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Volume 89, Nº 7 (2025)
Magnetohydrodynamics
The method of incoherent decomposition in the theory of kinematic dynamo
Resumo
We discussed the incoherent decomposition method, which allows us to describe the intermediate asymptotics of perturbation growth in the theory of kinematic dynamo and the theory of transport of passive scalar. This approach allows to take a fresh look at the nature of dynamo at large Prandtl numbers.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1008-1013
1008-1013
Influence of magnetic field on the spectra of optical effects in magnetic fluids with different aggregative stability
Resumo
The spectra of the effects of birefringence, dichroism and transmission spectra of magnetic fluids with different aggregative stability under the influence of a constant magnetic field were experimentally studied. A change in the complex refractive index of aggregates of magnetite nanoparticles during their growth was discovered. An interpretation of the spectral features of optical anisotropy and light transmission in aggregation-unstable magnetic fluids is proposed.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1014-1020
1014-1020
Non-conservative cascades in MHD turbulence
Resumo
In fully developed turbulence, according to Kolmogorov's hypothesis, an extended range of scales, called the inertial range, exists, in which neither external nor viscous forces play an appreciable role, and all statistical properties are determined by the dissipation rate of kinetic energy. Turbulent flows, in which the influence of external forces on scales corresponding to the inertial interval is of fundamental importance, are common in nature. Then, the usual integrals of motion, such as the energy of velocity pulsations, hydrodynamic helicity, etc. cease to be so and other quadratic quantities that include scale dependence become integrals of motion. At the same time, from the point of view of the usual integrals of motion, cascade processes become non-conservative. In this work, this idea is developed in frame of shell models of MHD-turbulence. The approach introduced allows us to describe some special regimes of cascade processes in MHD-turbulence.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1021-1027
1021-1027
Experimental verification of Couette-Poiseuille flow of a magnetic fluid filling coaxial gap between the inner magnetic and external nonmagnetic walls
Resumo
The viscous friction of a coaxial layer of magnetic fluid between the inner wall of a nonmagnetic tube and a cylindrical assembly of permanent magnets during translational motion of the latter has been experimentally investigated. A comparison of the results of friction coefficient measurements with calculations within the framework of analytical models is carried out. It is shown that the model prohibiting the flow of a magnetic fluid from the gap gives the best estimate of the friction coefficient. In several series of experiments on laboratory layouts differing in geometrical dimensions and aspect ratio of magnetic bodies, experimental data confirming the type of Cuette-Poiseuille hydrodynamic flow in the system under study have been accumulated.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1028-1036
1028-1036
Correlation analysis of the interaction of surface magneto-hydrodynamic waves
Resumo
The correlation analysis of the interaction of nonlinear waves on the surface of a magnetic fluid in the regime of developed magneto-hydrodynamic wave turbulence is carried out. It is shown that the horizontal magnetic field leads to compression of the resonant interaction curve. From the physical point of view, this process corresponds to anisotropic transfer of magnetic energy into the energy of capillary waves traveling perpendicular to the external field direction.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1037-1042
1037-1042
Formation of near-surface toroidal magnetic fields of the Sun. Extended solar cycle
Resumo
Observational aspects of the formation of near-surface toroidal magnetic fields on the Sun are considered. Based on the analysis of magnetic field observations in the period 2010–2024, diagrams of the distribution of horizontal magnetic fields and magnetic bipoles of ephemeral regions in the solar cycle are obtained. The obtained diagrams are close to the concept of an extended cycle of solar activity. The formation of surface azimuthal magnetic fields is modeled based on the evolution of U-shaped magnetic bipoles of active regions. Taking into account near-equatorial bipoles with a magnetic field propagating through the solar equator in the modeling made it possible to achieve good agreement with the duration of the azimuthal field polarity at low latitudes.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1043-1049
1043-1049
Features of the temperature dependence of the deformation processes of microdroplets of magneto-sensitive emulsion in constant and alternating magnetic fields
Resumo
