Vortical Structure Characteristics of Transitional Flow Through Porous Media

Ziazi, Reza M.; Liburdy, James A.

doi:10.1115/ajkfluids2019-5094

Cited by 3 publications

(2 citation statements)

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“…These studies predict the following regimes: (i) steady laminar (29 < Re p < 193), (ii) unsteady laminar (46 < Re p < 156), (iii) steady inertial (1 < Re p < 148), (iv) unsteady inertial (148 < Re p < 300), (v) viscous-inertial transition (78 < Re p < 480), and (vi) turbulent (159 < Re p < 727). The deviations between these predictions are very wide 14,54,56,[60][61][62]90,91,93,94 Methods that have been applied include particle image velocimetry (PIV) 33,49,[68][69][70]96,[100][101][102][103][104] , particle tracking velocimetry (PTV) [105][106][107] , Laser Doppler Anemometry (LDA) 59,108 , Magnetic…”

Section: Introductionmentioning

confidence: 99%

Transition to turbulence in randomly packed porous media; scale estimation of vortical structures

Ziazi,

Liburdy

2020

Preprint

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Pore-scale observation of vortical flow structures in porous media is a significant challenge in many natural and industrial systems. Vortical structure dynamics is believed to be the driving mechanism in the transition regime in porous media based on the pore Reynolds number, Re p . To examine this assertion, a refractiveindex matched randomly packed porous medium with homogeneously-sized glass spheres (D B = 15mm) is designed to measure the scale of vortical flow structures in transition from unsteady laminar to turbulent using two-dimensional time-resolved particle image velocimetry. Planar Particle Image Velocimetry (PIV) data is used to quantify the scale of these structures with regard to size, strength, and number density using two different scalings (i) Re p macroscopic (global), and (ii) Re p microscopic (local, pore-scale). Data is obtained for Re p from 100 to 948 in six different locations from the center of the bed towards the wall (one bead diameter away from wall). Direct measurement of vortex scale is quantified by employing swirl strength (λ ci ), vortex core (Γ 2 ), and enhanced swirl strength (λ cr /λ ci ) vortex identification methods. These scales are compared with turbulent integral scales. Due to the confinement of the random medium, the inertia-dependent topology of the flow creates shear-dominant vortical structures in moderate unsteady laminar Reynolds numbers (Re p < 300), while the swirl-dominant flow structures appear in weak turbulent Reynolds numbers (Re p > 500). From the macroscopic point of view, (i) the size of vortical structures decreases asymptotically to reach 20% of the global hydraulic diameter, (ii) the strength of vortices increases monotonically by enhancing the inertial effects of Re p , and (iii) the average number density of vortical structures grows from unsteady laminar to fully turbulent. From the pore-scale (local) point of view using Re p , (i) the size of vortical structures decreases monotonically with increasing local Reynolds number, (ii) the strength of vortices rises with Re p , and (iii) the number density of vortical structures for different Re p is invariant relative to the pore size. These findings suggest pore versus macro-scale coupling exists for the scale of vortical flow structures in the transition regime, albeit the scale variation of pore-scale flow structures with local inertial effects is different from the asymptotic values captured in the macroscopic level with increasing Re p .

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Section: Introductionmentioning

confidence: 99%

Transition to turbulence in randomly packed porous media; scale estimation of vortical structures

Ziazi,

Liburdy

2020

Preprint

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“…The Reynolds numbers based on channels hydraulic diameter was 511, while the Reynolds number based on pore diameter was 100. These numbers prove that the flow regime was laminar; however, based on the Reynolds number of the pore diameter following recent publications [30][31][32], the flow regime was categorized as unsteady laminar, where the laminar wake oscillates. In addition, a bubble trap was installed to minimize the inflow of bubbles into the test section.…”

Section: Preliminary Experimentsmentioning

confidence: 63%

Time-Resolved PIV Measurements and Turbulence Characteristics of Flow Inside an Open-Cell Metal Foam

et al. 2021

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Open-cell metal foams are porous medium for thermo-fluidic systems. However, their complex geometry makes it difficult to perform time-resolved (TR) measurements inside them. In this study, a TR particle image velocimetry (PIV) method is introduced for use inside open-cell metal foam structures. Stereolithography 3D printing methods and conventional post-processing methods cannot be applied to metal foam structures; therefore, PolyJet 3D printing and post-processing methods were employed to fabricate a transparent metal foam replica. The key to obtaining acceptable transparency in this method is the complete removal of the support material from the printing surfaces. The flow characteristics inside a 10-pore-per-inch (PPI) metal foam were analyzed in which porosity is 0.92 while laminar flow condition is applied to inlet. The flow inside the foam replica is randomly divided and combined by the interconnected pore network. Robust crosswise motion occurs inside foam with approximately 23% bulk speed. Strong influence on transverse motion by metal foam is evident. In addition, span-wise vorticity evolution is similar to the integral time length scale of the stream-wise center plane. The span-wise vorticity fluctuation through the foam arrangement is presented. It is believed that this turbulent characteristic is caused by the interaction of jets that have different flow directions inside the metal foam structure. The finite-time Lyapunov exponent method is employed to visualize the vortex ridges. Fluctuating attracting and repelling material lines are expected to enhance the heat and mass transfer. The results presented in this study could be useful for understanding the flow characteristics inside metal foams.

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