Sunday, November 18, 2007 8:30AM - 8:43AM |
AT.00001: The Dynamics of Agglomerated Ferrofluid in Steady and Pulsatile Flows Alicia Williams, Kelley Stewart, Pavlos Vlachos Magnetic Drug Targeting (MDT) is a promising technique to deliver medication via functionalized magnetic particles to target sites in the treatment of diseases. In this work, the physics of steady and pulsatile flows laden with superparamagnetic nanoparticles in a square channel under the influence of a magnetic field induced by a 0.6 Tesla permanent magnet is studied. Herein, the dynamics of ferrofluid shedding from an initially accumulated mass in water are examined through shadowgraph imaging using two orthogonal cameras. Fundamental differences in the ferrofluid behavior occur between the steady and pulsatile flow cases, as expected. For steady flows, vortex ring shedding is visualized from the mass, and periodic shedding occurs only for moderate mass sizes where the shear forces in the flow interact with the magnetic forces. At Reynolds numbers below 500 with pulsatile flow, suction and roll up of the ferrofluid is seen during the low and moderate periods of flow, followed by the ejection of ferrofluid during high flow. These shadowgraphs illustrate the beauty and richness of ferrofluid dynamics, an understanding of which is instrumental to furthering MDT as an effective drug delivery device. [Preview Abstract] |
Sunday, November 18, 2007 8:43AM - 8:56AM |
AT.00002: Dissipative interactions between particles in shear flow Marina Popova, Peter Vorobieff, Marc Ingber, Alan Graham We present an experimental study of a low-Reynolds number shear flow carrying particles. The flow is nearly two-dimensional due to stable stratification of the fluid, with the particles occupying a planar neutral buoyancy layer. While both the two- and three-particle interactions show a degree of irreversibility, the three-particle interactions demonstrate apparently chaotic behavior, where small variations in the initial conditions of the experiment (i.e., particle positions) lead to large changes in the final state of the experiment. Moreover, a detailed knowledge of the trajectory of each particle in the triplet is required to relate the final particle order to the initial positions. Results of experiments with particles of different shapes (spherical, ellipsoid, etc.) are also discussed. [Preview Abstract] |
Sunday, November 18, 2007 8:56AM - 9:09AM |
AT.00003: Unsteady Forces on Particles in Compressible Flow Manoj Parmar, Andreas Haselbacher, S. Balachandar The acceleration of a body immersed in a fluid gives rise to so-called added-mass and history forces because some of the surrounding fluid is accelerated due to no-penetration condition and due to the developent of the boundary layer. These forces have been studied in detail, both theoretically and numerically, for incompressible flows and spherical particles. The purpose of the present investigation is to assess the effect of compressibility on these forces. Our primary interest is in strong accelerations of particles such as by impacting shock waves. Prior work investigated analytically unsteady forces on cylinders and spheres only using acoustic approximations at vanishingly small freestream Mach numbers. We extend this prior work to finite freestream Mach numbers and acceleration rates and compute numerically the unsteady forces for imposed accelerations. We find that the freestream Mach number and the acceleration rates have a strong effect on the unsteady forces. In contrast to incompressible flow, the unsteady force is not established immediately and the quasi-steady force coefficient is dependent on the acceleration rate. [Preview Abstract] |
Sunday, November 18, 2007 9:09AM - 9:22AM |
AT.00004: Lagrangian Simulations of Shock-Wave Diffraction at a Right-Angled Corner in a Particle-Laden Gas Andreas Haselbacher, Fady Najjar, S. Balachandar, Yue Ling The interaction between shock waves and particles is studied numerically using an Eulerian approach for the gas and a Lagrangian approach for the particles. Two examples of shock waves interacting with particles are studied. In the first, the interaction of a shock wave with a gas-particle interface and its subsequent deceleration to equilibrium conditions are investigated. Comparisons are made both to experimental data as well as theoretical predictions for the equilibrium conditions for the shock-wave Mach number as a function of position and spatial profiles in the relaxation region. Excellent agreement is found. The second example studied is the diffraction of a shock wave at a right-angled corner. Particular attention is focused on the flow field near the gas-particle interface. It is observed that vortical structures are formed at the gas-particle interfaces similar those found in shear-layer flows. [Preview Abstract] |
Sunday, November 18, 2007 9:22AM - 9:35AM |
