Gravity Currents in the Laboratory, Atmosphere, and Ocean

Simpson, John

doi:10.1146/annurev.fl.14.010182.001241

Cited by 433 publications

(258 citation statements)

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“…We consider α k first and note that it assumes different values for the horizontal and inclined cases but has the same value for widening channels and squeezing fractures with the same inclination. The critical value α k depends on n and b and reduces to that predicted by Longo et al [37] for a constant cross section (b = 0); further considering a Newtonian fluid (n = 1) yields 1 2 for horizontal and 1 for inclined channels [32]. Furthermore, α k is defined only below a critical value b k of b, listed in tables 1 and 2 as well; b k depends only on the channel/fracture inclination but again assumes the same value for widening channels and squeezing fractures.…”

Section: Discussion Of Resultsmentioning

confidence: 56%

“…Propagation of viscous gravity currents inside confining boundaries: the effects of fluid rheology and channel geometry S. Longo 1 A theoretical and experimental investigation of the propagation of free-surface, channelized viscous gravity currents is conducted to examine the combined effects of fluid rheology, boundary geometry and channel inclination. The fluid is characterized by a power-law constitutive equation with behaviour index n. The channel cross section is limited by a rigid boundary of height parametrized by k and has a longitudinal variation described by the constant b ≥ 0.…”

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Propagation of viscous gravity currents inside confining boundaries: the effects of fluid rheology and channel geometry

2015

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Section: Discussion Of Resultsmentioning

confidence: 56%

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confidence: 99%

Propagation of viscous gravity currents inside confining boundaries: the effects of fluid rheology and channel geometry

2015

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“…Pyroclastic flows are now recognised as a class of gravity current (Wilson, 1980;Simpson, 1982). A number of the geological features of their deposits and the behaviour of the flows themselves indicate that mixing of air into the flow head is important.…”

Section: Introductionmentioning

confidence: 99%

A laboratory simulation of pyroclastic flows down slopes

Huppert

Turner

Carey

et al. 1986

Journal of Volcanology and Geothermal Research

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Huppert, H.E., Turner, J.S., Carey, S.N., Sparks, R.S.J. and Hallworth, M.A. 19~6. A laboratory simulation of pyroclastic flows down slopes. J. Volcanol. Geotherm. Res., Laboratory experiments are described which explore the dynamical consequences of buoyant convective upflow observed above hot pyroclastic flows. In nature, the convection is produced by the hot ash particles exchanging heat with air mixed into the front and top of the pyroclastic flow. This effect on the buoyancy due to the mixing of air and ash has been modelled in the laboratory using mixtures of methanol and ethylene glycol (MEG), which have a nonlinear density behaviour when mixed with water. Intermediate mixtures of these fluids can be denser than either initial component, and so the laboratory experiments were inverted models of the natural situation. We studied MEG flowing up under a sloping roof in a tank filled with water. The experiments were performed both in a narrow channel and on a laterally unconfined slope. The flow patterns were also compared with those of conventional gravity currents formed using fresh and salt water. The presence of the region of reversed buoyancy outside the layer flowing along the slope had two significant effects. First, it periodically protected the flow from direct mixing with the environment, resulting in pulses of relatively undiluted fluid moving out intermittently ahead of the main flow. Second, it produced a lateral inflow towards the axis of the current which kept the current confined to a narrow tongue, even on a wide slope.In pyroclastic flows the basal avalanche portion has a much larger density contrast with its surroundings than the laboratory flows. Calculations show that mixing of air into the dense part of a pyroclastic flow cannot generate a mixture that is buoyant in the atmosphere. However, the overlying dilute ash cloud can behave as a gravity current comparable in density contrast to the laboratory flows and can become buoyant, depending on the temperature and ash content. In the August 7th pyroclastic flow of Mount St. Helens, Hoblitt (1986) describes pulsations in the flow front, which are reminiscent of those observed in the experiments. As proposed by Hoblitt, the pulsations are caused by the ash cloud accelerating away from the front of the dense avalanche as a density 0377-0273/86/$03.50

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“…The total buoyancy in the gravitycurrent head may increase if the velocity on the floor is sufficiently high to cause resuspension of the particulate matter from the floor. The advancement of the particulates toward the front and their re-entrainment into the wake is a mechanism responsible for the transport of fine sediments over long distances on the ocean floor [24]. The thickness of the boundary layer can play a critical role in the advance of the gravity-current head.…”

Section: Introductionmentioning

confidence: 99%

A two-dimensional inviscid model of the gravity-current head by Lagrangian block simulation

Chu

Altai

2017

Environ Fluid Mech

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A two-dimensional inviscid model of the gravity-current head produced by the release of a relatively small volume of dense fluid from behind a tall lock gate is constructed by Lagrangian block simulation. Three numerical experiments are conducted for the lock's height-to-length aspect ratios H/L o = 8, 4 and 2. The front speeds obtained by the simulations agree with the laboratory observation for a similar range of aspect ratios. The floor velocity in the wake behind these heads is found to be greater than their front speed. The high floor velocity is caused by the impingement of the coherent wake vortex on the floor. It is a condition that permits these gravity-current heads to maintain their structural integrity so that the fine sediments can travel with the head over long distances on the ocean floor. The structural coherence of the current head depends on the lock aspect ratio. The gravity-current head produced by the release from the lock with the highest aspect ratio of H/L o = 8 is most coherent and relatively has the greatest floor velocity and the least trailing current behind the head.Keywords Gravity-current head Á Coherent wake vortex Á 2D inviscid model Á Lagrangian block advection Á Streamfunction and vorticity formulation

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Gravity Currents in the Laboratory, Atmosphere, and Ocean

Cited by 433 publications

References 0 publications

Propagation of viscous gravity currents inside confining boundaries: the effects of fluid rheology and channel geometry

Propagation of viscous gravity currents inside confining boundaries: the effects of fluid rheology and channel geometry

A laboratory simulation of pyroclastic flows down slopes

A two-dimensional inviscid model of the gravity-current head by Lagrangian block simulation

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