Analysis and direct numerical simulation of the flow at a gravity-current head. Part 2. The lobe-and-cleft instability

Härtel, Carlos; Carlsson, Fredrik; Thunblom, Mattias

doi:10.1017/s0022112000001270

Cited by 127 publications

(108 citation statements)

References 11 publications

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“…Despite the different model setup, the lobe-cleft instability was observed and the same conclusion has been drawn. In particular, a linear stability analysis is provided in section 4 of Hartel et al (2000a) to explain this phenomenon.…”

Section: Lobe-cleft Instabilitymentioning

confidence: 99%

Numerical simulations of shoaling internal solitary waves of elevation

Subich

Stastna

2016

Physics of Fluids

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We present high-resolution, two-and three-dimensional direct numerical simulations of laboratory-scale, fully nonlinear internal solitary waves of elevation shoaling onto and over a small-amplitude shelf. The three-dimensional, mapped coordinate, spectral collocation method used for the simulations allows for accurate modelling of both the shoaling waves and the bottom boundary layer. We focus on wave-induced instabilities during the shoaling and de-shoaling processes. The shoaling of the waves is characterized by the formation of a quasi-trapped core which undergoes a spatially growing stratified shear instability at its edge and a lobe-cleft instability in its nose. Both of these instabilities develop and three-dimensionalize concurrently, leading to strong bottom shear stress. During the deshoaling process, the core breaks up and ejects fluid that forms a vortex-rich region near the down-sloping portion of the shelf. The flow in this region is highly turbulent and the bottom shear stress is extremely strong. Experiments with a corrugated bottom boundary are also performed. Boundary layer separation is found inside each of the corrugations during the wave's shoaling process. Our analyses suggest that all of these wave-induced instabilities can lead to enhanced turbulence in the water column and increased shear stress on the bottom boundary. Through the generation and evolution of these instabilities, the shoaling and de-shoaling cycles of internal solitary waves of elevation are likely to provide systematic mechanisms for material mixing and sediment resuspension. These mechanisms have significant environmental implications on the near-coastal regions of the world's oceans.iii

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Section: Lobe-cleft Instabilitymentioning

confidence: 99%

Numerical simulations of shoaling internal solitary waves of elevation

Subich

Stastna

2016

Physics of Fluids

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“…The grid resolution for suspensiondriven and scalar-driven surges is the same as that used in Zgheib et al [29,30] for rectangular releases, where the adequacy of the grid for converged solution has been established. Also the grid resolution employed is consistent with the requirement that the grid spacing must be of the order of O (ReSc) −1 / 2 [2,15] . We use two values for the Reynolds number Re = 8430 and Re = 8950 for suspension-driven and scalar-driven gravity surges, respectively.…”

Section: Mathematical Formulationmentioning

confidence: 91%

Suspension-Driven gravity surges on horizontal surfaces: Effect of the initial shape

2017

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OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 17810 We present results from highly resolved direct numerical simulations of canonical (axisymmetric and planar) and non-canonical (rectangular) configurations of horizontal suspension-driven gravity surges. We show that the dynamics along the initial minor and major axis of a rectangular release are roughly similar to that of a planar and axisymmetric current, respectively. However, contrary to expectation, we observe under certain conditions the final extent of the deposit from finite releases to surpass that from an equivalent planar current. This is attributed to a converging flow of the particle-laden mixture toward the initial minor axis, a behaviour that was previously reported for scalar-driven currents on uniform slopes [31]. This flow is observed to be correlated with the travelling of a perturbation wave generated at the extremity of the longest side that reaches the front of the shortest side in a finite time. A semi-empirical explicit expression (based on established relations for planar and axisymmetric currents) is proposed to predict the extent of the deposit in the entire x -y plane. Finally, we observe that for the same initial volume of a suspension-driven gravity surge, a release of larger initial horizontal aspect-ratio is able to retain particles in suspension for longer periods of time.

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“…Because of their unequal propagation speeds, some of the relatively faster vortex tubes will catch up with slower tubes ahead and merge to form bigger rolled up vortices (see Fig. 3 at t = 4 and t = 6) Furthermore, as the current starts to decelerate, (and because of the no-slip boundary condition at the bottom surface) lobe and cleft structures [21,15] begin to emerge rendering the once smooth front more complex and three-dimensional. The speed of the current continuously develops along its circumference, and as a result, the lobe and cleft structures evolve by merging and splitting along the front.…”

Section: Three-dimensional Structuresmentioning

confidence: 99%

Direct numerical simulation of cylindrical particle-laden gravity currents

2015

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numerical simulation of cylindrical particle-laden gravity currents. Computers and Fluids, Elsevier, 2015, 123, pp.23-31. <10.1016/j.compfluid.2015 b s t r a c tWe present results from direct numerical simulations (DNS) of cylindrical particle-laden gravity currents. We consider the case of a full depth release with monodisperse particles at a dilute concentration where particle-particle interactions may be neglected. The disperse phase is treated as a continuum and a twofluid formulation is adopted. We present results from two simulations at Reynolds numbers of 3450 and 10,000. Our results are in good agreement with previously reported experiments and theoretical models. At early times in the simulations, we observe a set of rolled up vortices that advance at varying speeds. These Kelvin-Helmholtz (K-H) vortex tubes are generated at the surface and exhibit a counter-clockwise rotation. In addition to the K-H vortices, another set of clockwise rotating vortex tubes initiate at the bottom surface and play a major role in the near wall dynamics. These vortex structures have a strong influence on wall shear-stress and deposition pattern. Their relations are explored as well.

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Analysis and direct numerical simulation of the flow at a gravity-current head. Part 2. The lobe-and-cleft instability

Cited by 127 publications

References 11 publications

Numerical simulations of shoaling internal solitary waves of elevation

Numerical simulations of shoaling internal solitary waves of elevation

Suspension-Driven gravity surges on horizontal surfaces: Effect of the initial shape

Direct numerical simulation of cylindrical particle-laden gravity currents

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