Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session L31: Particle Laden Flows V |
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Chair: Antonio Ferrante, University of Washington Room: 33B |
Monday, November 19, 2012 3:35PM - 3:48PM |
L31.00001: ABSTRACT WITHDRAWN |
Monday, November 19, 2012 3:48PM - 4:01PM |
L31.00002: Turbulent flow computations for high speed shock dominated flows with a one-equation turbulence model John Ekaterinaris High order accurate discontinuous Galerkin (DG) discretization of the compressible three dimensional Nervier-Stokes equations for hybrid-type meshes is carried out. A general finite element discretization framework is used for all types elements and all computations of the DG method are performed in the regular computational domain for the standard cubic element. Total variation bounded limiters are applied for the standard cubic elements of the computational domain to obtain resolution of three dimensional moving shocks. Three dimensional inviscid flow results for weak and strong shocks over two dimensional configurations showed excellent agreement with other numerical solutions and the experiment. The DG high resolution method is applied for the computation of a moving shock exiting from a cylindrical shock tube and subsequently reflecting from a wall at a distance from the shock tube exit. The Spalart-Almaras one-equation turbulence model is used to obtain turbulent flow solutions for shock dominated flows and near wall turbulence of high speed flow after the exit of the shock. Good agreement with the experiment is found. [Preview Abstract] |
Monday, November 19, 2012 4:01PM - 4:14PM |
L31.00003: Radiation-induced turbulence in particle-laden buoyant flows Remi Zamansky, Filippo Coletti, Marc Massot, Ali Mani Particle laden flows are of tremendous importance in oceanography, geophysics, meteorology, astrophysics, and process technology. In the presence of thermal radiation, non-uniformities in particle concentration result in local temperature fluctuations (spatial and temporal), due to the different absorptivity between dispersed and carrier phases. Under the influence of gravity or other acceleration fields, fluid motion is induced by buoyancy, altering the particle distribution and possibly inducing higher non-uniformities. Numerical simulations have been performed which illustrate this effect. It is shown that for a broad range of parameters a (e.g. radiation intensity, acceleration, density ratio and number density) feedback loop between the local particle concentration, the temperature fluctuations and the buoyancy forcing can create and sustain turbulence. Inertial particles are observed to cluster and create high temperature plumes. When the particle response time is comparable to the characteristic lifetime of the plumes, the system exhibits intense fluctuations of turbulent kinetic energy and maximum concentration. [Preview Abstract] |
Monday, November 19, 2012 4:14PM - 4:27PM |
L31.00004: Particle-laden turbulence subject to radiation Mohammad Hadi Pour Ansari, Milad Mortazavi, Ali Mani It is well established that particle-laden flows play an important role in numerous technological and natural processes. Although the effect of turbulence on particle concentration is well studied in the literature, little is known about particle-flow systems coupled with radiative heating. Radiation is an active ingredient in many of such systems, including clouds, concentrated solar thermal systems, and astrophysical processes. In these environments the carrier gas is typically transparent and radiation is primarily absorbed by particles. Preferential concentration of particles by turbulence leads to inhomogeneous heating of the mixture over a wide range of length scales. This provides dynamical loops that can alter/force the turbulence. When heating is intense, inhomogeneous expansion of the gas alters the flow. For non-intense heating, the induced buoyancy effect can force the turbulence when a gravitational field is present. We will present results from our calculations, using direct numerical simulation of coupled turbulence-particle transport, demonstrating these effects over a wide range of parameters. [Preview Abstract] |
Monday, November 19, 2012 4:27PM - 4:40PM |
L31.00005: Effect of initial cloud shape and orientation on particle dispersion in the accelerated flow behind a shock Sean Davis, Gustaaf Jacobs We discuss the particle-laden flow development of a cloud of particles with varying initial shapes in the accelerated flow behind a normal moving shock. The effect of initial aspect ratio of a rectangular and elliptical cloud shape as well as the cloud's angle of attack with respect to the carrier flow are considered. Computations are performed with an in-house high order weighted essentially non-oscillatory (WENO-Z) finite difference scheme based Eulerian-Lagrangian solver. Streamlined elliptical shaped clouds produce less particle dispersion in the cross stream as compared to blunt rectangular shaped clouds. Averaged and root mean square statistics of the particle coordinates versus time show that the cloud disperses less with decreasing aspect ratio. The global cloud statistics are comparable for an initially rectangular cloud rotated at 45 degrees as compared to an initially triangular cloud. From observations and statistics we conclude that a particle cloud behaves like a solid body obstruction in the flow at early times, while at later times the particles convect on their inertia. [Preview Abstract] |
Monday, November 19, 2012 4:40PM - 4:53PM |
