Turbulent Plasma Flow Research Articles

Wavelet transforms and their applications to MHD and plasma turbulence: a review

Wavelet analysis and compression tools are reviewed and different applications for the study of MHD and plasma turbulence are presented. We introduce the continuous and the orthogonal wavelet transform and detail several statistical diagnostics based on the wavelet coefficients. We then show how to extract coherent structures out of fully developed turbulent flows using wavelet-based denoising. Finally some multiscale numerical simulation schemes using wavelets are described. Several examples for analysing, compressing and computing one-, two- and three-dimensional turbulent MHD or plasma flows are presented.

Large-Eddy Simulation of Subsonic-Supersonic Flow and Heat Transfer in a Hybrid Gas-Water Stabilized Arc

The paper presents numerical simulations of the turbulence effect in the discharge and near-outlet regions of the hybrid-stabilized argon-water electric arc. Calculations were carried out for the assumption of laminar and turbulent plasma flow models, respectively. Results of simulation for currents 300-600 A on a fine numerical grid show that the influence of turbulence is weak and the maximum difference for all the monitored physical quantities is less than 2% in the discharge region and less than 6% in the near-outlet region. Comparison with experimental temperature profiles exhibits good agreement.

Investigating Plasma Jets Behavior using Axisymmetric Lattice Boltzmann Model under Temperature Dependent Viscosity

AbstractThis study aims to investigate turbulent plasma flow using the lattice Boltzmann (LB) method. A double population model D2Q9-D2Q4 is employed to calculate the plasma velocity and temperature fields. Along with the calculation process a conversion procedure is made between the LB and the physical unit systems, so that thermo-physical properties variation is fully accounted for and the convergence is checked in physical space. The configuration domain and the boundary condition treatment are selected based on the most cited studies in order to illustrate a realistic situation. The jet morphology analysis gives credible results by comparison with commonly published works. It was demonstrated also that accounting for the substrate as wall boundary condition modify greatly the flow and temperature structures with may affect absolutely the particles behavior during its in-flight in the hot gas.

Advanced Validation of Nonequilibrium Plasma Flow Simulation for Arc-Heated Wind Tunnels

Turbulent plasma flows in arc heaters, such as Japan Aerospace Exploration Agency’s 750 kW, NASA’s 20 MW, and Kyushu University’s 20 kW facilities, were investigated, and the distributions of the flowfield properties were successfully obtained. The arc discharge in the constrictor section and the expansion processes in the nozzle section played key roles in the formation of an arc-heated flow. Hence, for accurately predicting high-enthalpy flow properties, it was important to correctly model the complex phenomena observed in various-scale facilities. For this purpose, an integrated analysis model to simulate various-scale arc-heated flows with high accuracy was developed. The turbulent flowfield was described using the Reynolds-averaged Navier–Stokes equations with a multitemperature model, which was tightly coupled with electric-field and radiation-field calculations. A sophisticated and low-cost radiation model and a low-Reynolds-number two-equation turbulence model were introduced into the flowfield simulation. To validate the present integrated analysis model, the computed results were compared with the corresponding experimental data for the mass-averaged enthalpy, the translational and rotational temperatures, and the number density of nitrogen obtained through spectroscopic and laser-induced fluorescence techniques. Moreover, the mechanisms of energy input by discharge and energy loss are discussed, along with the distributions of the electronic excitation temperature and heat flux on the constrictor wall derived from the arc column. Although the results indicated that a relatively detailed discharge model is required to describe the arc discharge with relatively high accuracy, the present flowfield model was generally in good agreement with various operating conditions of the facilities.

The Influence of Turbulence on Characteristics of a Hybrid-Stabilized Argon-Water Electric Arc

The paper presents numerical simulations of the discharge and near outlet regions of the hybrid-stabilized argon-water electric arc. Calculations were carried out for the assumption of laminar and turbulent plasma flow models, respectively. Results of calculations for currents 300-600 A show that the influence of turbulence is weak and the maximum difference for all the monitored physical quantities is less than 10%. Comparison with available experiments exhibits good agreement.

