Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session A37: Particle-Laden Flows: Particle Resolved SimulationsParticles
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Chair: David Richter, Notre Dame Room: 303 |
Sunday, November 19, 2017 8:00AM - 8:13AM |
A37.00001: Importance of Variable Density and Non-Boussinesq Effects on the Drag of Spherical Particles Swetava Ganguli, Sanjiva Lele What are the forces that act on a particle as it moves in a fluid? How do they change in the presence of significant heat transfer from the particle, a variable density fluid or gravity? Last year, using particle-resolved simulations we quantified these effects on a single spherical particle and on particles in periodic lattices when O($10^{-3}$)~\textless~Re~\textless~O(10). Let $\lambda$ be the normalized particle-fluid temperature difference. Large deviations (\textgreater 50\%) in the absolute drag are observed as $\lambda$ approaches unity. Oppenheimer, et al (2016) [1] have proposed a theoretical formula for the drag of a heated sphere at extremely low Re. We show that when Re~\textgreater~O(10), inertial effects completely dominate the drag while when Re~\textless~O($10^{-3}$), viscous effects completely dominate the drag and our simulations agree well with [1]. In the middle, there is honest competition between inertial and viscous effects and the drag modification strongly depends on the thermally induced near-particle density variation causing a non-zero volumetric dilation rate. In the limit of $\lambda$ approaching 0 (Stokes' limit), the drag modification can also be captured as a correction to Stokes' drag using a suitable scaling based on the dilation rate. [Preview Abstract] |
Sunday, November 19, 2017 8:13AM - 8:26AM |
A37.00002: Fully resolved simulations of expansion waves propagating into particle beds Goran Marjanovic, Jason Hackl, Subramanian Annamalai, Thomas Jackson, S. Balachandar There is a tremendous amount of research that has been done on compression waves and shock waves moving over particles but very little concerning expansion waves. Using 3-D direct numerical simulations, this study will explore expansion waves propagating into fully resolved particle beds of varying volume fractions and geometric arrangements. The objectives of these simulations are as follows: 1) To fully resolve all (1-way coupled) forces on the particles in a time varying flow and 2) to verify state-of-the-art drag models for such complex flows. We will explore a range of volume fractions, from very low ones that are similar to single particle flows, to higher ones where nozzling effects are observed between neighboring particles. Further, we will explore two geometric arrangements: body centered cubic and face centered cubic. We will quantify the effects that volume fraction and geometric arrangement plays on the drag forces and flow fields experienced by the particles. These results will then be compared to theoretical predictions from a model based on the generalized Faxen's theorem. [Preview Abstract] |
Sunday, November 19, 2017 8:26AM - 8:39AM |
A37.00003: Numerical simulation of elasto-inertial particle migration in square channel flow of viscoelastic fluids Zhaosheng Yu In this paper, the inertia-elasticity-induced migration of a neutrally buoyant spherical particle in a pressure-driven square-shaped channel flow of an Oldroyd-B fluid is numerically investigated with a fictitious domain method. The particle lateral motion trajectories are shown for the bulk Reynolds number ranging from 1 to 100 and the Weissenberg number being up to 1.5.When the inertial effect is negligible, the particle migrates towards the channel centerline or the closest corner. As fluid elasticity is increased, the corner-attractive region is first extended and then shrinks, and the migration rate becomes larger. When the fluid inertial effect is not negligible, the particle migration equilibrium position depends strongly on the elasticity number and weakly on the Reynolds number. Our results reveal a new elasto-inertial equilibrium position located in the channel diagonal plane for the elasticity number in the range of 0.001 to 0.02. When the elasticity number exceeds around 0.02, the particle migrates towards the channel centerline or the closest corner. [Preview Abstract] |
Sunday, November 19, 2017 8:39AM - 8:52AM |
A37.00004: A Surface-Resolved DNS Study of Spherical Particles Settling In Quiescent Fluid Wyatt Horne, Krishnan Mahesh Surface-resolved numerical simulations using moving body-fitted grids are used to study the detailed fluid physics and body motion of spheres settling in quiescent fluid. A novel unstructured overset grid method is used which provides highly resolved near surface flow information that is used to connect the particle motion directly to detailed features in the fluid flow around the particle. Cases are presented over a range of Galileo numbers ($Ga$) at a fixed density ratio ($m^{*} {\approx} 8$). Included are Stokesian cases where the Maxey-Riley equations accurately predict the motion of the particle and cases where vorticity is shed from the particle’s surface into the quiescent fluid which results in non-trivial particle trajectories. Full particle trajectories are shown and compared to previous studies along with detailed flow information in the near and far wake. The hydrodynamic forcing on particles is analyzed and connected to features in the near and far wake within the quiescent fluid. [Preview Abstract] |
Sunday, November 19, 2017 8:52AM - 9:05AM |
