Transport and Mixing in Kinematic and Dynamically Consistent Flows

2007 ◽  
Vol 64 (10) ◽  
pp. 3640-3651 ◽  
Author(s):  
P. H. Haynes ◽  
D. A. Poet ◽  
E. F. Shuckburgh
Keyword(s):  
Large Range ◽  
Vorticity Field ◽  
Transport Barrier ◽  
Multiple Jets ◽  
Mixing Behavior ◽  
Transport Barriers ◽  
Flow Evolution ◽  
Transport And Mixing ◽  
Dynamical Consistency ◽  
Strong Vorticity

Abstract The interplay between dynamics and transport in two-dimensional flows is examined by comparing the transport and mixing in a kinematic flow in which the velocity field is imposed as a given function of time with that in an analogous dynamically consistent flow in which the advected vorticity field controls the flow evolution. In both cases the variation of the transport and mixing behavior with a parameter ε governing the strength of the time dependence is considered. It is shown that dynamical consistency has the effect of (i) postponing the breaking of a central transport barrier as ε increases and (ii) removing the property of the kinematic flow that, for a large range of ε, a weakly permeable central barrier persists. The first effect is associated with the development of a strong vorticity gradient and the associated jet along the central transport barrier. The second effect is associated with the fact that, in the dynamically consistent flow, the breaking of the central barrier is accompanied by a drastic change in the vorticity field and hence in the structure of the flow. The relation between the vorticity field and transport barriers is further examined using a range of simple kinematic and dynamically consistent models. Implications for formulation of predictive models that represent the interactions between dynamics, transport, and mixing (and might be suggested as a basis for parameterizing eddies in flows that form multiple jets) are discussed.

Plasma-turbulence suppression and transport-barrier formation by externally driven radiofrequency waves in spherical tokamaks

2001 ◽  
Vol 65 (3) ◽  
pp. 235-253 ◽  
Author(s):  
K. KOMOSHVILI ◽  
S. CUPERMAN ◽  
C. BRUMA
Keyword(s):  
Electric Fields ◽  
Turbulent Transport ◽  
Plasma Turbulence ◽  
Ion Temperature ◽  
Transport Barrier ◽  
Ion Temperature Gradient ◽  
Turbulence Suppression ◽  
Barrier Formation ◽  
Transport Barriers ◽  
Fast Waves

Turbulent transport of heat and particles is the principle obstacle confronting controlled fusion today. We investigate quantitatively the suppression of turbulence and formation of transport barriers in spherical tokamaks by sheared electric fields generated by externally driven radiofrequency (RF) waves, in the frequency range ωA ∼ ω < ωci (where ωA and ωci are the Alfvén and ion cyclotron frequencies).This investigation consists of the solution of the full-wave equation for a spherical tokamak in the presence of externally driven fast waves and the evaluation of the power dissipation by the mode-converted Alfvén waves. This in turn provides a radial flow shear responsible for the suppression of plasma turbulence. Thus a strongly nonlinear equation for the radial sheared electric field is solved, and the turbulent transport suppression rate is evaluated and compared with the ion temperature gradient (ITG) instability increment.

scholarly journals Material barriers to diffusive and stochastic transport

2018 ◽  
Vol 115 (37) ◽  
pp. 9074-9079 ◽  
Author(s):  
George Haller ◽  
Daniel Karrasch ◽  
Florian Kogelbauer
Keyword(s):  
Coherent Structures ◽  
Fluid Transport ◽  
Order Term ◽  
Velocity Fields ◽  
Leading Order ◽  
Transport Barrier ◽  
Material Surfaces ◽  
Stochastic Transport ◽  
Transport Barriers ◽  
Enhancer Detection

We seek transport barriers and transport enhancers as material surfaces across which the transport of diffusive tracers is minimal or maximal in a general, unsteady flow. We find that such surfaces are extremizers of a universal, nondimensional transport functional whose leading-order term in the diffusivity can be computed directly from the flow velocity. The most observable (uniform) transport extremizers are explicitly computable as null surfaces of an objective transport tensor. Even in the limit of vanishing diffusivity, these surfaces differ from all previously identified coherent structures for purely advective fluid transport. Our results extend directly to stochastic velocity fields and hence enable transport barrier and enhancer detection under uncertainties.