A lattice Boltzmann-based investigation of powder in-flight characteristics during APS process, part I: modelling and validation

This study aims to investigate turbulent plasma flow over spheroidal particles using the lattice Boltzmann (LB) method. A double population model D2Q9-D2Q4 is employed to calculate the plasma velocity and temperature fields. Along with the calculation process a conversion procedure is made between the LB and the physical unit systems, so that thermo-physical properties variation is fully accounted for and the convergence is checked in physical space. The configuration domain and the boundary condition treatment are selected based on the most cited studies in order to illustrate a realistic situation. The jet morphology analysis gives credible results by comparison with commonly published works. A second Lagrangian model has been developed to investigate the plasma-particles exchange during its in-flight. The tracking of the μ-sized particles allows concluding that our results are in sufficient agreement with those of the Jets&Poudres code and that the LB method account well for plasma jet physics which affects directly the particles in-flights.

Preparation and Properties of Ultra-High Temperature Ceramics Based on ZrC and HfC

Successful preparation of massive compact bodies from ultra-high temperature ceramics like zirconium carbide, hafnium carbide and their cermets with tungsten matrix with high values of mechanical parameters is difficult. Only limited number of techniques is able to perform it because of their absolutely highest melting points. In our contribution the preparation of these materials by both - hot pressing and plasma spraying techniques is described and chemical processes taking part at the fabrication are studied. Hot-pressed products fabricated at 2000°C and 6 GPa partly react with the internal surface of the BELT-type apparatus. Melting and solidification is taking place at plasma spraying. This process, carried out by water stabilized plasma torch with centerline temperature up to 30 000°C, is joined with undesirable reactions with plasma-forming medium, with oxidation in a turbulent plasma flow and nitridation of free-flight particles. All these chemical processes depend on variety of parameters, such as particle size of the feedstock powders or electric power of the arc. The mentioned parameters are easily controlled. Other, less controllable, factors include trajectory of powder particles in the plasma jet, important for the melting degree as well as for oxidation or nitridation of the powder surface. New knowledge concerning properties of compact ZrC and HfC were obtained.

Turbulence and radiation behaviours in large-scale arc heaters

Turbulent plasma flow in large-scale arc heaters such as JAXA 750 kW and NASA 20 MW facilities was investigated and distributions of flow-field properties were successfully obtained. The turbulent flow field was described by the Navier–Stokes equations with a multitemperature model, which was tightly coupled with electric-field and radiation-field calculations. An accurate and low-cost radiation model, and a low Reynolds number two-equation turbulence model were introduced into the flow-field simulation. It was confirmed that the plasma flows in the arc-heating facilities were in a highly thermochemical nonequilibrium state in the expansion section and that the arc discharge plays a critical role in the heating section. It was quantitatively clarified that radiation and turbulence phenomena were very important in transferring heat and momentum from the high-temperature flow near the core to the cold gas region near the facility wall. To confirm the effectiveness of the present numerical model, the obtained results were compared with experimental data for the arc voltage, mass-averaged enthalpy, chamber pressure and heat efficiency. The present flow-field model was found to give good agreement for various operating conditions of the facilities.

Small-scale kinematic dynamo and non-dynamo in inertial-range turbulence

We investigate the Lagrangian mechanism of the kinematic ‘fluctuation’ magnetic dynamo in a turbulent plasma flow at small magnetic Prandtl numbers. The combined effect of turbulent advection and plasma resistivity is to carry infinitely many field lines to each space point, with the resultant magnetic field at that point given by the average over all the individual line vectors. As a consequence of the roughness of the advecting velocity, this remains true even in the limit of zero resistivity. We show that the presence of the dynamo effect requires sufficient angular correlation of the passive line vectors that arrive simultaneously at the same space point. We illustrate this in detail for the Kazantsev–Kraichnan model of the kinematic dynamo with a Gaussian advecting velocity that is spatially rough and white noise in time. In the regime where dynamo action fails, we also obtain the precise rate of decay of the magnetic energy. These exact results for the model are obtained by a generalization of the ‘slow-mode expansion’ of Bernard, Gawȩdzki and Kupiainen to non-Hermitian evolution. Much of our analysis applies also to magnetohydrodynamic turbulence.