A37.00005: Numerical study of heat and mass transfer in inertial suspensions in pipes. Mehdi Niazi Ardekani, Luca Brandt Controlling heat and mass transfer in particulate suspensions has many important applications such as packed and fluidized bed reactors and industrial dryers. In this work, we study the heat and mass transfer within a suspension of spherical particles in a laminar pipe flow, using the immersed boundary method (IBM) to account for the solid fluid interactions and a volume of fluid (VoF) method to resolve temperature equation both inside and outside of the particles. Tracers that follow the fluid streamlines are considered to investigate mass transfer within the suspension. Different particle volume fractions 5, 15, 30 and 40{\%} are simulated for different pipe to particle diameter ratios: 5, 10 and 15. The preliminary results quantify the heat and mass transfer enhancement with respect to a single-phase laminar pipe flow. We show in particular that the heat transfer from the wall saturates for volume fractions more than 30{\%}, however at high particle Reynolds numbers (small diameter ratios) the heat transfer continues to increase. Regarding the dispersion of tracer particles we show that the diffusivity of tracers increases with volume fraction in radial and stream-wise directions however it goes through a peak at 15{\%} in the azimuthal direction. [Preview Abstract] |
Sunday, November 19, 2017 9:05AM - 9:18AM |
A37.00006: Strong Shock Propagating Over A Random Bed of Spherical Particles Yash Mehta, Kambiz Salari, Thomas L. Jackson, S. Balachandar, Siddharth Thakur The study of shock interaction with particles has been largely motivated because of its wide-ranging applications. The complex interaction between the compressible flow features, such as shock wave and expansion fan, and the dispersed phase makes this multi-phase flow very difficult to predict and control. In this talk we will be presenting results on fully resolved inviscid simulations of shock interaction with random bed of particles. One of the fascinating observations from these simulations are the flow field fluctuations due to the presence of randomly distributed particles. Rigorous averaging (Favre averaging) of the governing equations results in Reynolds stress like term, which can be classified as pseudo turbulence in this case. We have computed this \textquotedblleft Reynolds stress\textquotedblright term along with individual fluctuations and the turbulent kinetic energy. Average pressure was also computed to characterize the strength of the transmitted and the reflected waves. [Preview Abstract] |
(Author Not Attending)
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A37.00007: Abstract Withdrawn
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Sunday, November 19, 2017 9:31AM - 9:44AM |
A37.00008: GPU acceleration of Eulerian-Lagrangian particle-laden turbulent flow simulations David Richter, James Sweet, Douglas Thain The Lagrangian point-particle approximation is a popular numerical technique for representing dispersed phases whose properties can substantially deviate from the local fluid. In many cases, particularly in the limit of one-way coupled systems, large numbers of particles are desired; this may be either because many physical particles are present (e.g. LES of an entire cloud), or because the use of many particles increases statistical convergence (e.g. high-order statistics). Solving the trajectories of very large numbers of particles can be problematic in traditional MPI implementations, however, and this study reports the benefits of using graphical processing units (GPUs) to integrate the particle equations of motion while preserving the original MPI version of the Eulerian flow solver. It is found that GPU acceleration becomes cost effective around one million particles, and performance enhancements of up to 15x can be achieved when $O(10^{8})$ particles are computed on the GPU rather than the CPU cluster. Optimizations and limitations will be discussed, as will prospects for expanding to two- and four-way coupled systems. [Preview Abstract] |
Sunday, November 19, 2017 9:44AM - 9:57AM |
A37.00009: Grain-resolving simulations of settling cohesive sediment Bernhard Vowinckel, Jade Whithers, Eckart Meiburg, Paolo Luzzatto-Fegiz Cohesive sediment is ubiquitous in natural environments such as rivers, lakes and coastal ecosystems. For this type of sediment, we can no longer ignore the short-range attractive forces that result in flocculation of aggregates much larger than the individual grain size. Hence, understanding the complex dynamics of the interplay between flocculated sediment and the ambient fluid is of prime interest for managing aquatic environments, although a comprehensive understanding of these phenomena is still lacking. In the present study, we address this issue by carrying out grain-resolved simulations of cohesive particles settling under gravity using the Immersed Boundary Method. We present a computational model formulation to accurately resolve the process of flocculation. The cohesive model is then applied to a complex test case. A randomly distributed ensemble of 1261 polydisperse particles is released in a tank of quiescent fluid. Subsequently, particles start to settle, thereby replacing fluid at the bottom of the tank, which induces a counter flow opposing the settling direction. This mechanism will be compared to experimental studies from the literature, as well as to the non-cohesive counterpart to assessthe impact of flocculation on sedimentation. [Preview Abstract] |
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