scholarly journals Is spontaneous generation of coherent baroclinic flows possible?

2019 ◽  
Vol 862 ◽  
pp. 889-923 ◽  
Author(s):  
Nikolaos A. Bakas ◽  
Petros J. Ioannou
Keyword(s):  
Energy Input ◽  
Large Scale ◽  
Critical Threshold ◽  
Spontaneous Generation ◽  
Large Scale Structures ◽  
Zonal Jets ◽  
Statistical State ◽  
Coherent Vortices ◽  
Geophysical Turbulence ◽  
New Type

Geophysical turbulence is observed to self-organize into large-scale flows such as zonal jets and coherent vortices. Previous studies of barotropic $\unicode[STIX]{x1D6FD}$-plane turbulence have shown that coherent flows emerge from a background of homogeneous turbulence as a bifurcation when the turbulence intensity increases. The emergence of large-scale flows has been attributed to a new type of collective, symmetry-breaking instability of the statistical state dynamics of the turbulent flow. In this work, we extend the analysis to stratified flows and investigate turbulent self-organization in a two-layer fluid without any imposed mean north–south thermal gradient and with turbulence supported by an external random stirring. We use a second-order closure of the statistical state dynamics, that is termed S3T, with an appropriate averaging ansatz that allows the identification of statistical turbulent equilibria and their structural stability. The bifurcation of the statistically homogeneous equilibrium state to inhomogeneous equilibrium states comprising zonal jets and/or large-scale waves when the energy input rate of the excitation passes a critical threshold is analytically studied. Our theory predicts that there is a large bias towards the emergence of barotropic flows. If the scale of excitation is of the order of (or larger than) the deformation radius, the large-scale structures are barotropic. Mixed barotropic–baroclinic states with jets and/or waves arise when the excitation is at scales shorter than the deformation radius with the baroclinic component of the flow being subdominant for low energy input rates and insignificant for higher energy input rates. The predictions of the S3T theory are compared with nonlinear simulations. The theory is found to accurately predict both the critical transition parameters and the scales of the emergent structures but underestimates their amplitude.

On the generation of large-scale structures in a homogeneous eddy field

2010 ◽  
Vol 668 ◽  
pp. 76-99 ◽  
Author(s):  
TIMOUR RADKO
Keyword(s):  
Large Scale ◽  
Dissipative Systems ◽  
Spontaneous Generation ◽  
Asymptotic Model ◽  
Evolutionary Pattern ◽  
Long Wavelength ◽  
Large Scale Structures ◽  
Coherent Vortices ◽  
Scale Structures ◽  
Eddy Field

An analytical theory is developed which illustrates dynamics of the spontaneous generation of large-scale structures in the unforced two-dimensional eddying flows. The eddy field is represented by the closely packed array of standing coherent vortices whose intensity is weakly modulated by the long-wavelength perturbations introduced into the system. The asymptotic multiscale analysis makes it possible to identify instabilities resulting from the positive feedback of the background eddies on large-scale perturbations. Initially, these instabilities amplify at a rate proportional to the square root of their wavenumber. Linear growth is arrested when the amplitude of the long-wavelength perturbations reaches the level of background eddies. The subsequent evolutionary pattern is characterized by the emergence of relatively sharp features in the large-scale streamfunction field – features suggestive of the coherent jets commonly observed in eddying geophysical flows. The proposed solutions differ substantially from their counterparts in forced-dissipative systems, exemplified by the canonical model of Kolmogorov flow. The asymptotic model is successfully tested against numerical simulations.

Turbulent Mixing of Two Immiscible Fluids

2005 ◽  
Vol 127 (6) ◽  
pp. 1132-1139 ◽  
Author(s):  
Thierry Lemenand ◽  
Pascal Dupont ◽  
Dominique Della Valle ◽  
Hassan Peerhossaini
Keyword(s):  
Large Scale ◽  
High Efficiency ◽  
Size Distribution Function ◽  
Immiscible Fluids ◽  
Turbulent Dissipation ◽  
Large Scale Structures ◽  
Oil In Water ◽  
New Type ◽  
Turbulence Analysis ◽  
Favorable Conditions

The emulsification process in a static mixer HEV (high-efficiency vortex) in turbulent flow is investigated. This new type of mixer generates coherent large-scale structures, enhancing momentum transfer in the bulk flow and hence providing favorable conditions for phase dispersion. We present a study of the single-phase flow that details the flow structure, based on LDV measurements, giving access on the scales of turbulence. In addition, we discuss the liquid-liquid dispersion of oil in water obtained at the exit of the mixer/emulsifier. The generation of the dispersion is characterized by the Sauter diameter and described via a size-distribution function. We are interested in a local turbulence analysis, particularly the spatial structure of the turbulence and the turbulence spectra, which give information about the turbulent dissipation rate. Finally, we discuss the emulsifier efficiency and compare the HEV performance with existing devices.