Laminar/Turbulent Plasma Jets Generated at Reduced Pressure

Laminar DC plasma jets are attractive for precisely controlled plasma-material processing. The design of a novel nontransferred plasma torch enabled the switching between turbulent and laminar plasma flows by simply changing the plasma generation parameters. Images of the plasma flows generated at different conditions are presented.

An Integrated Exploration Approach to Visualizing Multivariate Particle Data

The authors describe a data exploration system that visualizes time-varying, multivariate, point-based data from gyrokinetic particle simulations. By using two interaction modes, their system lets researchers explore collections of densely packed particles and discover interesting aspects, such as the location and motion of particles trapped in turbulent plasma flow.

Thermodynamic model of MHD turbulence and some of its applications to accretion disks

Here the basic concepts of stellar-planetary cosmogony, the problem of reconstructing the evolution of a protoplanetary gas-dust cloud by taking into account electrodynamic effects are addressed. A closed system of magnetohydrodynamic (MHD) equations of mean motion designed to model shear and convective turbulent flows in electrically conducting media in the presence of a magnetic field is derived in the approximation of single-fluid magnetohydrodynamics. These equations can be used for a numerical solution of the problems on mutually consistent modeling of powerful turbulent cosmic plasma flows in accretion disks and related coronas in which the magnetic field affects significantly the dynamics of occurring astrophysical processes. When developing the model of a conducting turbulized medium, in addition to the traditional probability-theoretic averaging of the MHD equations, we also systematically use the weighted Favre averaging. The latter allows the form of the averaged equations of motion for a compressible electrically conducting fluid and the analysis of the mechanisms for the amplification of macroscopic fields by turbulent flows to be simplified considerably. For a clear physical interpretation of the individual components of the plasma-field energy balance, we derive various energy equations that allow us to trace the possible transitions of energy from one form to another and, in particular, to understand the mechanisms for the transfer of the gravitational and kinetic energies of mean motion to magnetic energy.

Instability results related to compressible Korteweg system

This paper presents the study of surface tension effects in compressible mixtures in the framework of diffuse interface models. In the first part, we describe results previously obtained on the so-called compressible Korteweg and shallow water models and we present nonlinear stability using energy estimates and a new entropy equality recently discovered. These diffuse interface models also allow to take account of capillarity effects in turbulent mixtures and plasma flows subject to Rayleigh–Taylor instabilities. The aim of the last part is to study the influence of surface tension on this instability phenomena. More precisely we look at the expression of the growth rate under a small perturbation of wave number k. We prove that for an appropriate choice of the capillary number σ in terms on the surface tension coefficient T s (that means particular pressure laws), we find the same expression as for the two incompressible fluids model with surface tension coefficient on a sharp interface studied for instance by Chandrasekhar (Hydrodynamic and hydromagnetic stability. Dover Publications, Inc. New York, 1981).

