Small—Scale Statistics of the Passive Scalar Turbulent Mixing: A Test of the Influence of the Large—Scale Properties

1998 ◽  
pp. 557-560
Author(s):  
L. Danaila ◽  
F. Anselmet ◽  
P. Le Gal ◽  
C. Brun ◽  
A. Pumir ◽  
...  
Keyword(s):  
Turbulent Mixing ◽  
Large Scale ◽  
Passive Scalar ◽  
Small Scale ◽  
Scale Properties

scholarly journals Modeling the Ocean in Climate Studies

1984 ◽  
Vol 5 ◽  
pp. 133-140 ◽  
Author(s):  
Albert J. Semtner
Keyword(s):  
Turbulent Mixing ◽  
Large Scale ◽  
Deep Convection ◽  
Vertical Mixing ◽  
Mesoscale Eddies ◽  
Small Scale ◽  
Polar Regions ◽  
Sea Ice Extent ◽  
Modeling Strategy ◽  
Climate Studies

A number of processes in the ocean must be modeled properly in order to produce valid estimates of oceanic heat transport, sea-surface temperature, and sea-ice extent in climate studies. These include: wind-driven turbulent mixing and water transport in the surface layer, internal vertical mixing due to several small-scale mechanisms, horizontal and vertical exchanges by mesoscale eddies, mixing along isopycnals, large-scale transport by currents, deep convection in polar regions, and boundary exchanges with atmosphere, ice, and land. Techniques to model these processes are described. Prospects are given for parameterizing the effects of phenomena that cannot be resolved in climate studies, particularly mesoscale eddies. Past simulations of the ocean in climate studies are reviewed. A modeling strategy is outlined for an improved treatment of the ocean, consistent with the computational power soon to be available.

Predictions of Small-Scale Statistics for a Passive Scalar in Turbulent Mixing

1997 ◽  
Vol 79 (23) ◽  
pp. 4577-4580 ◽  
Author(s):  
L. Danaila ◽  
F. Anselmet ◽  
P. Le Gal ◽  
J. Dusek ◽  
C. Brun ◽  
...  
Keyword(s):  
Turbulent Mixing ◽  
Passive Scalar ◽  
Small Scale

scholarly journals Non-local dispersion and the reassessment of Richardson's t3-scaling law

2021 ◽  
Vol 932 ◽  
Author(s):  
G.E. Elsinga ◽  
T. Ishihara ◽  
J.C.R. Hunt
Keyword(s):  
Large Scale ◽  
Scaling Law ◽  
Taylor Dispersion ◽  
Small Time ◽  
Inertial Range ◽  
Small Scale ◽  
Mean Square ◽  
Dispersion Regime ◽  
Non Local ◽  
Scale Properties

The Richardson-scaling law states that the mean square separation of a fluid particle pair grows according to t3 within the inertial range and at intermediate times. The theories predicting this scaling regime assume that the pair separation is within the inertial range and that the dispersion is local, which means that only eddies at the scale of the separation contribute. These assumptions ignore the structural organization of the turbulent flow into large-scale shear layers, where the intense small-scale motions are bounded by the large-scale energetic motions. Therefore, the large scales contribute to the velocity difference across the small-scale structures. It is shown that, indeed, the pair dispersion inside these layers is highly non-local and approaches Taylor dispersion in a way that is fundamentally different from the Richardson-scaling law. Also, the layer's contribution to the overall mean square separation remains significant as the Reynolds number increases. This calls into question the validity of the theoretical assumptions. Moreover, a literature survey reveals that, so far, t3 scaling is not observed for initial separations within the inertial range. We propose that the intermediate pair dispersion regime is a transition region that connects the initial Batchelor- with the final Taylor-dispersion regime. Such a simple interpretation is shown to be consistent with observations and is able to explain why t3 scaling is found only for one specific initial separation outside the inertial range. Moreover, the model incorporates the observed non-local contribution to the dispersion, because it requires only small-time-scale properties and large-scale properties.

