Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session R28: Particle-Laden Turbulence II |
Hide Abstracts |
Chair: Nicholas Ouellette, Yale University Room: 2011 |
Tuesday, November 25, 2014 1:05PM - 1:18PM |
R28.00001: Flexible fibers in turbulent flows Gautier Verhille, Christophe Brouzet, Patrice Le Gal We describe, for the first time, an experiment devoted to the study of the spatial conformation of a flexible fiber in a turbulent flow. We propose a model for the transition from rigid to flexible regimes as the intensity of turbulence is increased or the elastic energy of the fiber is decreased. This transition occurs for a fiber typical length which is observed experimentally and recovered by our analysis. We also demonstrate that the conformations of flexible fibers in a turbulent flow are analog to conformations of flexible polymers in a good solvent. This last result opens some new and creative ways to model flexible fiber distortions in turbulent flows while addressing fundamental problems in polymer dynamics. [Preview Abstract] |
Tuesday, November 25, 2014 1:18PM - 1:31PM |
R28.00002: Preferential sampling of Lagrangian velocity gradients by tumbling rods in turbulence Rui Ni, Stefan Kramel, Nicholas T. Ouellette, Greg Voth Advances in fast stereoscopic imaging now allow us to study the motion of anisotropic particles in turbulent flow. But to get a complete picture of the tumbling dynamics of anisotropic particles, we need additional information from the surrounding fluid flow. Using a new scanning particle tracking system, we report simultaneous measurements of the tumbling motion of anisotropic particles and the velocity gradient of the flow near them, which provide a rich dataset with five scalars characterizing the velocity gradient tensor and two scalars describing the relative orientation of the rod. Using conditional statistics, we find that the squared tumbling rate of rod is small on average because the rod is preferentially aligned with the vorticity vector. It tends to be much larger, however, than its mean value when the rod is oriented at a particular angle with respect to the eigenvector of the strain-rate tensor corresponding to the smallest eigenvalue, because this particular orientation maximizes the contribution from both the vorticity and strain. [Preview Abstract] |
Tuesday, November 25, 2014 1:31PM - 1:44PM |
R28.00003: Simultaneous measurements of velocity gradients and tumbling motion of rods in 3D turbulence Stefan Kramel, Greg Voth, Rui Ni, Nicholas Ouellette The tumbling motion of anisotropic particles, advected in a fluid flow, is governed by the velocity gradient tensor. We have simultaneously measured the orientation of neutrally buoyant, rod-shaped particles and the velocity gradient tensor surrounding them in a 3D turbulent flow. We have built a scanning particle tracking velocimetry (SPTV) system, in which we illuminate a narrow slab of the detection volume and scan the illuminated slab through the entire detection volume, taking sequential images with four stereoscopic high speed cameras. The advantage of this technique over other PTV systems is that it enables us to increase the tracer particle concentration, because it removes many stereo-matching ambiguities, resulting in a high spatial resolution of the fluid velocity field. A trade-off is the decrease in temporal resolution. Our measurements of the tumbling rate of rods is in good agreement with Jeffery's equation, and this provides a good way to quantify the accuracy of the velocity gradient measurements. Reconstructed individual rod trajectories show the complex way that alignment with the vorticity and eigenvectors of the strain-rate tensor affect the tumbling rate. [Preview Abstract] |
Tuesday, November 25, 2014 1:44PM - 1:57PM |
R28.00004: Numerical Study of Explosive Dispersal of Particles Bertrand Rollin, Subramanian Annamalai, Christopher Neal, Thomas Jackson, S. Balachandar Recent experiments have shown that when a layer of solid particles is explosively dispersed, a multiphase instability front occurs, which leads to the formation of aerodynamically stable jet-like particle structures. We aim at replicating these experimental observations using highly resolved large-scale simulations, to improve our understanding of particulate front instabilities and jetting phenomenon. We consider a cylindrical core of high pressure and density gas generated from energetic material. Throughout the length of the cylinder, an annular region of micron-sized inert spherical particles surrounds the charge. The particles are treated as point particles, the gas is treated as a continuum, and a rigorous two-way coupled compressible multiphase formulation is used. The jets are believed to have their origin during the early phase of rapid acceleration of the bed of particles. Therefore, this work focuses on capturing the early-time behavior and growth of the instabilities caused by the presence of particles. The accuracy of our predictive simulations will be studied by comparing the shock radius, particle front location, and other relevant metrics against the data extracted from experimental results. [Preview Abstract] |
