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 M36: Porous Media Flows I |
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Chair: Anthony Ladd, University of Florida Room: Georgia World Congress Center B408 |
Tuesday, November 20, 2018 8:00AM - 8:13AM |
M36.00001: Positron Emission Particle Tracking (PEPT) measurements of flow in porous media Arthur Ruggles, Cody Wiggins Positron Emission Particle Tracking (PEPT) is emerging as a measurement technique for flow in granular media and material processing equipment and is of interest to experimental fluid dynamics as it offers the potential for the study of flows in apparatuses lacking optical access. Here, PEPT is explored as a viable means of Lagrangian particle tracking for studies of diffusion in porous media. Packed beds are constructed of glass beads of varying sizes and particle tracking studies are conducted therein using water as the working fluid. Measured trajectories are then analyzed to validate various models of anomalous diffusion in porous systems. This work focuses on the deployment of PEPT for porous media study and preliminary results in packed bed systems. |
Tuesday, November 20, 2018 8:13AM - 8:26AM |
M36.00002: Hydrodynamic characteristics of flow in a stochastic foam Chanhee Moon, Kyung Chun Kim Random nature of stochastic foam provides favorable geometrical properties for thermal applications owing to large specific surface area and high porosity. However, notwithstanding intensive investigations for the last two decades, hydrodynamic characteristics of stochastic foam are still poorly understood. Current 3-D printing technology supports fabrication of transparent complex structures. This study investigates flow characteristics of a stochastic foam. Using micro-tomography and stereo-lithography, a transparent stochastic foam was printed. Quantitative flow visualization was performed using refractive index matching technique and particle image velocimetry. Mixing and drag characteristics were discussed. Mechanical mixing and fast free stream velocity of stochastic foam are beneficial for thermal applications, but large wake area behind the struts causes high pressure drop. On the basis of the results, a novel foam structure is suggested with lower form drag than the stochastic foam but with similar friction drag. |
Tuesday, November 20, 2018 8:26AM - 8:39AM |
M36.00003: Recognition of Permeability from Images with Convolutional Neural Networks Xiaolong Yin, Jinlong Wu, Heng Xiao In the study of porous media, image-based analysis immediately emerged as scanning high-resolution images of porous media became available. Pore-scale simulations often incur significant computational costs. The success of image recognition neural networks motivated us to seek fast prediction of porous media properties directly from images. Our steps to validate this concept included (1) generation of synthetic porous media samples, (2) computation of permeability via fluid dynamics simulations, (3) training of convolutional neural networks (CNN) with simulated data, and (4) validations against simulations. Comparison of machine learning predictions and the ground truths from simulations suggests excellent predictive performance across a wide range of porosities and pore geometries, especially for those with dilated pores whose permeability cannot be estimated using the conventional Kozeny-Carman approach. Incorporation of physical parameters (physics-informed CNN) improved the performance of the neural network. CNN-based methods are orders of magnitude faster than direct simulations using lattice Boltzmann. The proposed framework should be applicable to other physical properties of porous media as long as they are solely governed by pore geometry. |
Tuesday, November 20, 2018 8:39AM - 8:52AM |
M36.00004: Upscaling the Navier-Stokes Equation for Turbulent Flows in Porous Media Using the Method of Volume Averaging Xiaoliang He, Sourabh Apte, Brian Wood The closure problem for turbulent flows through packed beds has drawn much attention in the recent decade, because of the extensive applications in both natural and engineering systems. Different from the conventional method of directly modifying the Darcy-Forchheimer correlation, using RANS models or the double-averaging approach, the method of volume averaging (Whitaker 1996) is applied to develop the volume averaged Navier-Stokes equation (VANS). An algebraic model is proposed to close the VANS equation by upscaling the data obtained from direct numerical simulations (DNS). The DNS is performed in a face-centered cubic porous unit cell, where flows at different Reynolds numbers (10, 100, 200, 300, 500 and 1000) are simulated. The simple algebraic model is then assessed by comparing with a conventional, Forchheimer-correction-based model. The proposed model shows a better prediction of the macroscopic velocity especially at high Reynolds number flow regime. Finally, DNS of turbulent flows through a randomly packed porous bed is conducted to test the proposed model. |
Tuesday, November 20, 2018 8:52AM - 9:05AM |
M36.00005: Quantification of non-Newtonian fluids for flows in porous media in terms of energy dissipation rate: permeability, mobility and tortuosity Hye Kyeong Jang, Wook Ryol Hwang We propose a systematic approach in quantifying flows in a porous media with an alternative formulation of permeability, mobility and tortuosity using the energy dissipation rate . Two flow numbers (i.e., the coefficient of effective shear rate and the coefficient of energy dissipation rate), which depend nearly on the flow geometry, are adopted to quantify flow characteristics of porous flow system, independent of fluid rheology. First, the relationship of the permeability and the coefficient of energy dissipation rate will be discussed. Next, the mobility of inelastic non-Newtonian fluids (i.e., the relationship of Δp and Q ) for flows in porous media will be decomposed into the permeability and the effective viscosity, evaluated with the coefficient of effective shear rate and the coefficient of energy dissipation rate. Finally, we show that hydraulic tortuosity for quantifying sinuosity and interconnectedness of the pore space can also be expressed in terms of the two flow numbers as well as the porosity based on the energy dissipation rate. |
Tuesday, November 20, 2018 9:05AM - 9:18AM |