Comparative study of two- and three-dimensional modeling on arc discharge phenomena inside a thermal plasma torch with hollow electrodes

A comparative study between two- and three-dimensional (2D and 3D) modeling is carried out on arc discharge phenomena inside a thermal plasma torch with hollow electrodes, in order to evaluate the effects of arc root configuration characterized by either 2D annular or 3D highly localized attachment on the electrode surface. For this purpose, a more precise 3D transient model has been developed by taking account of 3D arc current distribution and arc root rotation. The 3D simulation results apparently reveal that the 3D arc root attachment brings about the inherent 3D and turbulence nature of plasma fields inside the torch. It is also found that the constricted arc column near the vortex chamber plays an important role in heating and acceleration of injected arc gases by concentrating arc currents on the axis of the hollow electrodes. The inherent 3D nature of arc discharge is well preserved inside the cathode region, while these 3D features slowly diminish behind the vortex chamber where the turbulent flow begins to be developed in the anode region. Based on the present simulation results, it is noted that the mixing effects of the strong turbulent flow on the heat and mass transfer are mainly responsible for the gradual relaxation of the 3D structures of plasma fields into the 2D axisymmetric ones that eventually appear in the anode region near the torch exit. From a detailed comparison of the 3D results with the 2D ones, the arc root configuration seems to have a significant effect on the heat transfer to the electrode surfaces interacting with the turbulent plasma flow. That is, in the 2D simulation based on an axisymmetric stationary model, the turbulence phenomena are fairly underestimated and the amount of heat transferred to the cold anode wall is calculated to be smaller than that obtained in the 3D simulation. For the validation of the numerical simulations, calculated plasma temperatures and axial velocities are compared with experimentally measured ones, and the 3D simulation turns out to be more accurate than the 2D simulation as a result of a relatively precise description of the turbulent phenomena inside the torch using a more realistic model of arc root attachment. Finally, it is suggested that the 3D transient formulation is indeed required for describing the real arc discharge phenomena inside the torch, while the 2D stationary approach is sometimes useful for getting practical information about the time-averaged plasma characteristics outside the torch because of its simplicity and rapidness in computation.

Multiscaling Dynamics of Impurity Transport in Drift-Wave Turbulence

Intermittency effects and the associated multiscaling spectrum of exponents are investigated for impurities advection in tokamak edge plasmas. The two-dimensional Hasagawa-Wakatani model of resistive drift-wave turbulence is used as a paradigm to describe edge tokamak turbulence. Impurities are considered as a passive scalar advected by the plasma turbulent flow. The use of the extended self-similarity technique shows that the structure function relative scaling exponent of impurity density and vorticity follows the She-Leveque model. This confirms the intermittent character of the impurities advection in the turbulent plasma flow and suggests that impurities are advected by vorticity filaments.

Multiple cusps during an extended northward IMF period with a significant By component

On 21–22 March 2001, four cusp‐like regions were observed consecutively in about five hours by all four Cluster spacecraft when the interplanetary magnetic field (IMF) was northward with a significant By component. All four cusp‐like encounters were characterized by turbulent magnetic fields, high‐density plasma, and plasma flow significantly slower than the magnetosheath level. The cusp‐like regions are associated with thermalized, bidirectional distributed plasma electrons. The first encountered cusp is the main cusp; the other three cusp‐like regions are temporal effects. The normal velocities vn at boundary interfaces (exit from the cusp) are found to be almost three times larger than that at boundary interfaces (entry into the cusp). The boundary normal, velocity, and timing analysis for six clear boundaries of the last three cusps obtained by all four spacecraft indicates that they are most likely one boundary shifting in the dawn‐dusk direction between the dayside magnetosphere/trapping region and the cusp region. So the Cluster spacecraft have been observing the same cusp, and it appeared as four cusp‐like regions due to possible magnetospheric oscillations. Oscillations with a period of 22 min are observed by the Cluster spacecraft in the high‐latitude region, which is in agreement with the cold‐dense plasma sheet fluctuations (20 min period) observed by the Geotail satellite. Multiple cusps observed by Cluster and the wavy‐like structures in the dusk low‐latitude boundary layer observed by Geotail simultaneously suggest the whole magnetosphere is oscillating during northward IMF.

