scholarly journals 3D turbulent reconnection driven current-sheet dynamics: solar applications

2010 ◽  
Vol 6 (S274) ◽  
pp. 458-460
Author(s):  
Lapo Bettarini ◽  
Giovanni Lapenta
Keyword(s):  
Current Sheet ◽  
Characteristic Time ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Anomalous Effect ◽  
Instability Modes ◽  
Diffusive Dynamics ◽  
Three Dimensional Configuration ◽  
A Current ◽  
Dimensional Picture

AbstractWe provide a complete three-dimensional picture of the reconnecting dynamics of a current-sheet. Recently, a two-dimensional non-steady reconnection dynamics has been proved to occur without the presence of any anomalous effect (Lapenta, 2008, Skender & Lapenta, 2010, Bettarini & Lapenta, 2010) but such a picture must be confirmed in a full three-dimensional configuration wherein all instability modes are allowed to drive the evolution of the system, i.e. to sustain a reconnection dynamics or to push the system along a different instability path. Here we propose a full-space analysis allowing us to determine the longitudinal and, possibly, the transversal modes driving the different current-sheet disruption regimes, the corresponding characteristic time-scales and to study system's instability space- parameter (plasma beta, Lundquist and Reynolds numbers, system's aspect ratio). The conditions leading to an explosive evolution rather then to a diffusive dynamics as well as the details of the reconnection inflow/outflow regime at the disruption phase are determined. Such system embedded in a solar-like environment and undergoing a non-steady reconnection evolution may determine the formation both of jets and waves influencing the dynamics and energetic of the upper layers and of characteristic down-flows as observed in the low solar atmosphere.

Resistive MHD stagnation-point flows at a current sheet

1975 ◽  
Vol 14 (2) ◽  
pp. 283-294 ◽  
Author(s):  
B. U. Ö. Sonnerup ◽  
E. R. Priest
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Stagnation Point ◽  
Three Dimensional ◽  
Mhd Equations ◽  
Viscous Effects ◽  
Three Dimensional Flow ◽  
Merging Process ◽  
The Magnetic Field ◽  
A Current

A family of exact solutions to the MHD equations is presented for steady incompressible two- and three-dimensional flow in the vicinity of the stagnation point, which forms in a current sheet separating two colliding plasma streams. The magnetic field in each plasma is strictly parallel to the current sheet, but can have different magnitudes and directions. Resistive and viscous effects are accounted for. These flows are of considerable interest in connexion with the magnetic field merging process. They represent the limit of resistive field annihilation with zero reconnexion.

Symmetry breaking and instability mechanisms in medium depth torsionally driven open cylinder flows

2011 ◽  
Vol 672 ◽  
pp. 521-544 ◽  
Author(s):  
STUART J. COGAN ◽  
KRIS RYAN ◽  
GREGORY J. SHEARD
Keyword(s):  
Stability Analysis ◽  
Aspect Ratio ◽  
Symmetry Breaking ◽  
Axisymmetric Flow ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Interfacial Region ◽  
Nonlinear Stability Analysis ◽  
Aspect Ratios ◽  
Instability Modes

A numerical investigation was conducted into the different flow states, and bifurcations leading to changes of state, found in open cylinders of medium to moderate depth driven by a constant rotation of the vessel base. A combination of linear stability analysis, for cylinders of numerous height-to-radius aspect ratios (H/R), and nonlinear stability analysis and three-dimensional simulations for a cylinder of aspect ratio 1.5, has been employed. Attention is focused on the breaking of SO(2) symmetry. A comprehensive map of transition Reynolds numbers as a function of aspect ratio is presented by combining a detailed stability analysis with the limited existing data from the literature. For all aspect ratios considered, the primary instabilities are identified as symmetry-breaking Hopf bifurcations, occurring at Reynolds numbers well below those of the previously reported axisymmetric Hopf transitions. It is revealed that instability modes with azimuthal wavenumbers m = 1, 3 and 4 are the most unstable in the range 1.0 < H/R < 4, and that numerous double Hopf bifurcation points exist. Critical Reynolds numbers generally increase with cylinder aspect ratio, though a decrease in stability occurs between aspect ratios 1.5 and 2.0, where a local minimum in critical Reynolds number occurs. For H/R = 1.5, a detailed characterisation of instability modes is given. It is hypothesized that the primary instability leading to transition from steady axisymmetric flow to unsteady three-dimensional flow is related to deformation of shear layers that are present in the flow, in particular at the interfacial region between the vortex breakdown bubble and the primary recirculation.

scholarly journals Two- and three-dimensional wake transitions of an impulsively started uniformly rolling circular cylinder

2017 ◽  
Vol 826 ◽  
pp. 32-59 ◽  
Author(s):  
F. Y. Houdroge ◽  
T. Leweke ◽  
K. Hourigan ◽  
M. C. Thompson
Keyword(s):  
Stability Analysis ◽  
Circular Cylinder ◽  
Rapid Development ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Two Dimensional ◽  
Dimensional Flow ◽  
Instability Modes ◽  
Two Dimensional Flow ◽  
Lift And Drag