AT.00005: Particle-turbulence interaction and sediment suspension from ripple beds in oscillatory flow Philip Knowles, Ken Kiger, Alberto Scotti An experimental sediment flume is used to investigate sediment transport mechanics within an oscillatory turbulent boundary layer over a mobile sediment bed in the ripple bed regime. Two-phase PIV is utilized to simultaneously capture data from each phase, allowing examination of suspension mechanisms, carrier phase stresses, and to obtain statistics to describe the momentum exchange between the phases. The technique employs median filtering, as well as size and brightness criteria to separate and accurately identify each phase. Independent well-conditioned tests have been conducted to improve the algorithm to account for the imaging conditions encountered in the vicinity of a mobile bed in order to minimize cross-talk between the phases and allow quantification of the dispersed phase concentration. Results show that large-scale vortical structures are responsible for the majority of sediment suspension from the bed. By examining the fluid stresses, it is found that a larger portion of the momentum transport is contained in the mean flow than in the turbulent fluctuations. Measurements of the conditional slip velocity between the phases show regions of large interfacial momentum transfer between the phases around the dune crests at flow reversal and maximum stream-wise velocity. [Preview Abstract] |
Sunday, November 18, 2007 9:35AM - 9:48AM |
AT.00006: Simulation of axisymmetric particle collision in a liquid environment Xiaobai Li, Melany Hunt, Tim Colonius Particle collisions in a liquid environment play an important role in the study of liquid-solid flows. This talk focuses on the collisional process and presents simulations of the coupled motion of a solid particle and surrounding liquid. The simulations use a multi-grid immersed boundary method with axisymmetric coordinates to investigate the normal collision between a rigid sphere and a wall. When the distance between the sphere and the wall decreases to a criteria value, a damping force based on elastohydrodynamic lubrication theory is introduced to reproduce the impacting and rebounding process. The model is compared with experimental measurements of the restitution coefficients for a range of Stokes numbers. The long term goal of this work is to develop collisional strategies that can be incorporated into simulations involving many particles in a viscous fluid. [Preview Abstract] |
Sunday, November 18, 2007 9:48AM - 10:01AM |
AT.00007: Non-intrusive methods for particle removal from smooth and rough surfaces Thomas Liebner, Gary Settles Previous researchers have characterized particle removal from a smooth surface as a function of the mean wall shear stress induced by the impingement of a turbulent air jet. We expanded upon this by an experimental study of particle removal at large standoff distances (and correspondingly low wall shear stresses) from both smooth and rough surfaces (APS/DFD 2006, GH007). The particle removal efficiency is now considered as a function of the induced wall shear stress, particle size, nozzle configuration, and impingement-surface properties. The behavior of the jet-impingement footprint size for shear stress sufficient to remove particles is considered. A range of particle sizes and surfaces is studied, with special emphasis on particle removal from fabrics. This is characterized in terms of the applied jet-impingement shear stress and the fabric thread spacing normalized by particle diameter. [Preview Abstract] |
Sunday, November 18, 2007 10:01AM - 10:14AM |
AT.00008: Lift \& drag correlations for a particle in wall-bounded linear shear flows at finite Re Fady Najjar, Lanying Zeng, S. Balachandar, Paul Fischer The lift and drag forces acting on a finite-sized rigid spherical particle are studied computationally using a high-order parallel spectral element method (Nek5000).We consider a wall-bounded linear shear flow in which the particle is embedded and the particle Reynolds number ranges from $2$ to $250$. The particle location is systematically changed from nearly sitting on the wall to far away from the wall. A drag correlation is proposed as a function of particle Reynolds number and separation distance from the wall. At very small separation distances, the lift force is observed to be positive and significantly larger at the entire Reynolds number range considered. However, at larger separation distances, the lift force becomes negative at some critical Reynolds number. At the largest separation distance considered, the lift coefficient shows a fairly good agreement with the numerical results of Kurose \& Komori (1999) in an unbounded linear shear flow. For particle on the wall, the lift coefficient shows a power law dependence on the particle Reynolds number in the finite Reynolds number regime. The numerical results compare very well with low Re theoretical results and a composite correlation that is accurate over the entire Re range is proposed. [Preview Abstract] |
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