Cylindrical MHD induction device in the “ideal pressure source” regime

The causes for the onset of a specific operating regime of MHD induction devices which arises after a loss of stability of the uniform flow are investigated. A modification of the original method of studying singularly perturbed dynamical systems in the neighborhood of a bifurcation point is used to construct the asymptotic behavior of the characteristic pressure for various limiting cases. Zh. Tekh. Fiz. 67, 5–9 (June 1997)     

Negative magnetic viscosity in two dimensions

The occurrence of “negative viscosities” is studied within the framework of two-dimensional magnetohydrodynamics MHD. We use assumptions which are typical when studying the effects of smaller-scale fields on larger-scale ones, namely, the small-scale MHD fields are assumed to be sufficiently weak, jointly stationary, homogeneous, and maintained by external sources. The criteria of large-scale field generation due to negative viscosities are derived for various special forms of isotropic small-scale fields as well as anisotropic ones; the latter can be regarded as MHD stochastic analogs of the known Kolmogorov flow. Zh. éksp. Teor. Fiz. 116, 1264–1286 (October 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

The role of helicity in turbulent MHD flows

We have studied the behavior of a helical homogeneous small-scale MHD turbulent flow under the influence of a weak inhomogeneous large-scale disturbance. We have shown that turbulent energy redistribution in the presence of nonzero helicity occurs mainly over large scales. Helicity increases correlation time, leading to the weakening of a direct cascade and to the formation of steep spectra over small scales, with simultaneous turbulent energy growth over large scales. Furthermore, an expression for the effective viscosity of the mean flow is derived. It is shown that the magnetic field, in addition to the helicity, reduces the effective viscosity of the medium. This may be important in the study of MHD flow around obstacles in the presence of an external magnetic field. Zh. éksp. Teor. Fiz. 114, 171–181 (July 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Investigation of a Hall MHD channel with an ionization-unstable plasma of inert gases

We investigate a promising scheme for using ionization-unstable plasmas of pure inert gases as the working medium for a magnetohydrodynamic (MHD) closed-cycle generator. Our experiments were carried out using a disc Hall MHD channel, with the flux of ionized gas created in a shock tube. Our working gas was xenon. In these experiments we measured the gas pressure, the flow velocity, the concentration and temperature of the electrons, the azimuthal current density, the distribution of potential in the channel, and the value of the near-electrode voltage drop. We recorded voltage-current characteristics for various values of magnetic field and load resistances. The results of these experiment showed that in an ionization-unstable plasma of inert gases without admixtures of alkali metal, the effective conductivity in the Hall channel increases significantly with increasing degree of criticality of the magnetic field, and the value of the maximum specific power extracted increases more rapidly than the specific power calculated by assuming “frozen” ionization. Zh. Tekh. Fiz. 67, 6–11 (December 1997)     

Some spherical solutions of ideal magnetohydrodynamic equations

Abstract

Some spherical solutions of the ideal magnetohydrodynamic (MHD) equations are obtained from the method of the weak transversality method (WTM), which is based on Lie group theory. This analytical method makes use of the symmetry group of the MHD system in situations where the “classical” Lie approach of symmetry reductions is no longer applicable. Also, a brief physical interpretation of these solutions is given.     

Initial Measurements of Plasma Potential in the Core of the MST Reversed Field Pinch with a Heavy Ion Beam Probe

Measurement of the plasma potential in the core of MST marks both the first interior potential measurements in an RFP, as well as the first measurements by a Heavy Ion Beam Probe (HIBP) in an RFP. The HIBP has operated with (20-110) keV sodium beams in plasmas with toroidal currents of (200-480) kA over a wide range of densities and magnetic equilibrium conditions. A positive plasma potential is measured in the core, consistent with the expectation of rapid electron transport by magnetic fluctuations and the formation of an outwardly directed ambipolar radial electric field. Comparison between the radial electric field and plasma flow is underway to determine the extent to which equilibrium flow is governed by E×B. Measurements of potential and density fluctuations are also in progress.Unlike HIBP applications in tokamak plasmas, the beam trajectories in MST (RFP) are both three-dimensional and temporally dynamic with magnetic equilibrium changes associated with sawteeth. This complication offers new opportunity for magnetic measurements via the Heavy Ion Beam Probe (HIBP). The ion orbit trajectories are included in a Grad-Shafranov toroidal equilibrium reconstruction, helping to measure the internal magnetic field and current profiles. Such reconstructions are essential to identifying the beam sample volume locations, and they are vital in MST's mission to suppress MHD tearing modes using current profile control techniques. Measurement of the electric field may be accomplished by combining single point measurements from multiple discharges, or by varying the injection angle of the beam during single discharges.The application of an HIBP on MST has posed challenges resulting in additional diagnostic advances. The requirement to keep ports small to avoid introducing magnetic field perturbations has led to the design and successful implementation of cross-over sweep systems. High levels of ultraviolet radiation are driving alternative methods of sweep plate operation. While, substantial levels of plasma flux into the HIBP diagnostic chambers has led to the use of magnetic plasma suppression.     