This paper presents the characteristics of the different stages in the evolution of the wake of a circular cylinder rolling without slipping along a wall at constant speed, acquired through numerical stability analysis and two- and three-dimensional numerical simulations. Reynolds numbers between 30 and 300 are considered. Of importance in this study is the transition to three-dimensionality from the underlying two-dimensional periodic flow and, in particular, the way that the associated transitions influence the fluid forces exerted on the cylinder and the development and the structure of the wake. It is found that the steady two-dimensional flow becomes unstable to three-dimensional perturbations at $Re_{c,3D}=37$, and that the transition to unsteady two-dimensional flow – or periodic vortex shedding – occurs at $Re_{c,2D}=88$, thus validating and refining the results of Stewart et al. (J. Fluid Mech. vol. 648, 2010, pp. 225–256). The main focus here is on Reynolds numbers beyond the transition to unsteady flow at $Re_{c,2D}=88$. From impulsive start up, the wake almost immediately undergoes transition to a periodic two-dimensional wake state, which, in turn, is three-dimensionally unstable. Thus, the previous three-dimensional stability analysis based on the two-dimensional steady flow provides only an element of the full story. Floquet analysis based on the periodic two-dimensional flow was undertaken and new three-dimensional instability modes were revealed. The results suggest that an impulsively started cylinder rolling along a surface at constant velocity for $Re\gtrsim 90$ will result in the rapid development of a periodic two-dimensional wake that will be maintained for a considerable time prior to the wake undergoing three-dimensional transition. Of interest, the mean lift and drag coefficients obtained from full three-dimensional simulations match predictions from two-dimensional simulations to within a few per cent.

Development and anisotropy of three-dimensional turbulence in a current sheet

2007 ◽  
Vol 14 (6) ◽  
pp. 062304 ◽  
Author(s):  
M. Onofri ◽  
P. Veltri ◽  
F. Malara
Keyword(s):  
Current Sheet ◽  
Three Dimensional ◽  
A Current

scholarly journals Diffusive dynamics and stochastic models of turbulent axisymmetric wakes

2015 ◽  
Vol 778 ◽  
Author(s):  
G. Rigas ◽  
A. S. Morgans ◽  
R. D. Brackston ◽  
J. F. Morrison
Keyword(s):  
Three Dimensional ◽  
Reynolds Numbers ◽  
Axisymmetric Body ◽  
Wake Flow ◽  
Model Parameters ◽  
Low Reynolds Numbers ◽  
Turbulent Fluctuations ◽  
Broken Symmetries ◽  
Diffusive Dynamics ◽  
Modelling Methodology

A modelling methodology to reproduce the experimental measurements of a turbulent flow in the presence of symmetry is presented. The flow is a three-dimensional wake generated by an axisymmetric body. We show that the dynamics of the turbulent wake flow can be assimilated by a nonlinear two-dimensional Langevin equation, the deterministic part of which accounts for the broken symmetries that occur in the laminar and transitional regimes at low Reynolds numbers and the stochastic part of which accounts for the turbulent fluctuations. Comparison between theoretical and experimental results allows the extraction of the model parameters.

Dancing without Space – On Nijinsky'sL'Après-midi d'un Faune(1912)

2009 ◽  
Vol 27 (1) ◽  
pp. 28-64 ◽  
Author(s):  
Hanna Järvinen
Keyword(s):  
Three Dimensional ◽  
Two Dimensional ◽  
Theatrical Space ◽  
Principal Character ◽  
Vaslav Nijinsky ◽  
Important Shift ◽  
Dimensional Picture

Three-dimensional theatrical space is often taken for granted as a precondition of dance. Already in 1912, the choreographer Vaslav Nijinsky provoked much discussion with a work that seemingly turned the performance into a moving, two-dimensional picture. L'Après-midi d'un Faune has achieved notoriety because of the objections some contemporary critics raised against the ‘immoral’ behaviour of the principal character, but I argue the style of the work brought about an important shift in how dancing was conceptualised as something composed by a choreographic author.

3D simulation of emulsion flow using the boundary element method on the heterogeneous computational systems

2012 ◽  
Vol 9 (1) ◽  
pp. 142-146
Author(s):  
O.A. Solnyshkina
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Problem Size ◽  
Low Reynolds Numbers ◽  
Infinite Domains ◽  
The Matrix ◽  
Computational Systems ◽  
Element Method

In this work the 3D dynamics of two immiscible liquids in unbounded domain at low Reynolds numbers is considered. The numerical method is based on the boundary element method, which is very efficient for simulation of the three-dimensional problems in infinite domains. To accelerate calculations and increase the problem size, a heterogeneous approach to parallelization of the computations on the central (CPU) and graphics (GPU) processors is applied. To accelerate the iterative solver (GMRES) and overcome the limitations associated with the size of the memory of the computation system, the software component of the matrix-vector product

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