scholarly journals Impact of the 2009 major sudden stratospheric warming on the composition of the stratosphere

2015 ◽  
Vol 15 (15) ◽  
pp. 8695-8715 ◽  
Author(s):  
M. Tao ◽  
P. Konopka ◽  
F. Ploeger ◽  
J.-U. Grooß ◽  
R. Müller ◽  
...  
Keyword(s):  
Potential Temperature ◽  
Lagrangian Model ◽  
Boreal Winter ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Transport Barrier ◽  
Mixing Parameters ◽  
Downward Propagation ◽  
Transport And Mixing ◽  
The Tropics

Abstract. In a case study of a remarkable major sudden stratospheric warming (SSW) during the boreal winter 2008/09, we investigate how transport and mixing triggered by this event affected the composition of the entire stratosphere in the Northern Hemisphere. We simulate this event with the Chemical Lagrangian Model of the Stratosphere (CLaMS), both with optimized mixing parameters and with no mixing, i.e. with transport occurring only along the Lagrangian trajectories. The results are investigated by using tracer–tracer correlations and by applying the transformed Eulerian-mean formalism. The CLaMS simulation of N2O and O3, and in particular of the O3–N2O tracer correlations with optimized mixing parameters, shows good agreement with the Aura Microwave Limb Sounder (MLS) data. The spatial distribution of mixing intensity in CLaMS correlates fairly well with the Eliassen–Palm flux convergence. This correlation illustrates how planetary waves drive mixing. By comparing simulations with and without mixing, we find that after the SSW, poleward transport of air increases, not only across the vortex edge but also across the subtropical transport barrier. Moreover, the SSW event, at the same time, accelerates polar descent and tropical ascent of the Brewer–Dobson circulation. The accelerated ascent in the tropics and descent at high latitudes first occurs in the upper stratosphere and then propagates downward to the lower stratosphere. This downward propagation takes over 1 month from the potential temperature level of 1000 to 400 K.

scholarly journals Transport Barrier Triggered by Resonant Three-Wave Processes Between Trapped-Particle-Modes and Zonal Flow

Plasma ◽  
2019 ◽  
Vol 2 (2) ◽  
pp. 229-257
Author(s):  
Alain Ghizzo ◽  
Daniele Del Sarto
Keyword(s):  
Low Frequency ◽  
Zonal Flow ◽  
Hamiltonian Reduction ◽  
Transport Barrier ◽  
Drift Wave Turbulence ◽  
Parametric Decay ◽  
Resonant Wave ◽  
New Findings ◽  
Transport Barriers ◽  
Gyrokinetic Simulations

We address the mechanisms underlying low-frequency zonal flow generation in a turbulent system through the parametric decay of collisionless trapped particle modes and its feedback on the stabilization of the system. This model is in connection with the observation of barrier transport in reduced gyrokinetic simulations (A. Ghizzo et al., Euro. Phys. Lett. 119(1), 15003 (2017)). Here the analysis is extended with a detailed description of the resonant mechanism. A key role is also played by an initial polarisation source that allows the emergence of strong initial shear flow. The parametric decay leads to the growth of a zonal flow which differs from the standard zero frequency zonal flow usually triggered by the Reynolds stress in fluid drift-wave turbulence. The resulting zonal flow can oscillate at low frequency close to the ion precession frequency, making it sensitive to strong amplification by resonant kinetic processes. The system becomes then intermittent. These new findings, obtained from numerical experiments based on reduced semi-Lagrangian gyrokinetic simulations, shed light on the underlying physics coming from resonant wave-particle interactions for the formation of transport barriers. Numerical simulations are based on a Hamiltonian reduction technique, including magnetic curvature and interchange turbulence, where both fastest scales (cyclotron and bounce motions) are gyro-averaged.