M36.00006: Flow field statistics and scaling in random 2D porous media Sadaf Sobhani, Sourabh Apte, Matthias Ihme Pore-scale simulations and analysis of fluid flow in a two-dimensional channel filled with a random array of cylinders are presented. Numerical calculations are obtained by solution of the Navier-Stokes equations using an unstructured finite-volume solver. The geometry of the random configurations are characterized by means of the Voronoi tessellation using cylinder center points. To investigate features such as large-scale coherence of the flow field, the Eulerian and Lagrangian statistics of the fluid velocity are computed and presented for a range of Reynolds numbers, spanning from the Darcy to the inertial and turbulent regimes. Additionally, the dependences of these statistics on the porosity and pore-length distributions of the random array of cylinders are presented, aiming to further the fundamental understanding of how the local pore structure controls large-scale flow features. These results have relevance in the characterization of properties such as tracer dispersion, pressure drop, and interphase convective heat transfer in porous media. |
Tuesday, November 20, 2018 9:18AM - 9:31AM |
M36.00007: Flow regimes through periodic arrays of cylinders Zahra Ibrahiam Khalifa, Liam Porcher, Kody Von Holdt, Raymond Karam, Nils G Tilton Steady single-phase flow through porous media is well understood in the low-Reynolds number regime for which the pore-scale flow is governed by Stokes' equations and the macroscopic flow satisfies the Darcy equation. At higher Reynolds numbers, however, questions remain about how to best model flows through porous media for which pore-scale inertial effects are important. This is particularly true when the pore-scale or macro-scale flow is also unsteady. Thus motivated, we perform a broad set of 2D direct numerical simulations of incompressible single phase flow through periodic arrays of cylinders using a finite volume method with immersed boundaries. We consider flows driven by either a steady pressure gradient or a gradient that oscillates in time. For steady pressure gradients, we systematically vary the porosity between 0.25 to 0.95, and the Reynolds number from the Stokes regime to regimes characterized by pore-scale unsteady vortex shedding. In this manner, we identify up to five regimes of steady macroscopic flow, each satisfying a different macroscopic relationship between the volume averaged pressure and velocity. These are then contrasted with cases driven by oscillating pressure gradients. For these cases, we focus on identifying critical Strouhal numbers. |
Tuesday, November 20, 2018 9:31AM - 9:44AM |
M36.00008: Instability analysis of the flow between two parallel plates where the bottom one coated with porous media Zhenxing Wu, Parisa Mirbod This study investigates the instability of pure Newtonian fluid flow between two parallel plates where the bottom one coated with various porous media with permeability, K and porosity, ε. We have applied normal modes to perturb the coupled flow system. Specifically, the effects of some dimensionless parameters such as depth ratio, permeability parameter, and the porosity of the porous medium on the instability have been examined. We found these parameters play a critical role in the instability. Depending on these parameters, instability is initiated and dominated either by the fluid or by the porous region. In particular, we found that there are ranges of the depth ratio and the permeability parameter for each value of the porous media porosity that affect the instability of this coupled flow. We have also determined a new parameter which specifies the potential dominance and the stability margin of each mode. To validate our calculations, we have also compared our results with the Orr-Sommerfeld equation. In addition, we have examined three special extreme conditions to study the coupled flow system in more detail. |
Tuesday, November 20, 2018 9:44AM - 9:57AM |
M36.00009: Non-Darcy flows of elastoviscoplastic fluids in porous media Francesco De Vita, Quinn Mitchell, Marco Edoardo Rosti, Luca Brandt, Sarah Hormozi We study flows of elastoviscoplastic fluids through porous media by numerical simulations. The porous media is made of cylinders arranged in a periodic fashion. We solve the Navier-Stokes equations combined with the elastoviscoplastic model proposed by Saramito for the stress tensor evolution. This study has two main contributions. First, we show that a nonlinear relationship exists between the pressure drop and the flow rate in the porous medium. This nonlinear relationship depends on plastic, elastic, inertial effects and the configuration of the porous field. Second, we study the details of flow as the limiting pressure gradient is approached, particularly showing how the limiting flows of yield stress fluids are affected by the elasticity of the fluid. |
Tuesday, November 20, 2018 9:57AM - 10:10AM |
M36.00010: Entraining porous media gravity currents Chunendra K. Sahu, Jerome Anthony Neufeld Porous media gravity currents are primarily horizontal flows driven by a density difference between fluids and limited by Darcy flow through the porous medium. They have been studied extensively both experimentally and theoretically under the assumption that the interface separating the two fluids is sharp. Here we present new experimental results performed using the dye-attenuation technique that quantify the amount of mixing within the spreading current. We find that the mixing may be significant even in homogeneous porous media, and particularly for heterogeneous media. This motivates our theoretical model, in which we assume that dispersive mixing between the ambient and injected fluid may be modelled using an entrainment hypothesis motivated by the well-known turbulent plume theory. Using this modified, porous media gravity current model we predict that for constant input flux the spreading and mixing of the current are self-similar and find good agreement between the experimental data and theoretical model. Moreover, we extend our entrainment model to examine the case of fixed volume, where a late-time cross-over from a dispersion to molecular diffusion limited regimes is possible. The behaviour of these regimes is confirmed using simplified numerical modelling. |
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