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Particle based simulation of turbulent sediment transport processes

Event Type: 
Date and Time: 
Friday, December 11, 2015 - 16:00
Bldg 500 “Conference Room 501A”
Event Sponsor: 
Parviz Moin, Director of Center for Turbulence Research
Justin Finn, Research Associate, University of Liverpool (UK)

The transport of sediments due to turbulent wave, current, and tidal flows can have lasting social and environmental consequences. This makes the development of improved predictive capabilities for sediment motion an engineering priority, and motivates fundamental investigations of particle-particle and particle-turbulence interactions in coastal, fluvial, and estuarine boundary layers. In this talk, I will first present practical multiphase modeling guidelines for conducting such simulations within a DNS/LES framework by recasting the particle Reynolds and Stokes number scaling from [1] in terms of the Shields parameter (non-dimensional shear stress) and sediment Galileo number. The scaling results show that a LES point-particle approach is well suited to perform simulations of sub-aqueous quartz sands (specific density ≈ 2.5, size ≈ 0.1mm−2mm) over a broad range of range of Shields parameters. I will then discuss a model of this type that has been tailored specifically to capture the individual and collective dynamics of sand grains having natural size and shape variations. Its capability for simulating sand transport in wave driven, oscillatory boundary layer flows will be demonstrated for both the bed-form (dune, ripple) regime as well as the more energetic “sheet flow” regime, with detailed comparison made to the mobile-bed experimental measurements of [2] and [3]. Discussion of the results will focus on the intra-wave variation of the particle size distribution and the influence of three-dimensional vortical features on sand entrainment and suspension processes.

[1] S Balachandar. A scaling analysis for point–particle approaches to turbulent multiphase flows. International Journal of Multiphase Flow, 35(9):801–810, 2009.
[2] Tom O’Donoghue and Scott Wright. Flow tunnel measurements of velocities and sand flux in oscillatory sheet flow for well-sorted and graded sands. Coastal Engineering, 51(11):1163–1184, 2004.
[3] JJ Van der Werf, JS Doucette, T O’Donoghue, and JS Ribberink. Detailed measurements of velocities and suspended sand concentrations over full-scale ripples in irregular oscillatory flow. Journal of Geophysical Research, 112(F2):F02012, 2007.

Justin Finn received degrees in Mechanical Engineering from Oregon State University (PhD, Msc) and the University of Massachusetts (BSc). His graduate work involved simulation of flow in porous media, studies of bubble-vortex interactions, and coherent structure extraction from time dependent flows. He is currently appointed as a Research Associate in the Centre for Engineering Sustainability at the University of Liverpool (UK), where he develops computational tools to study Lagrangian transport behavior in geophysical and industrial systems.