FORMATION OF TRANSPORT BARRIER BY SHEARING

2004 ◽  
Vol 18 (12n13) ◽  
pp. 551-571 ◽  
Author(s):  
EUN-JIN KIM
Keyword(s):  
Turbulent Transport ◽  
Transport Barrier ◽  
Zonal Flows ◽  
Barrier Formation ◽  
Laboratory Plasmas ◽  
Transport Barriers

We review the effect of shearing on transport and the formation of transport barriers. The focus is primarily on laboratory plasmas where the formation of transport barriers (the L–H transition) is thought to originate from the turbulence regulation due to both (coherent) mean and (random) zonal flows. We provide quantitative discussion on the reduction of turbulent transport by these flows and elucidate their roles in the barrier formation.

scholarly journals Vertical Transition in Transport and Mixing in Baroclinic Flows

2008 ◽  
Vol 65 (4) ◽  
pp. 1137-1157 ◽  
Author(s):  
M. D. Greenslade ◽  
P. H. Haynes
Keyword(s):  
Relaxation Rate ◽  
Channel Model ◽  
Gaussian Function ◽  
Plane Channel ◽  
Lower Boundary ◽  
Thermal Relaxation ◽  
Vertical Shear ◽  
Large Set ◽  
Transport Barrier ◽  
Transport And Mixing

Abstract Numerical simulations in multilevel baroclinic turbulence in a β-plane channel model are discussed, focusing on the transport and mixing behavior. The temperature field in the model is relaxed toward a field consistent with a broad zonal jet with vertical shear that is a Gaussian function of the cross-channel coordinate. The resulting statistical equilibrium flow includes an active baroclinic eddy field. The transport and mixing properties are analyzed by considering the fields of potential vorticity and a passive tracer (from which effective diffusivities/equivalent lengths are calculated). The upper part of the flow organizes itself in such a way that there is a transport barrier in the center of the channel, with eddy mixing regions on either side. In the lower part of the flow the eddy mixing occurs across a single broad region, with no central transport barrier. The transition between these two regimes takes place abruptly at a height zT. A large set of simulations is used to map out the variation of zT as a function of external parameters including β, the thermal relaxation rate κT, and the (lower boundary) frictional relaxation rate κM (applied in the lowest model layer only). The transition height zT is argued to be relevant to sharp vertical transitions in transport and mixing observed in atmospheric and oceanic flows.

scholarly journals Tokamak Edge Plasma Turbulence Interaction with Magnetic X-Point in 3D Global Simulations

Fluids ◽  
2019 ◽  
Vol 4 (1) ◽  
pp. 50 ◽  
Author(s):  
Davide Galassi ◽  
Guido Ciraolo ◽  
Patrick Tamain ◽  
Hugo Bufferand ◽  
Philippe Ghendrih ◽  
...  
Keyword(s):  
Turbulent Transport ◽  
Edge Plasma ◽  
Turbulent Structures ◽  
Magnetic Shear ◽  
Transport Barrier ◽  
Fluid Turbulence ◽  
Transport Barriers ◽  
Tokamak Edge ◽  
The Impact

Turbulence in the edge plasma of a tokamak is a key actor in the determination of the confinement properties. The divertor configuration seems to be beneficial for confinement, suggesting an effect on turbulence of the particular magnetic geometry introduced by the X-point. Simulations with the 3D fluid turbulence code TOKAM3X are performed here to evaluate the impact of a diverted configuration on turbulence in the edge plasma, in an isothermal framework. The presence of the X-point is found, locally, to affect both the shape of turbulent structures and the amplitude of fluctuations, in qualitative agreement with recent experimental observations. In particular, a quiescent region is found in the divertor scrape-off layer (SOL), close to the separatrix. Globally, a mild transport barrier spontaneously forms in the closed flux surfaces region near the separatrix, differently from simulations in limiter configuration. The effect of turbulence-driven Reynolds stress on the formation of the barrier is found to be weak by dedicated simulations, while turbulence damping around the X-point seems to globally reduce turbulent transport on the whole flux surface. The magnetic shear is thus pointed out as a possible element that contributes to the formation of edge transport barriers.

scholarly journals The rarefied (non-continuum) conditions of tracer particle transport in soils, with implications for assessing the intensity and depth dependence of mixing from geochronology

2018 ◽  
Author(s):  
David Jon Furbish ◽  
Rina Schumer ◽  
Amanda Keen-Zebert
Keyword(s):  
Particle Transport ◽  
Tracer Particle ◽  
Planck Equation ◽  
Strong Mixing ◽  
Surface Erosion ◽  
Soil Thickness ◽  
Particle Mixing ◽  
Mixing Intensity ◽  
Mixing Behavior ◽  
Transport And Mixing