L31.00006: Computational Meso-Scale Study of Representative Unit Cubes for Inert Spheres Subject to Intense Shocks Cameron Stewart, Fady Najjar, D. Scott Stewart, John Bdzil Modern-engineered high explosive (HE) materials can consist of a matrix of solid, inert particles embedded into an HE charge. When this charge is detonated, intense shock waves are generated. As these intense shocks interact with the inert particles, large deformations occur in the particles while the incident shock diffracts around the particle interface. We will present results from a series of 3-D DNS of an intense shock interacting with unit-cube configurations of inert particles embedded into nitromethane. The LLNL multi-physics massively parallel hydrodynamics code ALE3D is used to carry out high-resolution (4 million nodes) simulations. Three representative unit-cube configurations are considered: primitive cubic, face-centered and body-centered cubic for two particle material types of varying impedance ratios. Previous work has only looked at in-line particles configurations. We investigate the time evolution of the unit cell configurations, vorticity being generated by the shock interaction, as well as the velocity and acceleration of the particles until they reach the quasi-steady regime. [Preview Abstract] |
Monday, November 19, 2012 4:53PM - 5:06PM |
L31.00007: Segregation of particles in incompressible random flows:singularities, intermittency and random uncorrelated motion Michael Reeks, Elena Meneguz We report recent measurements of the segregation of small inertial particles advected via Stokes drag in an isotropic homogeneous incompressible turbulent flow using a full Lagrangian method (FLM) to calculate the compressibility of an elemental volume of particles measured along a particle trajectory. The flow field was generated by a random Fourier mode kinematic simulation (KS) and by DNS. Numerical results show that the average compressibility decreases continuously with time if the value of the Stokes number is below a threshold value ~1, indicating that the segregation continues indefinitely. We find that the probability distribution of the compression tends to a Gaussian distribution except in the wings due to the occurrence of singularities in the particle concentration which makes the process highly intermittent. The distribution of singularities over a fixed interval of time for a range of Stoke numbers is shown to be well approximated by a Poisson distribution. Finally, we show that the occurrence of singularities is related to the formation of caustics and the occurrence of random uncorrelated motion (RUM). [Preview Abstract] |
Monday, November 19, 2012 5:06PM - 5:19PM |
L31.00008: Heavy particles in compressible homogeneous isotropic turbulence Yantao Yang, Jianchun Wang, Yipeng Shi, Zuoli Xiao, Xiantu He, Shiyi Chen In this talk we study the problem of heavy particles advected by compressible homogeneous isotropic turbulence. We simulate the Eulerian field by a novel WENO-Compact hybrid scheme and track a million heavy particles simultaneously. The heavy particle obeys the dynamic equations $d\mathbf{r}/dt = \mathbf{v}$ and $d\mathbf{v}/dt=-(\mathbf{v}-\mathbf{u})/\tau$, where $\mathbf{r}$ is the location vector, $\mathbf{u}$ and $\mathbf{v}$ are the Eulerian velocity and the particle velocity, respectively. The Stokes number is defined by the relax time $\tau$ and Kolmogorov time scale $\tau_\eta$ as $St = \tau/\tau_\eta$. Our study is focused on the effects of the Stokes number on the statistical behaviors of the particles with fixed turbulent Reynolds and Mach numbers. Simulation results reveal that as the Stokes number increases, the intermittency of the particle acceleration weakens. For larger Stokes number, the particle trajectories become smoother, as evidenced by the PDF of trajectory curvature shifting towards smaller value. The particle concentration distribution will also be discussed by investigating the number density and the pair dispersion. [Preview Abstract] |
Monday, November 19, 2012 5:19PM - 5:32PM |
L31.00009: Direct numerical simulation of the erosion of particle beds Zachary Borden, Ludovic Maurin, Eckart Meiburg, Yuliya Kanarska, Michael Glinsky Any code that attempts to simulate large scale geophysical flows and their effect on topography needs a way to couple local flow properties to a rate of sediment erosion or deposition. But, the mechanisms responsible for a particle's entrainment from a sediment bed into a flow are poorly understood. To better understand these mechanisms, we employ two- and three-dimensional direct numerical simulations that use a Lagrange multiplier method to enforce solid body motion of, and no-slip boundary conditions on spherical particles within our domain. We apply our code to the configuration of a shear flow over a regularly or randomly packed bed of particles. Results from these simulations will be discussed, and in particular, we focus on the effects of Reynolds number, shear velocity, and initial packing fraction. [Preview Abstract] |
Monday, November 19, 2012 5:32PM - 5:45PM |
L31.00010: Particle Interaction in Stratified Fluids Arezoo Ardekani, Amin Doostmohammadi Hydrodynamics of many industrial and environmental systems is characterized by settling of suspended particles, interacting with each other and the surrounding fluid. Sedimentation of pollutants in the air and settling of marine snow particles in the ocean play an important role in several atmospheric and marine environmental processes. Hydrodynamics of these systems is markedly affected by the presence of vertical density variations that ubiquitously occurs due to temperature or salinity gradients in a fluid column. Despite the widespread implications of settling in stratified media, the fundamental mechanisms of particle interaction are not known to characterize the microstructure of stratified particulate systems. In a homogeneous fluid, a three-stage process, called ``drafting, kissing, and tumbling'', governs pair interaction of particles settling in tandem and explains the nonlinear behavior of particles in a particulate system. The pressure wake of the leading particle attracts the trailing particle. Upon collision of the particles, an unstable elongated body is formed and tumbles due to inertial effects. In a viscoelastic fluid, the elongated body settling along its long axis is stable and leads to chaining of the particles (drafting, kissing, and chaining). Our recent computational results reveal the role of density stratification on pair particle interaction. We use direct numerical simulations to fully resolve the particle-particle interaction in stratified fluids. The vital role of diffusivity of the stratified agent and the relative importance of inertial and buoyancy forces are investigated. [Preview Abstract] |
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