Reynolds number and settling velocity influence for finite-release particle-laden gravity currents in a basin

Francisco, Ezequiel Pelisoli; Espath, Luis; Laizet, Sylvain; Silvestrini, Jorge Hugo

doi:10.1016/j.cageo.2017.09.010

Cited by 16 publications

(10 citation statements)

References 29 publications

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“…Future studies will be performed with a longer and deeper computational domain in order to better stabilize the plunge position. An open basin setup, more representative of real situations than a channelized setup, will also be considered following the recent work of Francisco et al () for finite‐release particle‐laden gravity currents. In most lakes and reservoirs, the variation of the inlet cross section is three‐dimensional, with both the depth and width increasing with distance so it is important to be able to reproduce this feature in future studies.…”

Section: Discussionmentioning

confidence: 99%

Three‐Dimensional Turbulence‐Resolving Simulations of the Plunge Phenomenon in a Tilted Channel

et al. 2018

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Hyperpycnal flows are produced when the density of a fluid flowing in a relatively quiescent basin is greater than the density of the fluid in the basin. The density differences can be due to the difference in temperatures, salinity, turbidity, concentration, or a combination of them. When the inflow momentum diminishes, the inflowing fluid eventually plunges under the basin fluid and flows along the bottom floor as an underflow density current. In the present work, 3-D turbulence-resolving simulations are performed for an hyperpycnal flow evolving at the bottom floor of a tilted channel. Using advanced numerical techniques designed for supercomputers, the incompressible Navier-Stokes and transport equations are solved to reproduce numerically the experiments of Lamb et al. (2010, https://doi.org/10.1130/B30125.1) obtained inside a flume with a long tilted ramp. This study focuses on presenting and validating a new numerical framework for the correct reproduction and analysis of the plunge phenomenon and its associated flow features. A very good agreement is found between the experimental data of Lamb et al. (2010), the analytical models of Parker and Toniolo (2007, https://doi.org/10.1061/(ASCE)0733-9429 (2007) 133:6(690)), and the present turbulence-resolving simulations. The mixing process between the ambient fluid and the underflow density current is also analyzed thanks to visualizations of vortical structures at the interface.

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Section: Discussionmentioning

confidence: 99%

Three‐Dimensional Turbulence‐Resolving Simulations of the Plunge Phenomenon in a Tilted Channel

et al. 2018

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“…These particles will never accelerate towards their undisturbed settling velocity, and as soon as there are more particles decelerating than accelerating, E k starts to decay. Hence, the evolution of E k reflects the behavior of a dissipative dynamical system released from rest, with an initial supply of potential energy, so that its dynamics resemble the temporal evolution of the fluid kinetic energy for a lock-release turbidity current propagating in a channel (Necker et al 2005) or spreading radially in a basin (Francisco et al 2018). The difference in settling velocities of the larger and smaller particles during the initial stage results in the strong stirring and mixing of both the fluid and the particles.…”

Section: Energetics Of Enhanced Settlingmentioning

confidence: 99%

Settling of cohesive sediment: particle-resolved simulations

et al. 2018

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We develop a physical and computational model for performing fully coupled, grainresolved Direct Numerical Simulations of cohesive sediment, based on the Immersed Boundary Method. The model distributes the cohesive forces over a thin shell surrounding each particle, thereby allowing for the spatial and temporal resolution of the cohesive forces during particle-particle interactions. The influence of the cohesive forces is captured by a single dimensionless parameter in the form of a cohesion number, which represents the ratio of cohesive and gravitational forces acting on a particle. We test and validate the cohesive force model for binary particle interactions in the Drafting-Kissing-Tumbling (DKT) configuration. Cohesive sediment grains can remain attached to each other during the tumbling phase following the initial collision, thereby giving rise to the formation of flocs. The DKT simulations demonstrate that cohesive particle pairs settle in a preferred orientation, with particles of very different sizes preferentially aligning themselves in the vertical direction, so that the smaller particle is drafted in the wake of the larger one. This preferred orientation of cohesive particle pairs is found to remain influential for systems of higher complexity. To this end, we perform large simulations of 1,261 polydisperse settling particles starting from rest. These simulations reproduce several earlier experimental observations by other authors, such as the accelerated settling of sand and silt particles due to particle bonding, the stratification of cohesive sediment deposits, and the consolidation process of the deposit. They identify three characteristic phases of the polydisperse settling process, viz. (i) initial stir-up phase with limited flocculation; (ii) enhanced settling phase characterized by increased flocculation; and (iii) consolidation phase. The simulations demonstrate that cohesive forces accelerate the overall settling process primarily because smaller grains attach to larger ones and settle in their wakes. For the present cohesion number values, we observe that settling can be accelerated by up to 29%. We propose physically based parametrization of classical hindered settling functions introduced by earlier authors, in order to account for cohesive forces. An investigation of the energy budget shows that, even though the work of the collision forces is much smaller than that of the hydrodynamic drag forces, it can substantially modify the relevant energy conversion processes.

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“…This so-called trace is assembled by applying static condensation to the degrees of freedom located inside the elements. Furthermore, for applications only involving simple geometries, FD methods with immersed boundary treatment on cartesian grids, as in the Incompact3D solver [48,49,50,51], are an attractive alternative to FE type methods. Their main advantage is that they allow an efficient Poisson solve via Fast Fourier Transforms.…”

Section: Incompressible Flowsmentioning

confidence: 99%

High-Order Incompressible Computational Fluid Dynamics on Modern Hardware Architectures

Loppi¹

2021

Preprint

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Modern GPU architectures are characterised by an abundance of compute capability relative to memory bandwidth. This makes them very well-suited to solving temporally explicit and spatially compact discretisations of hyperbolic conservation laws. However, classical pressure-projection-based incompressible Navier–Stokes formulations do not fall into this category. One attractive formulation for solving incompressible problems on modern hardware is the method of artificial compressibility. When combined with explicit dual time stepping and a high-order Flux Reconstruction discretisation, the majority of operations can be cast as arithmetically intensive matrix–matrix multiplications that are well-suited for GPUs. In this seminar, I will present the high-order cross-platform incompressible Navier–Stokes solver in PyFR, together with three explicit convergence acceleration techniques: a polynomial multigrid, a novel locally adaptive pseudo-time stepping approach and novel stability-optimised Runge-Kutta schemes. The solver and the convergence acceleration techniques are validated for a range of turbulent test cases, including a simulation of the DARPA SUBOFF submarine model using hundreds of NVIDIA GPUs.

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Reynolds number and settling velocity influence for finite-release particle-laden gravity currents in a basin

Cited by 16 publications

References 29 publications

Three‐Dimensional Turbulence‐Resolving Simulations of the Plunge Phenomenon in a Tilted Channel

Three‐Dimensional Turbulence‐Resolving Simulations of the Plunge Phenomenon in a Tilted Channel

Settling of cohesive sediment: particle-resolved simulations

High-Order Incompressible Computational Fluid Dynamics on Modern Hardware Architectures

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