Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session G37: Particle-Turbulence Interaction I |
Hide Abstracts |
Chair: Rui Ni, Johns Hopkins University Room: Georgia World Congress Center B409 |
Monday, November 19, 2018 10:35AM - 10:48AM |
G37.00001: The role of particle-turbulence interactions on fluid and thermal transport Jesse Capecelatro Strong coupling between particles and turbulence gives rise to a variety of complex flow regimes, from dense clusters to nearly-particle-free voids. Such coupling can effectively 'demix' the underlying flow. In this presentation, results from highly-resolved Eulerian-Lagrangian simulations are reported to understand the extent to which local flow heterogeneity augment or restrict turbulent kinetic energy (TKE) and average rates of heat transfer. Simulations of homogeneous sedimenting gas-solid flows and particle-laden channel flows are analyzed for a range of volume fractions and Prandtl numbers. It is found that varying flow regimes have substantial and non-trivial effects on the budget of TKE. We also find that clusters have a profound effect on the overall heat transfer efficiency. Simulations reveal that the gas phase is cooled relatively fast in the vicinity of clusters while hot spots persist in regions void of particles. To identify the mechanisms responsible for these variations, a coarse grained temperature equation is derived for statistically homogeneous (zero-dimensional) time-dependent multiphase flows. Two-phase flow statistics are presented and a simplified model is proposed. |
Monday, November 19, 2018 10:48AM - 11:01AM |
G37.00002: Transport and Clustering of Inertial Particles in a Turbulent Channel Flow Kee Onn Fong, Omid Amili, Filippo Coletti Small inertial particles in wall-bounded turbulent flows are ubiquitous in natural and industrial settings, and exhibit a rich spectrum of behaviors depending on the flow regime and on the distance from the wall. We present experimental observations of the velocity response and topological distribution of dispersed, inertial particles in the turbulent downward flow through a vertical channel. The working fluid is air laden with size-selected glass spheres, which are imaged over wall-normal and wall-parallel windows and analyzed by particle tracking velocimetry. The particle spatial distribution is analyzed by radial distribution functions and Voronoi tessellation. The wall-normal profiles are strongly modified at higher (although still dilute) mass loading, indicating the particles modify the underlying turbulent flow. The particles accumulate near the wall by turbophoresis and form low-speed streaks, while the channel core is characterized by fractal-like clusters, also preferentially aligned in streamwise direction but travelling faster than the fluid. Spatial velocity correlations of the particle velocity fields allows to quantify the contribution from random uncorrelated motions. The findings are discussed in the context of modeling strategies for dispersed multiphase flows. |
Monday, November 19, 2018 11:01AM - 11:14AM |
G37.00003: The effect of particle inertia on particle-induced Rayleigh Taylor instabilities Sara Nasab, Pascale Garaud We present Direct Numerical Simulations to investigate the role particle inertia has on Rayleigh-Taylor instabilities on particle-laden flows. We consider dilute systems in which small, inertial particles are coupled to the fluid through drag. We use the two-fluid model, in which we solve for the fluid and particle motion separately. In our simulations, for a given overall density profile, we found that there are three possible outcomes: (1) For very small particles where inertia is negligible, the particle field becomes fully mixed and the instability shuts itself off. (2) For intermediate-sized particles where inertia is significant, turbulent-induced concentration can drive and maintain convection perpetually. (3) For very large particles, the rapid settling velocity prevents the development of the instability. We explore these three dynamical regimes and discuss potential applications. |
Monday, November 19, 2018 11:14AM - 11:27AM |
G37.00004: The effect of background air turbulence on liquid spray Douglas Carter, Filippo Coletti The properties and behavior of spray droplets are crucially affected by background turbulence. While this has far-reaching consequences e.g. in combustion systems, the effect of background turbulence on liquid spray has not been systematically studied and is not well understood. We experimentally investigate the properties of a liquid spray produced by a hollow-cone nozzle and injected into a large air chamber. The latter contains two planar arrays of individually actuated jets that can be fired in randomized sequence to produce a large region of homogeneous turbulence. We characterize the properties of the spray issued in quiescent and turbulent air, and in particular: the spray penetration, its mixing with the surrounding air, and the droplet size distribution. To this end, we perform planar imaging over a range of spatial and temporal resolutions. Focusing on a window in the far field, we perform particle tracking velocimetry using a high-speed laser and camera system, and droplet sizing by shadowgraphy using a high-resolution camera mounted on a long-range microscope and synchronized with a pulsed LED. We characterize droplet size, local concentration, and velocity, gaining insight on the spray dynamics and its interaction with turbulence. |
Monday, November 19, 2018 11:27AM - 11:40AM |
G37.00005: Vertical dispersion of inertial particles in wall-bounded turbulence David H Richter, Guiquan Wang, Marcelo Chamecki The turbulent transport of scalars in wall-bounded turbulence is an important problem that has received a great deal of attention. Similarity theory suggests that the scalar concentration exhibits a logarithmic wall-normal profile, which implies that vertical scalar fluxes are uniform with height. An extension of this theory, begun by Rouse and Prandtl, includes when the particles are heavy, i.e. they experience gravitational settling towards the wall. In this scenario the upwards turbulent flux can come into balance with the downwards settling velocity, and what results is a concentration profile which obeys a power law with wall-normal distance whose exponent is often referred to as the Rouse number. In this study, we extend this problem to include the effects of particle inertia, and consider whether or not this similarity theory holds for particles which are not necessarily traveling with the local fluid velocity. Direct numerical simulation with Lagrangian point particles are used to test asymptotic extensions to the Prandtl/Rouse theory, and interpretations are offered on how to describe the flux-profile relationship of settling, inertial particles in wall-bounded turbulence. |
