Gravity currents over fixed beds of monodisperse spheres

Köllner, Thomas; Meredith, Alex; Nokes, Roger; Meiburg, Eckart

doi:10.1017/jfm.2020.550

Cited by 9 publications

(5 citation statements)

References 49 publications

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“…In relation to the above discussion, it is interesting to consider the possible scenarios in which an ‘exchange’ flow (i.e. when horizontal velocities become negative within the gravity current) may occur [35]. As shown by the streamlines in figure 2 (and confirmed by numerical simulations), the flows we have so far studied exclusively have fluid draining from region I into region II.…”

Section: Discussionmentioning

confidence: 99%

Anisotropy distorts the spreading of a fixed volume porous gravity current

Benham

2023

Proc. R. Soc. A.

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We consider the release and subsequent gravity-driven spreading of a dense finite volume of fluid in an anisotropic porous medium bounded by an impermeable substrate. When the permeability in the vertical direction is much smaller than in the horizontal direction, as is the case in many real geological reservoirs, this restricts the spread of the current to a very thin layer near the impermeable base. Using a combination of asymptotic analysis and finite difference computations of Darcy flow, we show that there exist two distinct flow regimes. At early times, the bulk of the current descends slowly and uniformly, injecting fluid into thin finger-like regions near the base. At much later times, the current transitions to the classical gravity-driven solution and continues to spread with a self-similar shape. One interesting consequence is that the swept volume of the current grows differently depending on the anisotropy of the medium. This has important consequences for managing contaminant spills, where it is important to minimize the contacted volume of the aquifer, or during geological CO 2 sequestration where a larger contacted volume results in more CO 2 being stored.

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Section: Discussionmentioning

confidence: 99%

Anisotropy distorts the spreading of a fixed volume porous gravity current

Benham

2023

Proc. R. Soc. A.

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“…Periodic fluctuations are present in the Froude numbers shown in panels c and d due to the seiche waves that are inevitably produced by the removal of the lock gate [24]. Prior to the roughness ( t < 0), all currents behave as canonical smooth-bed currents with a Froude number of approximately 0.46 as shown by the dashed line on Figs.…”

Section: Current Velocitymentioning

confidence: 94%

“…PTV results are not used in a quantitative way within this paper so are only briefly described here. However, the measurement system is fully described within Köllner et al [24] for related experiments. Several experiments were repeated multiple times to assess the repeatability of the measurements.…”

Section: Boundarymentioning

confidence: 99%

“…Wilson et al [23] observed the increased entrainment and subsequent re-establishment of a current interacting with a rectangular obstacle. Köllner et al [24] employed experiments and DNS to study a gravity current travelling over monodisperse, closely-packed spheres. It was found that the speed and density of the head reduce with time but that, in contrast to an array of cylinders, the closely packed matrix of the bed slows the rate of dilution into the head.…”

Section: Introductionmentioning

confidence: 99%

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The transient behaviour of through-flowing gravity currents interacting with a roughness array

Meredith¹,

McConnochie²,

Nokes³

et al. 2022

Preprint

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We present laboratory experiments that investigate the structure and flow characteristics of gravity currents travelling through an array of roughness elements. The roughness elements are of comparable height to the gravity current such that the current flows through the roughness array rather than over it. The frontal velocity and density structure are measured as the current transitions from flowing along a smooth bed to flowing through the roughness array, and then back to a smooth bed. We find that, upon entering the roughness array, the gravity current decelerates and the density structure changes from the head and tail structure typical of smooth bed gravity currents, to a wedge shape. A model is presented that explains the deceleration and change in shape based on a dynamic balance between a pressure gradient within the current tail and a drag force associated with individual roughness elements. This model accurately predicts the deceleration of the gravity current, supporting the proposed dynamic balance.

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“…In studying obstacles for mitigation of density-driven currents, the bulk of literature concerns the case of an isolated (single) roughness element or obstacle, for example [17][18][19][20]. There have also been limited investigations in respect to the effect of form roughness on these currents, including Negretti et al [21], Peters [22], Tanino et al [23], Tokyay [24], Chowdhury [25], Bhaganagar [26], Howlett et al [27], Nasrollahpour et al [28], and Köllner et al [29]. These works have been mostly focused on the frontal region of the density currents.…”

Section: Introductionmentioning

confidence: 99%

Velocity Structure of Density Currents Propagating over Rough Beds

Nasrollahpour

Jamal

Ismail

et al. 2021

Water

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In most practical cases, density-driven currents flow over surfaces that are not smooth; however, the effects of bottom roughness on these currents have not been fully understood yet. Hence, this study aims to examine the velocity structure of density currents while propagating over rough beds. To this end, alterations in the vertical velocity profiles within the body of these currents were investigated in the presence of different bottom roughness configurations. Initially, laboratory experiments were carried out for density currents flowing over a smooth surface to provide a baseline for comparison. Thereafter, seven bottom roughness configurations were tested, encompassing both dense and sparse bottom roughness. The bottom roughness consisted of repeated arrays of square cross-section beams covering the full channel width and perpendicular to the flow direction. The primary results indicate that the bottom roughness decelerated the currents and modified the shape of velocity profiles, particularly in the region close to the bed. Additionally, a critical spacing of the roughness elements was detected for which the currents demonstrated the lowest velocities. For the spacings above the critical value, increasing the distance between the roughness elements had little impact on controlling the velocity of these currents. Moreover, using dimensional analysis, equations were developed for estimating the mean velocities of the currents flowing over various configurations of the bottom roughness. The findings of this research could contribute towards better parameterization and improved knowledge of density currents flowing over rough beds. This can lead to a better prediction of the evolution of these currents in many practical cases as well as improved planning and design measures for the control of such currents.

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Gravity currents over fixed beds of monodisperse spheres

Abstract: Abstract

Cited by 9 publications

References 49 publications

Anisotropy distorts the spreading of a fixed volume porous gravity current

Anisotropy distorts the spreading of a fixed volume porous gravity current

The transient behaviour of through-flowing gravity currents interacting with a roughness array

Velocity Structure of Density Currents Propagating over Rough Beds

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