We investigated the features of deformation of microemulsion droplets with low interfacial tension at the droplet-medium interface under the influence of magnetic fields in a wide temperature range. The nature of the temperature dependence of the microdroplet deformation parameter on the intensity of both constant and alternating magnetic fields has been established. Differences in the deformation patterns of microdroplets obtained from magnetic fluids with different structural states have been revealed.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1050-1058
1050-1058
Dynamics of a chain of interacting magnetic particles in a one-dimensional periodic energy landscape
Resumo
We explore the dynamics of a one-dimensional chain of paramagnetic colloidal particles in a periodic potential. The model accounts for a constant external force, along with magnetic dipolar attraction and hard-core repulsive interactions between particles. Numerical simulations reveal the emergence of a traveling kink – a chain defect propagating along the chain. We show that the kink emerges beyond a critical force threshold and identify parameter regimes corresponding to distinct dynamic modes such as a pinned kink, a running kink, a cluster kink, and chain drift.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1059-1065
1059-1065
The influence of the magnetic field on photo-induced thermocapillary deformation of the surface of a magnetic fluid layer
Resumo
We studied the features of the photo-thermocapillary effect in magnetic colloids. The effect of the magnetic field on the manifestation of the effect in such media was studied, the features of changing the size and shape of the thermocapillary response depending on the dimensional parameters of the cell with the sample were established. A conclusion is made about the possibility of successful control of the effect using a magnetic field.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1066-1071
1066-1071
Comparative analysis of experimental methods for measuring the magnetoviscous effect
Resumo
We presented the study of magnetic fluid viscosity using a capillary viscometer of our own design and the method of oscillating volume of magnetic fluid in a magnetic field. Samples were studied on various carrier liquids: kerosene and polyethylsiloxane, with a volume concentration of the solid phase φ from 19 to 2.5%. The developed installation based on a capillary viscometer allows viscosity measurements in the magnetic field strength range from 20 to 350 kA/m. Measurements based on system oscillations occur in the range from 150 to 900 kA/m. It was experimentally established that the results obtained using these methods are consistent with each other, which allows us to conclude that both methods provide an identical estimate of the viscosity of a magnetic fluid in a magnetic field.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1072-1077
1072-1077
Magnetic field structures generated by accretion disc dynamo
Resumo
Magnetic fields play an important role in the structure and evolution of accretion disks. There are strong arguments related to the action of the dynamo mechanism. The structure of the magnetic field that can be obtained using various approximations is discussed. Particular attention is paid to the possibility of the emergence of essentially non-axisymmetric solutions.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1078-1083
1078-1083
Investigation of the controlled motion of a magnetically active object in a viscous liquid
Resumo
We studied the motion of a magnetically active object in a channel filled with a viscous liquid under the influence of a magnetic field from a permanent magnet that implements a given mode of movement. A mathematical model of this process and the results of numerical and field experiments for different parameters of object displacement are presented.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1084-1090
1084-1090
The role of magnetorotation instability in the occurrence of magnetic field on the periphery of the galactic disk
Resumo
The occurrence of the magnetic fields of galaxies is usually explained by the action of the dynamo mechanism. Nevertheless, at distances of the order of 15-20 kpc, the action of the dynamo is significantly weakened. The magnetic field in these regions can be described by other mechanisms, for example, magnetorotational instability. In this work, solutions that correspond to both the mechanisms of dynamo and magnetorotational instability have been found.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1091-1096
1091-1096
Vortex flow of electrolytes caused by the interaction of electric current and magnetic field in a cylindrical cell
Resumo
When an external magnetic field interacts with an electric current in a conducting medium, vortex flows can occur. We consider a rotating flow in an external magnetic field at a cylindrical volume, when one of the electrodes is the bottom of the vessel, and the second electrode has small dimensions and is immersed in a conducting liquid from above. Both theoretical and experimental results were obtained: the dependence of the velocity on the radius of the upper electrode was obtained, a solution for the potential and velocity, as well as its senior mode, was analytically found.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1097-1102
1097-1102