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.

scholarly journals The effect of coherent stirring on the advection–condensation of water vapour

2017 ◽  
Vol 473 (2202) ◽  
pp. 20170196 ◽  
Author(s):  
Yue-Kin Tsang ◽  
Jacques Vanneste
Keyword(s):  
Water Vapour ◽  
Large Scale ◽  
Passive Scalar ◽  
Hadley Cell ◽  
Moisture Distribution ◽  
Specific Humidity ◽  
Initial Time ◽  
Small Scale ◽  
Kinematic Models ◽  
Scale Turbulence

Atmospheric water vapour is an essential ingredient of weather and climate. The key features of its distribution can be represented by kinematic models which treat it as a passive scalar advected by a prescribed flow and reacting through condensation. Condensation acts as a sink that maintains specific humidity below a prescribed, space-dependent saturation value. To investigate how the interplay between large-scale advection, small-scale turbulence and condensation controls moisture distribution, we develop simple kinematic models which combine a single circulating flow with a Brownian-motion representation of turbulence. We first study the drying mechanism of a water-vapour anomaly released inside a vortex at an initial time. Next, we consider a cellular flow with a moisture source at a boundary. The statistically steady state attained shows features reminiscent of the Hadley cell such as boundary layers, a region of intense precipitation and a relative humidity minimum. Explicit results provide a detailed characterization of these features in the limit of strong flow.

scholarly journals A stochastic model for the polygonal tundra based on Poisson-Voronoi Diagrams

2012 ◽  
Vol 3 (1) ◽  
pp. 453-483
Author(s):  
F. Cresto Aleina ◽  
V. Brovkin ◽  
S. Muster ◽  
J. Boike ◽  
L. Kutzbach ◽  
...  
Keyword(s):  
Stochastic Model ◽  
Large Scale ◽  
Climate Models ◽  
Voronoi Diagrams ◽  
Field Studies ◽  
Statistical Characteristics ◽  
Small Scale ◽  
Landscape Response ◽  
Soil Heterogeneities ◽  
Scale Properties

Abstract. Sub-grid processes occur in various ecosystems and landscapes but, because of their small scale, they are not represented or poorly parameterized in climate models. These local heterogeneities are often important or even fundamental for energy and carbon balances. This is especially true for northern peatlands and in particular for the polygonal tundra where methane emissions are strongly influenced by spatial soil heterogeneities. We present a stochastic model for the surface topography of polygonal tundra using Poisson-Voronoi Diagrams and we compare the results with available recent field studies. We analyze seasonal dynamics of water table variations and the landscape response under different scenarios of precipitation income. We upscale methane fluxes by using a simple idealized model for methane emission. Hydraulic interconnectivities and large-scale drainage may also be investigated through percolation properties and thresholds in the Voronoi graph. The model captures the main statistical characteristics of the landscape topography, such as polygon area and surface properties as well as the water balance. This approach enables us to statistically relate large-scale properties of the system taking into account the main small-scale processes within the single polygons.

scholarly journals Large Landholdings in Brabant: Unravelling Urbanization Processes in the City-Territory

2020 ◽  
Vol 5 (2) ◽  
pp. 116-131
Author(s):  
Guillaume Vanneste
Keyword(s):  
Large Scale ◽  
18Th Century ◽  
Small Scale ◽  
Urban Transformations ◽  
The Subject ◽  
Scale Properties ◽  
Ecological Relations ◽  
The Village ◽  
The City ◽  
Fragmentation Processes

Through the observation of land property (le foncier) and, specifically, large landholdings, this research aims to take a fresh look at urbanization and urban planning in the Belgian Walloon Brabant Province. In contrast with most Belgian urban studies that tackle the issue of sprawling urbanization through small-scale parcels, fragmentation processes and individual initiatives, this investigation complements recent research on estate urbanization by examining large-scale properties and how they played a role in the city-territory’s urbanization during the second half of the 20th century. Large landholdings in Walloon Brabant are remnants of 18th century territorial dominions inherited from nobility and clergy, progressively dismantled, reorganized or maintained as result of the urbanization dynamics integral to the reproduction of modern and contemporary society. The village of Rixensart is the subject of a series of these transformations. By mapping the de Merode family’s large landholdings in the south of the commune and analyzing the allotments permit, we retrace urban transformations and the reordering of social and ecological relations through changing land structure. The palimpsest notion is used as a tool to unravel the set of actors involved in urbanization dynamics and to highlight the socio-spatial transformations and construction of recent urbanization. The profound transformations taking place in Walloon Brabant today present an opportunity to reflect on its future, and questions regarding landed estates suggest potential for tackling the city-territory’s greater systemic challenges.

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