Tuesday, November 25, 2014 1:57PM - 2:10PM |
R28.00005: Drag measurements of shock accelerated particles Greg Orlicz, Adam Martinez, Kathy Prestridge The horizontal shock tube facility at Los Alamos is used to investigate the drag forces on micrometer sized solid particles dispersed in air when they are accelerated by a shock. Eight-frame, high-speed particle tracking velocimetry/accelerometry (PTVA) diagnostics are implemented to measure the trajectory of individual particles, and a shadowgraphy system measures the shock location during experiments. Incident shock Mach number, particle diameter, and particle density are varied. We compare the measured position, velocity and acceleration histories to those given by the quasi-steady drag approximation and other empirical unsteady drag models. Estimations of the drag coefficients are found to be higher than those for steady drag. Measurements at this facility will be used to further develop and validate empirical models of unsteady drag. [Preview Abstract] |
Tuesday, November 25, 2014 2:10PM - 2:23PM |
R28.00006: Formation of Bidisperse Particle Clouds Jenn Wei Er, Bing Zhao, Adrian W.K. Law, E. Eric Adams When a group of dense particles is released instantaneously into water, their motion has been conceptualized as a circulating particle thermal (Ruggerber 2000). However, Wen and Nacamuli (1996) observed the formation of particle clumps characterized by a narrow, fast moving core shedding particles into wakes. They observed the clump formation even for particles in the non-cohesive range as long as the source Rayleigh number was large (\textit{Ra}\textgreater 1E3) or equivalently the source cloud number (\textit{Nc}) was small (\textit{Nc}\textless 3.2E2). This physical phenomenon has been investigated by Zhao et al. (2014) through physical experiments. They proposed the theoretical support for \textit{Nc} dependence and categorized the formation processes into cloud formation, transitional regime and clump formation. Previous works focused mainly on the behavior of monodisperse particles. The present study further extends the experimental investigation to the formation process of bidisperse particles. Experiments are conducted in a glass tank with a water depth of 90 cm. Finite amounts of sediments with various weight proportions between coarser and finer particles are released from a cylindrical tube. The \textit{Nc} being tested ranges from 6E-3 to 9.9E-2, which covers all the three formation regimes. The experimental results showed that the introduction of coarse particles promotes cloud formation and reduce the losses of finer particles into the wake. More quantitative descriptions of the effects of source conditions on the formation processes will be presented during the conference. [Preview Abstract] |
Tuesday, November 25, 2014 2:23PM - 2:36PM |
R28.00007: ABSTRACT WITHDRAWN |
Tuesday, November 25, 2014 2:36PM - 2:49PM |
R28.00008: Experimental Studies of the Dynamics of Breakup for Immiscible Liquid Droplets in a Sheared Turbulent Flow Chin Hei Ng, Alberto Aliseda Breakup of a dispersed phase in a turbulent flow is a classical problem in multiphase flow with multiple applications to industrial and environmental processes. Most turbulent breakup models are inspired by Kolmogorov-Hinze theory, and assume the breakup is the result of the interaction between a droplet and an eddy of similar length scale. There are, however, conditions in which a droplet is stretched by the mean shear into long ligaments before break-up. The stretched droplet has a length scale larger than the inertial subrange, and collides with multiple eddies of different sizes that produce direct pinch off, or Raleigh-Plateau instability. We present experiments in which various immiscible liquids were injected in a well-characterized turbulent round jet at different Weber and Ohnesorge numbers. Droplet size distributions are compared to classical results from breakup dominated by surface tension system and to existing turbulent breakup models. Breakup characteristics, such as the breakup time and daughter particle size distribution, are obtained from breakup tracking of high-speed video images. The dependency of the breakup statistics on the relevant non-dimensional parameters that dominate the process are investigated. [Preview Abstract] |