scholarly journals A theory for the emergence of coherent structures in beta-plane turbulence

2014 ◽  
Vol 740 ◽  
pp. 312-341 ◽  
Author(s):  
Nikolaos A. Bakas ◽  
Petros J. Ioannou
Keyword(s):  
Turbulent Flows ◽  
Coherent Structures ◽  
Energy Input ◽  
Large Scale ◽  
Order Approximation ◽  
Plane Channel ◽  
Phase Speed ◽  
Homogeneous State ◽  
Zonal Jets ◽  
Beta Plane

AbstractPlanetary turbulent flows are observed to self-organize into large-scale structures such as zonal jets and coherent vortices. One of the simplest models of planetary turbulence is obtained by considering a barotropic flow on a beta-plane channel with turbulence sustained by random stirring. Nonlinear integrations of this model show that as the energy input rate of the forcing is increased, the homogeneity of the flow is broken with the emergence of non-zonal, coherent, westward propagating structures and at larger energy input rates by the emergence of zonal jets. We study the emergence of non-zonal coherent structures using a non-equilibrium statistical theory, stochastic structural stability theory (S3T, previously referred to as SSST). S3T directly models a second-order approximation to the statistical mean turbulent state and allows the identification of statistical turbulent equilibria and study of their stability. Using S3T, the bifurcation properties of the homogeneous state in barotropic beta-plane turbulence are determined. Analytic expressions for the zonal and non-zonal large-scale coherent flows that emerge as a result of structural instability are obtained. Through numerical integrations of the S3T dynamical system, it is found that the unstable structures equilibrate at finite amplitude. Numerical simulations of the nonlinear equations confirm the characteristics (scale, amplitude and phase speed) of the structures predicted by S3T.

scholarly journals S3T Stability of the Homogeneous State of Barotropic Beta-Plane Turbulence

2015 ◽  
Vol 72 (5) ◽  
pp. 1689-1712 ◽  
Author(s):  
Nikolaos A. Bakas ◽  
Navid C. Constantinou ◽  
Petros J. Ioannou
Keyword(s):  
Large Scale ◽  
Modulational Instability ◽  
Homogeneous State ◽  
Mean Flow ◽  
Large Scale Structures ◽  
Zonal Jets ◽  
Statistical Framework ◽  
Beta Plane ◽  
The Mean ◽  
Large Scale Flow

Abstract Zonal jets and nonzonal large-scale flows are often present in forced–dissipative barotropic turbulence on a beta plane. The dynamics underlying the formation of both zonal and nonzonal coherent structures is investigated in this work within the statistical framework of stochastic structural stability theory (S3T). Previous S3T studies have shown that the homogeneous turbulent state undergoes a bifurcation at a critical parameter and becomes inhomogeneous with the emergence of zonal and/or large-scale nonzonal flows and that these statistical predictions of S3T are reflected in direct numerical simulations. In this paper, the dynamics underlying the S3T statistical instability of the homogeneous state as a function of parameters is studied. It is shown that, for weak planetary vorticity gradient β, both zonal jets and nonzonal large-scale structures form from upgradient momentum fluxes due to shearing of the eddies by the emerging infinitesimal flow. For large β, the dynamics of the S3T instability differs for zonal and nonzonal flows but in both the destabilizing vorticity fluxes decrease with increasing β. Shearing of the eddies by the mean flow continues to be the mechanism for the emergence of zonal jets while nonzonal large-scale flows emerge from resonant and near-resonant triad interactions between the large-scale flow and the stochastically forced eddies. The relation between the formation of large-scale structure through modulational instability and the S3T instability of the homogeneous state is also investigated and it is shown that the modulational instability results are subsumed by the S3T results.