Abstract. We formulate tracer particle transport and mixing in soils due to disturbance driven particle motions in terms of the Fokker-Planck equation. The probabilistic basis of the formulation is suitable for rarefied particle conditions, and for parsing the mixing behavior of extensive and intensive properties belonging to the particles rather than to the bulk soil. The significance of the formulation is illustrated with the examples of vertical profiles of expected 10Be concentrations and particle OSL ages for the benchmark situation involving a one-dimensional mean upward soil motion with nominally steady surface erosion in the presence of either uniform or depth dependent particle mixing, and varying mixing intensity. The analysis, together with Eulerian-Lagrangian numerical simulations of tracer particle motions, highlight the significance of calculating ensemble expected values of extensive and intensive particle properties, including higher moments of particle OSL ages, rather than assuming de facto a continuum-like mixing behavior, with implications for field sampling and for describing the mixing behavior of other particle and soil properties. Profiles of expected 10Be concentrations and OSL ages systematically vary with mixing intensity as measured by a Peclet number involving the speed at which particles enter the soil, the soil thickness, and the particle diffusivity. Profiles associated with uniform mixing versus a linear decrease in mixing with depth are distinct for moderate mixing, but become similar with either weak mixing or strong mixing; uniform profiles do not necessarily imply uniform mixing.

LOCALIZING TRANSPORT BARRIERS IN DEGENERATE 3/2 D.O.F. HAMILTONIAN SYSTEMS WITH APPLICATIONS TO MAGNETIC CONFINEMENT FUSION

2013 ◽  
Vol 23 (02) ◽  
pp. 1350034 ◽  
Author(s):  
DANA CONSTANTINESCU ◽  
MARIE-CHRISTINE FIRPO
Keyword(s):  
Hamiltonian Systems ◽  
Degrees Of Freedom ◽  
Magnetic Confinement ◽  
Tokamak Plasmas ◽  
Transport Barrier ◽  
Magnetic Confinement Fusion ◽  
Hamiltonian Models ◽  
Transport Barriers ◽  
Confinement Fusion ◽  
Degenerate Hamiltonian Systems

The existence of transport barriers in 3/2 degrees of freedom degenerate Hamiltonian systems is studied using the associated stroboscopic maps. For small enough amplitudes of the perturbations, a transport barrier (formed by infinitely many invariant rotational circles) is proven to exist and to form in the degenerate annulus. These results are applied to Hamiltonian models which describe some magnetic configurations in tokamak plasmas.

A numerical study of quasi-geostrophic flow over isolated topography

1985 ◽  
Vol 154 ◽  
pp. 231-252 ◽  
Author(s):  
J. Verron ◽  
C. Le Provost
Keyword(s):  
Numerical Study ◽  
Wave Pattern ◽  
Open Boundary ◽  
Open Boundary Conditions ◽  
Vorticity Field ◽  
Transient Regimes ◽  
Barotropic Flow ◽  
Detailed Simulation ◽  
Strong Vorticity ◽  
Zonal Waves

An extensive set of numerical simulations is performed to synthesize the behaviour of a barotropic flow over isolated topography on an f-plane and on a β-plane. The model is based on the quasi-geostrophic vorticity equation, where the dissipation terms have been retained. The use of open boundary conditions. following the method described by Orlanski (1976), allows detailed simulation of time-dependent flows over long periods.On the f-plane, the ultimate solution is always characterized by a typical vorticity field with an anticyclonic vortex trapped over the topography, but different transient regimes occur, related to the importance of advection versus topography effect: direct advection of the positive vortex for strong flows; eddy interactions and double-vortex-structure appearance for weaker flows; oscillatory regimes with topographic trapped-waves generation for very strong vorticity-interaction cases.On the β-plane, and for prograde flows, the situation is complicated by a Rossby wave pattern extending mainly downstream but also having an upstream component corresponding to zonal waves. For retrograde flows the obstacle does not excite Rossby waves but a transient response with zonal waves whose lifetime depends on the nonlinearity.

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