Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session S38: Porous Media Flow Mixing and Turbulence |
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Chair: Xiaoliang He, PNNL Room: 620 |
Tuesday, November 26, 2019 10:31AM - 10:44AM |
S38.00001: Pore-scale Direct Numerical Simulation of Turbulent Flows through a Randomly-Packed Porous Medium Xiaoliang He, Marshall Richmond, William Perkins, Timothy Scheibe, Sourabh Apte Turbulent flows through randomly-packed porous media are ubiquitous in both natural and engineered systems. It is of great value to understand the important turbulence characteristics in the randomly packed beds of relevance for heat transfer applications in chemical/nuclear reactors, as well as some environmental problems such as hyporheic exchange at the interface between free stream water and the underlying sediment. Currently, very few pore-scale direct numerical simulations (DNS) of high Reynolds number flows through packed beds have been conducted and almost all of these studies focused on structurally packed or dilute systems. In the present work, DNS are performed in a randomly-packed triply-periodic porous medium with a porosity of 0.37. The Eulerian and Lagrangian statistics of turbulence, TKE budget, anisotropy distribution in confined pore geometries are investigated. These observations are compared with our previous work on triple-periodic, face centered cubic (FCC), to understand the influence of the heterogeneity on the turbulent statistics. It is observed that the integral length scale in the random packing is larger than that from structured packing. [Preview Abstract] |
Tuesday, November 26, 2019 10:44AM - 10:57AM |
S38.00002: Transition to turbulence in randomly packed porous media: scale evolution of vortical structures Reza M. Ziazi, James Liburdy Vortical structures are the driving mechanism behind the process of transition to turbulence in randomly structured porous media that is observed in many natural processes; natural canopy forest fires and biological systems such as cardiovascular and respiratory. The investigation of vortex evolution during the onset of turbulence is performed by using time-resolved PIV to identify the flow structures, and measure the scale and energy of swirling structures as related to pore- and macro-scale Reynolds numbers. Objective local region-type ($\lambda_{\mathrm{ci}})$ versus non-local ($\Gamma_{\mathrm{2}})$ vortex identification methods are employed to detect the asymptotic scales at larger Re during transition from 100 to 1000. The direct measure of the size, strength, and number density of vortical structures are observed to show a similar trend and asymptote to turbulent scales at higher pore-scale Reynolds numbers. The shear and rotational contribution of vortical structures are influenced differently from pore- versus macro-scale Reynolds numbers which interprets the scale evolution during transition process. [Preview Abstract] |
Tuesday, November 26, 2019 10:57AM - 11:10AM |
S38.00003: Dispersion and stretching in 3D Porous media bloen metzger, mathieu souzy, yves meheust, tanguy le borgne, henri Lhuissier Mixing processes in complex flows are governed by the dispersion and stretching induced by the flow in question. However, even for the apparently simple case of a viscous flow through an isotropic porous medium, the statistics of these crucial kinematics quantities remain uncertain. We experimentally tackle this problem using an index-matched porous medium composed of randomly packed solid spheres. The 3D Eulerian velocity-field is characterized with an unprecedented resolution. The dispersion of advective particles is measured and explained in terms of the velocity statistics. Last, the stretching laws are measured for the first time using a Lagrangian stretching reconstruction method. These results provide solid grounds for a full description of mixing processes in porous media. [Preview Abstract] |
Tuesday, November 26, 2019 11:10AM - 11:23AM |
S38.00004: Geometric disorder regulates dispersion in viscoelastic porous media flows Derek M. Walkama, Nicolas Waisbord, Jeffrey S. Guasto In this work, we study the dispersion of microparticles in viscoelastic fluid flow through model, microfluidic porous media, comprising arrays of either hexagonally ordered or randomly disordered pillars. Similar to previous work at high Peclet number, we show that a viscoelastic flow instability in the ordered medium enhances dispersion transverse to the mean flow direction with increasing Weissenberg number (Wi). In contrast, we demonstrate that geometric disorder has two main consequences for transport: First, disorder quenches the elastic instability and thus, suppresses transverse dispersion due to a lack of chaotic velocity fluctuations. Second, we observe an enhancement of longitudinal dispersion, which corresponds with the emergence of channelized flow within the disordered medium. These filamentous flows strengthen in intensity with increasing Wi, where the origin of the increased longitudinal transport stems from their strongly-correlated streamwise flow speed. [Preview Abstract] |
Tuesday, November 26, 2019 11:23AM - 11:36AM |
S38.00005: Direct simulation of momentum transport across sediment-water interfaces with various particle roughness Guangchen Shen, Junlin Yuan, Mantha S. Phanikumar Vertical transport processes across the sediment-water interface play a significant role in biogeochemical processes in aquatic ecosystems. Most natural sediment beds are characterized by random shape, orientation, and arrangement of sediment grains. However, detailed understanding of the effects of bed-roughness characteristics isolated from those of permeability and bed forms is limited. Here, we use direct numerical simulation of a turbulent open-channel flow with a friction Reynolds number of 395 over a grain-resolved sediment bed, with a permeability Reynolds number of 2.6, a particle size of 70 in wall units, and two different configurations for the arrangement of sediment grains in the uppermost-layer: regular and random. The random interface results in a higher friction, higher penetration depths, more isotropic Reynolds stresses, and a more heterogeneous local-permeability distribution with a higher mean. It also leads to larger-scale and more intense time-mean pressure variations, which augments the form-induced vertical velocity magnitudes across the interface. The results demonstrate the mechanisms underlying the link between the bed-roughness details and the mass and momentum transports across the interface. [Preview Abstract] |
Tuesday, November 26, 2019 11:36AM - 11:49AM |
S38.00006: A generalised multi-rate model for conjugate transfer in heterogeneous media Federico Municchi, Matteo Icardi In fluid dynamics, conjugate heat/mass transfer refers to the problem of coupling a "mobile" fluid domain, where a flow field is established and thus advection-diffusion is the main transport mechanism, with "immobile" inclusions, where diffusion dominates. This is therefore relevant to a wide range of problems in subsurface flows, porous media, and heat transfer applications. Fully resolved simulations of this coupled process are often unfeasible due to the difficulties in capturing the possibly complicated, heterogeneous, and often uncertain micro-structures, and because of the wide range of spatio-temporal scales involved. Most of the times, studies at industrial or geological scale rely on appropriate upscaled models, where the conjugate transfer is not resolved directly, but is computed using a set of coupling parameters. In this talk, we present a novel generalised multi-rate model (GMRM) that provides a formal upscaling of the conjugate transfer problem in heterogeneous media where the coupling parameters can be computed from a cell problem. We also show that, unlike previous multi-rate models, the GMRM can be combined with standard homogenisation theory to account for non-uniform interface temperature distributions and non-equilibrium. [Preview Abstract] |
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