Large-Eddy Simulations of Baroclinic Instability and Turbulent Mixing

2013 ◽  
Author(s):  
Eric D. Skyllingstad ◽  
Roger M. Samuelson
Keyword(s):  
Turbulent Mixing ◽  
Baroclinic Instability ◽  
Large Eddy Simulations ◽  
Large Eddy

A strategy for large-scale scalar advection in large eddy simulations that use the linear eddy sub-grid mixing model

2018 ◽  
Vol 28 (10) ◽  
pp. 2463-2479 ◽  
Author(s):  
Salman Arshad ◽  
Bo Kong ◽  
Alan Kerstein ◽  
Michael Oevermann
Keyword(s):  
Turbulent Mixing ◽  
Large Scale ◽  
Molecular Diffusion ◽  
Passive Scalar ◽  
Mixing Model ◽  
Large Eddy Simulations ◽  
High Flux ◽  
Scalar Mixing ◽  
Content Type ◽  
Large Eddy

PurposeThe purpose of this numerical work is to present and test a new approach for large-scale scalar advection (splicing) in large eddy simulations (LES) that use the linear eddy sub-grid mixing model (LEM) called the LES-LEM.Design/methodology/approachThe new splicing strategy is based on an ordered flux of spliced LEM segments. The principle is that low-flux segments have less momentum than high-flux segments and, therefore, are displaced less than high-flux segments. This strategy affects the order of both inflowing and outflowing LEM segments of an LES cell. The new splicing approach is implemented in a pressure-based fluid solver and tested by simulation of passive scalar transport in a co-flowing turbulent rectangular jet, instead of combustion simulation, to perform an isolated investigation of splicing. Comparison of the new splicing with a previous splicing approach is also done.FindingsThe simulation results show that the velocity statistics and passive scalar mixing are correctly predicted using the new splicing approach for the LES-LEM. It is argued that modeling of large-scale advection in the LES-LEM via splicing is reasonable, and the new splicing approach potentially captures the physics better than the old approach. The standard LES sub-grid mixing models do not represent turbulent mixing in a proper way because they do not adequately represent molecular diffusion processes and counter gradient effects. Scalar mixing in turbulent flow consists of two different processes, i.e. turbulent mixing that increases the interface between unmixed species and molecular diffusion. It is crucial to model these two processes individually at their respective time scales. The LEM explicitly includes both of these processes and has been used successfully as a sub-grid scalar mixing model (McMurtry et al., 1992; Sone and Menon, 2003). Here, the turbulent mixing capabilities of the LES-LEM with a modified splicing treatment are examined.Originality/valueThe splicing strategy proposed for the LES-LEM is original and has not been investigated before. Also, it is the first LES-LEM implementation using unstructured grids.

Large Eddy Simulations of scaled HTGR lower plenum for assessment of turbulent mixing

2018 ◽  
Vol 334 ◽  
pp. 24-41 ◽  
Author(s):  
Sasan Salkhordeh ◽  
Corey Clifford ◽  
Anirban Jana ◽  
Mark L. Kimber
Keyword(s):  
Turbulent Mixing ◽  
Large Eddy Simulations ◽  
Large Eddy

scholarly journals Accumulation and Subduction of Buoyant Material at Submesoscale Fronts

2018 ◽  
Vol 48 (6) ◽  
pp. 1233-1241 ◽  
Author(s):  
John R. Taylor
Keyword(s):  
Mixed Layer ◽  
Baroclinic Instability ◽  
Three Dimensional ◽  
Large Eddy Simulations ◽  
Surface Cooling ◽  
Additional Source ◽  
Tracer Concentration ◽  
Vertical Diffusivity ◽  
Large Eddy ◽  
Submesoscale Currents

AbstractThe influence of submesoscale currents on the distribution and subduction of passive, buoyant tracers in the mixed layer is examined using large-eddy simulations. Submesoscale eddies are generated through an ageostrophic baroclinic instability associated with a background horizontal buoyancy gradient. The simulations also include various levels of surface cooling, which provides an additional source of three-dimensional turbulence. Submesoscales compete against turbulent convection and restratify the mixed layer while generating strong turbulence along a submesoscale front. Buoyant tracers accumulate at the surface along the submesoscale front where they are subducted down into the water column. The presence of submesoscales strongly modifies the vertical tracer flux, even in the presence of strong convective forcing. The correlation between high tracer concentration and strong downwelling enhances the vertical diffusivity for buoyant tracers.

Hybrid Reynolds-Averaged Navier-Stokes/Large-Eddy Simulations of Supersonic Turbulent Mixing

AIAA Journal ◽  
2003 ◽  
Vol 41 (2) ◽  
pp. 218-229 ◽  
Author(s):  
Nicholas J. Georgiadis ◽  
J. Iwan D. Alexander ◽  
Eli Reshotko
Keyword(s):  
Turbulent Mixing ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes

Computational Studies of Two-Dimensional Rayleigh-Taylor Driven Mixing for a Tilted-Rig

2014 ◽  
Vol 136 (9) ◽  
Author(s):  
Malcolm J. Andrews ◽  
David L. Youngs ◽  
Daniel Livescu ◽  
Tie Wei
Keyword(s):  
Turbulent Mixing ◽  
Large Scale ◽  
Large Eddy Simulations ◽  
Two Dimensional ◽  
Complex Flows ◽  
Molecular Mixing ◽  
One Dimensional ◽  
Large Eddy ◽  
Mixing Problem ◽  
Good Agreement

A time-dependent, incompressible, turbulent mixing problem, referred here to as the “tilted-rig,” is defined, based results from an experiment that involved the introduction of a large-scale overturning motion, with a superposed localized Rayleigh-Taylor (RT) driven mixing. The problem serves to examine the development of RT turbulent mixing while being strained by a large-scale two-dimensional confined motion. Care is taken to define the problem in detail so others might use the definition, and the results, to help develop advanced models of buoyancy driven mixing in complex flows. Aside from a careful definition, the problem has been solved using two different implicit-large-Eddy-simulations (ILES) based codes, and with a direct numerical simulations (DNS) code. Two-dimensional and one-dimensional mix metrics are defined, and then used to examine the development of the mixing region, and the overall evolution of the flow. Comparison of simulations with experiment reveals that large-scale overturning can be well captured in all the simulations, similarly central mix widths, and spike/bubble sidewall penetrations are also in good agreement. A comparison between the different simulation methodologies, ILES and DNS, reveals an overall good agreement between mix metrics such as the amount of molecular mixing. The DNS simulations reveal a dependency on Reynolds number that merits further experimental work.

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