Monday, November 19, 2018 11:40AM - 11:53AM |
G37.00006: Interfacial mass transfer in a turbulent multiphase flow Ashwanth Salibindla, Shiyong Tan, Ashik Masuk, Rui Ni In many applications, such as rain droplets in clouds, vapor bubbles in sub-cooled environments, heat and mass transfer between the two phases occurs via dissolution, evaporation, and chemical reactions. For the simplest case, mass diffused out of large inertial particles will be transported and mixed by the surrounding turbulence. One important aspect of this problem is the flow structures of turbulence, so-called Lagrangian coherent structures (LCS) that serve as the transport barrier. Therefore, we designed an experimental system to simultaneously obtain the Lagrangian coherent structures as well as the dynamics of inertial particles that continuously release mass to be mixed in the surrounding flow. This experiment will help us to unveil how the interfacial mass transfer is coupled with the turbulent transport and how this coupling is affected by the flow structure. |
Monday, November 19, 2018 11:53AM - 12:06PM |
G37.00007: Vertical particle-laden jet flow with a horizontal crossflow Jooyeon Park, Hyungmin Park It is well known that a cluster of particles (Stokes number around 1.0) exhibits the maximum concentration at the positions of higher strain rate (lower vorticity), so-called preferential concentration. While this has been studied mostly on small scale (turbulence scale), particle dispersions in a larger-scale motion have not been investigated widely. We experimentally study vertical particle-laden jet flows with a crossflow while varying the velocity ratio between jet and crossflow, and particle Stokes number (0.03-10.7). For each case, the single-phase flow is measured with a particle image velocimetry and then particle (Silicon, 10-75 um in size) distributions are measured separately, which is further quantified using Voronoi diagram analysis and planar nephelometry. Similar to previous studies, it is also measured that the maximum preferential concentration occurs when the Stokes number is near 1.0. Without a crossflow, the particles tend to accumulated on the center plane (dispersed mainly along the jet direction). However, with a crossflow, the particles move to the jet shear plane and are clustered around the particle source (i.e., jet exit). More discussions on the particle dispersion will be provided. |
Monday, November 19, 2018 12:06PM - 12:19PM |
G37.00008: Investigation of sphere dynamics within a turbulent boundary layer Yi Hui Tee, Diogo Barros, Ellen K. Longmire A spherical particle in a turbulent boundary layer undergoes complicated particle-wall and particle-turbulence interactions. Wall friction will affect the particle rolling and sliding motions while coherent flow structures can lift the particle away from the wall. To resolve the sphere dynamics in this flow, a 3D particle tracking experiment is conducted in a water channel facility. A sphere marked with dots on its surface is released from rest on a smooth wall and allowed to propagate with the flow at Re_{τ} = 700 and 1300. Spheres with diameter of 60 and 120 wall units and specific gravity of 1.003, 1.05 and 1.15 are used to understand turbulence, wall and gravity effects. Two pairs of high-speed cameras are arranged in stereo configurations to track the sphere translation and rotation. At both Re_{τ}, once released, the lightest sphere always lifts off from the wall and reaches an initial peak height before descending. The sphere can either collide with the wall and saltate or remain suspended at various heights. Meanwhile, the densest sphere does not lift off, but slides and can saltate along the wall. In all cases, the sphere can rotate about all three coordinate axes. Quantitative data on both translational and rotational behaviors will be presented. |
Monday, November 19, 2018 12:19PM - 12:32PM |
G37.00009: Electrically induced suppression of turbophoresis in particle-laden wall-bounded turbulent flows Mario Di Renzo, Maxime Bassenne, Perry L Johnson, Laura Villafane, Javier Urzay Turbophoresis is a ponderomotive effect whereby small inertial particles tend to drift toward the wall in wall-bounded turbulent flows. In this study, direct numerical simulations of incompressible turbulent channel flows laden with monodisperse small inertial particles are employed that illustrate the suppression of turbophoresis using external electric fields. An Eulerian/Lagrangian formulation is employed along with a fast multipole method for the electric potential conveniently corrected with boundary conditions. Characteristic regimes in the space of dimensionless parameters are identified where an AC electric field applied across the channel walls is capable of decreasing the time-averaged concentration of particles near the wall by two orders of magnitude. |
Monday, November 19, 2018 12:32PM - 12:45PM |
G37.00010: Turbulent flow of dense suspensions over viscous hyper-elastic walls Luca Brandt, Mehdi Niazi Ardekani The turbulent flow of suspensions of finite-size rigid spherical particles in channels with deformable walls is investigated. We perform direct numerical simulations with different wall elasticities at a fixed bulk Reynolds number of 5600 and compare the results against the particulate cases with a solid volume fraction of 10%. The flow is governed by the incompressible Navier– Stokes equations whereas the walls are modelled as a neo-Hookean material, satisfying the incompressible Mooney–Rivlin equation. A direct-forcing immersed boundary method is used to account for the particle-fluid interactions, combined with a collision model and lubrication corrections for short-range particle-particle and particle-wall interactions. Our results indicate a non-monotonic behavior of the skin friction and turbulence activity when increasing the material elastic modulus. Comparing with the single-phase flow for the same wall elasticity, drag reduction is observed in the particulate cases for the highly elastic walls in contrast to the less deformable walls where particles induce drag increase. Detailed statistics of the fluid and particle phase will be presented at the conference. |
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. |
© 2023 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
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700