Some features of the plasma flow in the magnetosheath behind quasi-parallel and quasi-perpendicular bow shocks

Variations of the ion flux and magnetic field magnitude in the undisturbed solar wind, in the foreshock, and in the magnetosheath have been examined using simultaneous measurements on the INTERBALL-1, IMP 8, WIND and ACE spacecraft. A high-time resolution of INTERBALL-1 measurements has allowed us to observe variations of these parameters in a broad range of frequencies (0.01–1 Hz). In this frequency range, magnetosheath plasma and field parameters fluctuate with very large amplitudes and are subjected to extremely intensive variations even during “quiet” conditions in the solar wind. The dependence of magnetosheath variations on the interplanetary magnetic field (IMF) direction was investigated. It was found that during the quasi-parallel IMF orientation to the bow shock normal (i.e., when Θ Bn < 45 ∘ ), an increase in the amplitude of variations of the ion flux and magnetic field is observed not only ahead of the bow shock (in the foreshock region) but also behind it, i.e., in the magnetosheath. The Θ Bn angle turned out to be the parameter, which significantly affects the properties of the turbulent plasma flow. An application of a spectral analysis allowed us to show substantial differences in the frequency properties of variations of the ion flux and magnetic field magnitude in the undisturbed solar wind, foreshock, and magnetosheath (separately for the quasi-parallel and quasi-perpendicular conditions of the bow shock).

Critical Reynolds number in plasma flows on a stabilized plasmatron section

A technique for determining the criterion of transition from the laminar to the turbulent flow regime on a stabilized plasmatron channel section is proposed. The technique uses experimental data and the methods of numerical simulation of plasma flows. A criterial generalization of the experimental data which for the first time makes it possible to establish the boundary of transition from the laminar to the turbulent flow regime on a stabilized plasmatron channel section is proposed. The experimental results are in good agreement with the theoretical dependences derived in the study. A curve (analog of the neutral curve) separating the domains of existence of laminar and turbulent plasma flows in a cylindrical channel is constructed in the space of the plasmatron working parameters.

Thermodynamic analysis and numerical resolution of a turbulent - fully ionized plasma flow model

This paper is devoted to the modeling and numerical resolution of a non-dissipative compressible turbulent plasma flow model involving three temperatures (turbulence, ions and electrons). The first step is to derive such a model. To do this, an analysis of the Reynolds averaged Euler equations (the k-model) is carried out. It is shown that thermodynamic requirements enable the derivation of an equation of state for turbulent variables. This equation of state is of the same type as those of an ideal gas. In this context, the various thermodynamic variables of turbulence can be obtained (energy, pressure, temperature etc.). This hyperbolic conservative model has exactly the same structure as the two temperatures plasma model of Zel’dovich. Thanks to the clear structure of these two models, the turbulent plasma model is derived and involves three temperatures. The second step is to derive an accurate numerical scheme for its solution. A linearized Riemann solver and a positive HLLC type solver are derived and embedded into a conventional Godunov scheme. It is shown that this method requires important corrections to preserve contact discontinuities and temperatures monotonicity. The corrections are based upon a non-conservative formulation of the turbulence and electrons energy equations, while total energy conservation is preserved. The modified method behaves correctly with contacts and shocks.

Low Altitude Cusp–Cleft Region Signatures of Strong Geomagnetic Disturbances

The polar cusp being a region of the free access of the solar wind into the inner magnetosphere is also the site of turbulent plasma flow. The cusp area at low altitudes acts like a focus of a variety type of instability and disturbances from different regions of the Earth. Daily f0F2 frequencies are discussed regarding the cusp position. The high time resolution wave measurements together with electron and ion energetic spectra measurements registered on the board the Freja satellite and Magion-3 and the electron density at the peak of f0F2 layers collected from ground-based ionosonde measurements were used to study the response of ionospheric plasma within the cusp–cleft region to the strong geomagnetic storm. In this paper we present the response of the ionospheric plasma to the disturbed conditions seen in the topside wave measurements and in the ionospheric characteristics maps obtained from the ground-based VI network. The need of the cusp feature model for radio communication purposes is advocated.