On the generation of large-scale eddy-driven patterns: the average eddy model

2016 ◽  
Vol 809 ◽  
pp. 316-344 ◽  
Author(s):  
Timour Radko
Keyword(s):  
Multiscale Analysis ◽  
Large Scale ◽  
Baroclinic Instability ◽  
Spontaneous Generation ◽  
Physical Processes ◽  
Layer System ◽  
Large Scale Structures ◽  
Wide Range ◽  
Scale Structures ◽  
Eddy Field

A theoretical model is developed which illustrates the dynamics of the spontaneous generation of large-scale structures in baroclinically unstable eddying flows. Techniques of asymptotic multiscale analysis are used to identify instabilities resulting from the positive feedback of the background eddies on large-scale perturbations. The novelty of the proposed approach lies in the choice of a dynamically consistent time-dependent background eddy field, which is taken from simulations of baroclinic instability in the Phillips two-layer system. The resulting solutions differ considerably from those of traditional multiscale models, in which the background eddy field is represented by steady analytical patterns. The present formulation makes it possible to (i) test the multiscale theory against the corresponding numerical simulations, (ii) unambiguously interpret the key physical processes at play and (iii) rationalize the emergence of large-scale patterns for certain background parameters. While the proposed approach to multiscale modelling is illustrated on a particular example of the Phillips baroclinic instability model, it is our belief that the presented technique is readily adaptable to a wide range of applications.

On the spacing of meandering jets in the strong-stair limit

2021 ◽  
Vol 930 ◽  
Author(s):  
R.K. Scott ◽  
B.H. Burgess ◽  
D.G. Dritschel
Keyword(s):  
Kinetic Energy ◽  
Large Scale ◽  
Complex Structure ◽  
Zonal Jets ◽  
Incomplete Mixing ◽  
Numerical Integrations ◽  
Coherent Vortices ◽  
Perfect Mixing ◽  
The Mean ◽  
Kinetic And Potential Energies

Based on an assumption of strongly inhomogeneous potential vorticity mixing in quasi-geostrophic $\beta$ -plane turbulence, a relation is obtained between the mean spacing of latitudinally meandering zonal jets and the total kinetic energy of the flow. The relation applies to cases where the Rossby deformation length is much smaller than the Rhines scale, in which kinetic energy is concentrated within the jet cores. The relation can be theoretically achieved in the case of perfect mixing between regularly spaced jets with simple meanders, and of negligible kinetic energy in flow structures other than in jets. Incomplete mixing or unevenly spaced jets will result in jets being more widely separated than the estimate, while significant kinetic energy outside the jets will result in jets closer than the estimate. An additional relation, valid under the same assumptions, is obtained between the total kinetic and potential energies. In flows with large-scale dissipation, the two relations provide a means to predict the jet spacing based only on knowledge of the energy input rate of the forcing and dissipation rate, regardless of whether the latter takes the form of frictional or thermal damping. Comparison with direct numerical integrations of the forced system shows broad support for the relations, but differences between the actual and predicted jet spacings arise both from the complex structure of jet meanders and the non-negligible kinetic energy contained in the turbulent background and in coherent vortices lying between the jets.

Some comments about observations and image processing of comet 29P/Schwassmann-Wachmann 1

1999 ◽  
Vol 173 ◽  
pp. 243-248
Author(s):  
D. Kubáček ◽  
A. Galád ◽  
A. Pravda
Keyword(s):  
Image Processing ◽  
Large Scale ◽  
Harvard College ◽  
Oak Ridge ◽  
Large Scale Structures ◽  
Short Period Comet ◽  
Short Period ◽  
Scale Structures ◽  
Harvard College Observatory ◽  
Period Comet

AbstractUnusual short-period comet 29P/Schwassmann-Wachmann 1 inspired many observers to explain its unpredictable outbursts. In this paper large scale structures and features from the inner part of the coma in time periods around outbursts are studied. CCD images were taken at Whipple Observatory, Mt. Hopkins, in 1989 and at Astronomical Observatory, Modra, from 1995 to 1998. Photographic plates of the comet were taken at Harvard College Observatory, Oak Ridge, from 1974 to 1982. The latter were digitized at first to apply the same techniques of image processing for optimizing the visibility of features in the coma during outbursts. Outbursts and coma structures show various shapes.

scholarly journals Fabrication of microcapsule extinguishing agent with core-shell structure for lithium-ions battery fire safety

2021 ◽  
Author(s):  
Weixin Zhang ◽  
Lin Wu ◽  
Dujin Qiao ◽  
Jie Tian ◽  
Yan Li ◽  
...  
Keyword(s):  
Large Scale ◽  
Urea Formaldehyde ◽  
Lithium Ion ◽  
Formaldehyde Resin ◽  
Shell Material ◽  
Lithium Ions ◽  
Safety Issues ◽  
Fire Extinguishing ◽  
New Type ◽  
Core Shell Structure

Safety issues limit the large-scale application of lithium-ion batteries. In this work, a new type of N-H-microcapsule fire extinguishing agent is prepared by using melamine-urea-formaldehyde resin as shell material, perfluoro(2-methyl-3-pentanone)...

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