Supersonic flow about a body exposed to electric and magnetic fields

The feasibility of using nonmechanical (electrogasdynamic, EGD, and magnetohydrodynamic, MHD) methods to control shock-wave configurations emerging in supersonic flows is investigated. In the EGD method, the flow is heated by a gas discharge; in the MHD one, the flow is influenced by a Lorentz force arising in a gas discharge upon applying a magnetic field. The influence of the gas discharge and MHD interaction on the position of a detached shock wave appearing in a supersonic xenon flow about a semicylindrical body is studied. A discharge is initiated in the immediate vicinity of the leading edge of the body, and the variation of the shock wave position with the intensity of the discharge (discharge current density) is traced when the influence of the EGD action increases and/or an external magnetic field is applied (the influence of the MHD action increases). Preliminary data for a supersonic air flow about a body are presented.     

FCI结构及其电导率对MHD效应影响实验研究

实验研究了通道插件(FCI)压力平衡孔(PEH)和压力平衡狭缝(PES)结构、绝缘和非绝缘材质对磁流体动力学(MHD)效应的影响,结果表明：带PEH或PES、绝缘或非绝缘材质的FCI产生的流速分布有很大的差异;对MHD压降而言,FCI结构PEHs或PES差异的影响大于FCI绝缘或非绝缘材质差异引起的影响;对流速分布而则刚好相反。二次流引起的局部流速骤增的MHD效应(简称为S-MHD效应)对控制管道内流速分布和降低MHD压降有作用,这些实验结果为弄清FCI的MHD效应机制和液态金属包层设计提供了实验认知与有价值的参考。     

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实验研究了通道插件(FCI)压力平衡孔(PEH)和压力平衡狭缝(PES)结构、绝缘和非绝缘材质对磁流体动力学(MHD)效应的影响,结果表明：带PEH或PES、绝缘或非绝缘材质的FCI产生的流速分布有很大的差异;对MHD压降而言,FCI结构PEHs或PES差异的影响大于FCI绝缘或非绝缘材质差异引起的影响;对流速分布而则刚好相反。二次流引起的局部流速骤增的MHD效应(简称为S-MHD效应)对控制管道内流速分布和降低MHD压降有作用,这些实验结果为弄清FCI的MHD效应机制和液态金属包层设计提供了实验认知与有价值的参考。     

Fractional Green–Naghdi theory for thermoelectric MHD

ABSTRACT

In this work, we use the Green–Naghdi theory of thermomechanics of continua to derive a linear theory of MHD thermoelectric fluid with fractional order of heat transfer. This theory permits propagation of thermal waves at finite speed. The one-dimensional model of the theory is applied to Stokes’ flow of unsteady incompressible fluid due to a moving flat plate in the presence of both heat sources and a transverse magnetic field. The problem was solved using the Laplace transform technique. The solution in the transformed domain is obtained by a direct approach. A numerical method based on a Fourier-series expansion is used for the inversion process. The thermoelectric effects with fractional parameter on the temperature and velocity fields are analyzed and discussed in detail with the aid of graphical illustrations.     