Tuesday, November 25, 2014 2:49PM - 3:02PM |
R28.00009: ABSTRACT WITHDRAWN |
Tuesday, November 25, 2014 3:02PM - 3:15PM |
R28.00010: Critical Reynolds numbers for particle capture in Y-, T-, and arrow-shaped junctions Jesse Ault, Howard Stone, Daniele Vigolo, Stefan Radl Despite the prevalence of Y-, T- and arrow-shaped junctions in fluid flow networks, the flow behavior within these junctions is not yet fully understood. Vortical structures and vortex breakdown can lead to the unexpected trapping of particles within the junctions. In order to determine the flow regimes in which this phenomenon occurs, the critical Reynolds numbers for particle capture in a range of junction geometries are determined. These critical Reynolds numbers are sought experimentally for Y-, T- and arrow-shaped junctions with angles ranging from 10 110 degrees. Particle motion is visualized using a high-speed camera. OpenFOAM numerical simulations are performed for the same flows and the results are compared with the experimental measurements. The critical Reynolds numbers for capture as a function of the junction angle for various particle/liquid density ratios are plotted. The results demonstrate a maximum and minimum junction angle for which capture will occur, as well as an optimum junction angle for capture. Using these results, the capture phenomenon can be enhanced, or completely avoided, by selecting the appropriate flow geometry and Reynolds number. [Preview Abstract] |
Tuesday, November 25, 2014 3:15PM - 3:28PM |
R28.00011: Particle Deposition in a Two-Fluid Flow Environment Yit Fatt Yap, Afshin Goharzadeh, Francisco M Vargas, Chee Kiong John Chai The formation of particle deposit on surfaces occurs in many applications. For example, in the oil and gas industry, deposition of wax, hydrates and asphaltene reduces flows and clogs pipelines eventually if left untreated. Removal of the deposits is costly as it disrupts production. To further complicate the problem, the main flow carrying the depositing particles is often of a multi-phase nature. Successful mitigation effort requires good understanding and eventual prediction of the deposition process interacting within a multiphase flow environment. This work presents a model for prediction of particle deposition in a two-fluid flow environment. Modeling of the process is challenging as there are two unknown evolving interfaces, i.e. the fluid-fluid interface and the depositing front. Both interfaces are captured via the level-set method. The deposition at the depositing front is modeled as a first order reaction. The two immiscible fluids are modeled using the incompressible Navier-Stokes equations. Solution of the equations is implemented using a finite volume method. The model is then verified against known solutions. Preliminary results on deposition process in a two-fluid flow environment are presented. [Preview Abstract] |
Tuesday, November 25, 2014 3:28PM - 3:41PM |
R28.00012: Modeling of hydrodynamic forces on a finite-sized spherical particle due to a planar shock wave Subramanian Annamalai, Manoj Parmar, Yash Mehta, S. Balachandar Shock-particle interaction is a very important phenomenon, for example in the study of explosive dispersal of particles. When conducting simulations involving millions of particles, it is not feasible to resolve the flow around each particle. Therefore the goal here is to obtain an exact analytic solution for shock-particle interaction in the limit of weak shock, and based on which propose a model which can estimate the force on a particle as a finite-strength shock wave passes over it. For the exact solution we consider an acoustic wave passing over a finite-sized rigid spherical particle situated in a viscous compressible ambient fluid. Linearized Navier-Stokes equations are solved to evaluate the (first-order) force that acts upon the particle due to this disturbance (acoustic wave). In the inviscid limit we observe that our force expression is identical to that obtained by Parmar et al., J. Fluid Mech. 699, 352 (2012), although the latter's work was limited to only small particle diameters. However we clearly see the viscous forces to depend on particle size. The overall force thus obtained is compared against DNS results. Our model is able to correctly predict the magnitude of the peak force in addition to the time at which the maximum occurs. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700