Engines and exhaust after treatment systems for future automotive applications

Engine concepts for future automotive applicationsSafe, clean and efficient engines will become more important in modern societies where we will see higher levels of mobility on one hand and limited resources on the other hand. Gasoline engines for passenger cars have been developed to generate more power and reduce emissions at the same time. Therefore the engine systems have become complex with a number of subsystems.Because of its reliability and efficiency the diesel engine is classically operated in heavy duty vehicles, however in recent years because of its high torque when used with a turbocharger it has become more popular for passenger cars and even sport vehicles as well. The development of the diesel engine especially the direct injection as well as the common rail high pressure injection brought further improvement regarding power, efficiency and emissions. In the future exhaust after treatment systems will be developed in order to comply with emission standards similar to those of gasoline engines.Emission control systems with chemical and physical sensorsIn order to meet the more and more stringent emission regulations gasoline as well as diesel engines will need continuously improved exhaust after treatment systems. The options for the various applications are highlighted in the following.Today exhaust gas of gasoline engines is typically treated with “Three Way Catalysts” (TWC). The catalyst converts the pollutants CO, NO_X and Hydrocarbons into harmless compounds like CO₂, H₂O and N₂ by chemical reactions. Lambda-Sensors control the air fuel ratio of the engine and catalyst performance in order to get the best possible conversion of the pollutants.Modern lean burn engines have other options. Here the pollutants in the exhaust gases are only partially converted by a TWC function i.e. CO and Hydrocarbons. For the remaining NO_X a so called NO_X Storage Catalyst (NSC) is employed, which chemically stores NO and NO₂ during lean burn phase. For the conversion of stored NO_X the engine is periodically shifted to fuel rich operation. This more complex system is controlled with the help of mathematical catalyst models and by Lambda-, Temperature- and optionally NO_X-Sensors as well.Diesel engine exhaust of heavy duty vehicles will be treated with ammonia by Selective Catalytic Reduction (SCR) to reduce NO_X additionally to the catalytic oxidation of CO and Hydrocarbons. The ammonia is generated on board of the vehicle using harmless precursors like for example urea. For the control of this system Lambda-, Temperature- NO_X- and optionally NH₃-Sensors are employed.In addition to gaseous pollutants the particulate emissions from diesel engines will be removed by Diesel Particulate Filters (DPF). The system of oxidation catalyst and DPF is controlled by Temperature-, Pressure- and Particulate-Sensors.The mentioned highlights show that all three goals safe, clean and efficient can be met in the future by both gasoline and diesel engines combined with modern exhaust after treatment systems.     

聚变堆液态包层准二维磁流体湍流模型研究

为研究聚变堆氚增殖包层中液态金属湍流磁流体动力学(MHD)效应,开发了一种新的准二维单方程 MHD 湍流模型,并进行了相关数值模拟程序的编制及验证。对于矩形管道中的准二维 MHD 湍流流动,三维流 动主要发生在哈德曼层中,中心的主流区呈现出二维流动。为了反映这种特殊的流动特征,新湍流模型在标准 k-ε 模型的基础之上去掉了传统的耗散项,代之以电磁耗散项来模拟湍流 MHD 效应。同时,采用 Bradshaw 假设来对 湍流涡粘系数进行模化。为验证该湍流模型是否合理,编制了相关数值模拟程序,并利用直接数值模拟(DNS)结 果对该程序进行了校正,数值模拟结果与 DNS 结果吻合较好。计算结果表明,该湍流模型可应用于聚变堆液态 包层 MHD 湍流流动的数值模拟。     

Self-adjusting,positivity preserving high order schemes for hydrodynamics and magnetohydrodynamics

Several computational problems in science and engineering are stringent enough that maintaining positivity of density and pressure can become a problem. We build on the realization that positivity can be lost within a zone when reconstruction is carried out in the zone. We present a multidimensional, self-adjusting strategy for enforcing the positivity of density and pressure in hydrodynamic and magnetohydrodynamic (MHD) simulations. The MHD case has never been addressed before, and the hydrodynamic case has never been presented in quite the same way as done here. The method examines the local flow to identify regions with strong shocks. The permitted range of densities and pressures is also obtained at each zone by examining neighboring zones. The range is expanded if the solution is free of strong shocks in order to accommodate higher order non-oscillatory reconstructions. The density and pressure are then brought into the permitted range. The method has also been extended to MHD. It is very efficient and should extend to discontinuous Galerkin methods as well as flows on unstructured meshes.Media player

Hall effect on Hartmann flow and heat transfer of a Burgers' fluid

The effect of Hall current on the steady magnetohydrodynamics (MHD) flow of an electrically conducting, incompressible Burgers' fluid between two parallel electrically insulating infinite planes is studied. The MHD flow is generated by applying constant pressure gradient. An external uniform magnetic field normal to the disks is applied. The disks are kept at two different constant temperatures. Exact solutions are obtained for the governing momentum and energy equations. The effects of Hartmann number M, Reynolds number Re, Prandtl number Pr, Eckert number Ec, pressure gradient dp/dx and Hall parameter η are examined.     

Solar-assisted liquid metal MHD power generation: A state of the art study

The research and development of LMMHD energy conversion (EC) systems which started in the 1960s has already come a long way and is heading towards commercialization. Design and development of such systems has to deal with a number of questions relating to single- and two-phase flows of molten metals, including different patterns of two-phase flow, interphase, phenomena, heat transfer, performance of LMMHD components and compatibility of liquid metals with other fluids and with confinement materials. Liquid metal MHD (LMMHD) power conversion systems proposed many years ago are gaining increasing attention in their various proposed modes, consisting of single-phase or two-phase fluid flow for a wide range of heat sources, e.g. solar energy, waste heat, nuclear energy, etc.Liquid metal MHD (LMMHD) power systems have been recently proposed for direct electrical energy conversion of low grade thermal sources of energy, like solar energy. Solar-powered LMMHD power generation systems are very attractive regarding efficiency and cost per unit of installed power. Theoretical and experimental investigations carried out in the various aspects of these systems are presented. A state of the art review of activities in the solar-powered LMMHD power systems field which have taken place so far is described here.     

Formation of compression shocks in a nonequilibrium plasma flow in a magnetic field

Plasma flow in a linearly widening, ideally sectioned, short-circuited magnetohydrodynamic (MHD) channel is studied. MHD flows are classified into two types: continuous flows and flows with a compressional MHD shock in plasmas that are stable and unstable against the onset of ionization instability. Specific features in the evolution of a stationary compression MHD shock are investigated, and its position as a function of the Stewart number is determined. It is found that, in a plasma flow in which ionization instability develops, a compression MHD shock arises at lower values of the MHD interaction parameter than in a stable plasma flow. An unidentified type of instability of MHD discontinuities is revealed.     

Analytical solution of a system of magnetohydrodynamic equations in a quasi-one-dimensional approximation for the monotonic variation of the flow velocity along a channel

An analytical solution is obtained for the system of magnetohydrodynamic (MHD) equations in a quasi-one-dimensional approximation for flow regimes with a monotonic variation of the velocity along a MHD channel. The problem of optimal choice of the parameters of an MHD generator for the given ratio of the areas of the outlet and inlet MHD channel cross sections is considered using the resultant analytic solution.     

Magnetohydrodynamics of a viscous spherical layer rotating in a strong potential field

An analytic solution is given for classical magnetohydrodynamic (MHD) problem of almost rigid-body rotation of a viscous, conducting spherical layer of liquid in an axisymmetric potential magnetic field. Large-scale flows bounded by rigid spheres are described for the first time in a new approximation. Two problems are solved: (1) in which both spheres are insulators and (2) in which the outer sphere is an insulator and the inner sphere a conductor. Axially symmetric flows and azimuthal magnetic fields are maintained by a slightly faster rotation of the inner sphere. The primary regeneration takes place in the boundary and shear MHD layers. The shear layers, described here for the first time, smooth out the large gradients at the boundaries of the MHD structures encompassed by them. There is essentially no azimuthal magnetic field inside these original structures, which are bounded by potential contours tangent to the spheres. An applied constant magnetic field creates a rigid MHD structure outside an axial cylinder tangent to the inner sphere. Inside the cylinder the rotation is faster and the meridional flux depends on height. A magnetic dipole forms a structure tangent to the outer equator. Outside the structure, the rotation is also rigid-body when both spheres are insulators. When a conducting sphere is present, the liquid rotates differentially everywhere, while near the axis and inside the MHD structure, it rotates even faster than the inner sphere. The last example of a general solution is a quadrupole magnetic field. In this case, two equatorially symmetric MHD structures are formed which rotate together with the inner sphere. Outside the structures, as in the most general case, the rotation is differential, the azimuthal magnetic field falls off as the first power of the applied field, and the meridional flux falls off as the square of the field in the first problem, and as the cube in the second. Zh. éksp. Teor. Fiz. 112, 2056–2078 (December 1997)     

Induced electric current-based formulation in computations of low magnetic Reynolds number magnetohydrodynamic flows

We use the induced electric current as the main electromagnetic variable to compute low magnetic Reynolds number magnetohydrodynamic (MHD) flows. The equation for the induced electric current is derived by taking the curl of the induction equation and using Ampère’s law. Boundary conditions on the induced electric current are derived at the interface between the liquid and the thin conducting wall by considering the current loop closing in the wall and the adjacent liquid. These boundary conditions at the liquid–solid interface include the Robin boundary condition for the wall-normal component of the current and an additional equation for the wall potential to compute the tangential current component. The suggested formulation (denominated j-formulation) is applied to three common types of MHD wall-bounded flows by implementing the finite-difference technique: (i) high Hartmann number fully developed flows in a rectangular duct with conducting walls; (ii) quasi-two-dimensional duct flow in the entry into a magnet; and (iii) flow past a magnetic obstacle. Comparisons have been performed against the traditional formulation based on the induced magnetic field (B-formulation), demonstrating very good agreement.