Numerical study of the effect of the electrical conductivity of the pipe wall on the flow of a salt melt simulator during an upward flow in a transverse magnetic field
Resumo
We presented the results of a numerical study of the flow of an electrically conductive fluid under the influence of a transverse magnetic field, considering the varying electrical conductivity of the wall of a round pipe measuring 40×2 mm2. The fluid under investigation is a simulated salt melt (a 20% aqueous solution of potassium hydroxide), whose concentration allows for achieving the maximum value of the Hartmann number.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1103-1108
1103-1108
Unsteady fluctuations of a liquid metal flow in a closed volume inside an alternating magnetic field
Resumo
An experimental and numerical study is performed on the fluctuations of a liquid metal flow under the action of electromagnetic forces in a closed volume. The flow is unsteady in the range of considered dimensionless parameters. The region of a solenoid exhibits the most pronounced velocity fluctuations. The amplitude and range of the fluctuations grow along with the Hartmann number.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1109–1114
1109–1114
Laboratory and numerical modeling of the structure of shock waves of young stars' jets
Resumo
The use of Z-pinch facilities makes it possible to carry out well-controlled and diagnosable laboratory experiments to study laboratory jets having scaling parameters close to those of jets of young stars. It was found that a low-concentration region is formed after the first supersonic ejection, allowing subsequent ejections to propagate collimated. An exact solution of the generalized Grad-Shafranov equation for axisymmetric plasma flows was also obtained and the interaction of the plasma ejection with the gas was numerically modelled, which agrees well with the experimental data.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1115-1122
1115-1122
Characteristics of a liquid metal flow generated by a travelling magnetic field in a hollow cylindrical channel and a channel with a coaxial insert
Resumo
The velocities of liquid metal and the processes of formation of the reversal vortex in different flow regimes in a hollow cylindrical channel and a cylindrical channel with an insert are compared. Velocity profiles and pressure drop – flow rate characteristic are obtained. It is shown that with the same intensity of electromagnetic force in the channel with an insert, the metal velocity and flow rate are higher than in the cylindrical channel due a to decrease the reversal vortex contribution.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1123-1129
1123-1129
Induction sensor for control of boundary position and medium electrical conductivity
Resumo
We presented an induction sensor for controlling the boundary and conductivity of the medium. A refined mathematical model of the device is given. The dependencies of the sensor signal on the distance to the electrically conductive cylinder and on the position of its upper boundary are obtained experimentally and numerically. The behaviour of the system response on media with different electrical conductivity: copper, duralumin, stainless steel and lead-tin cylinders with different mass fraction of copper powder is studied.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1130-1137
1130-1137
On the simplest solutions for the total magnetic energy in the convective zone of the Sun and the Earth
Resumo
Based on estimates of the characteristic values of the terms in the hydromagnetic dynamo equations, it is shown that for both planetary-type dynamo and solar dynamo, the stabilizing nonlinearity inversely proportional to the electric current value is significant. Using the average value obtained for it, the simplest hydromagnetic model for magnetic energy is constructed, consisting of one non-homogeneous linear ordinary differential equation.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1138-1142
1138-1142
Comparison of the single-step and multistep approaches to prediction of the solar activity index
Resumo
We compared three different approaches for forecasting a time series of the solar activity index: iterations of a single-step model, an independent single-step forecast for each subsequent month, and a single multi-step forecast for the entire period. In each approach we use a neural network model as the forecasting model with the aid of a theoretical series of solutions obtained from the physical model.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1143-1148
1143-1148
Synchronization effect in a nonlinear solar dynamo model
Resumo
We studied the properties of the main solar activity cycle. Using observational data, one can show a significant synchronization of the dynamo process with a strictly periodic process. The results of numerical simulations show that synchronization of the dynamo wave with the periodic part of the alpha effect can arise in a significant nonlinear dynamo model.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1149-1153
1149-1153
Interaction of multi-directional rotating MHD flow of liquid metal in a cylindrical channel
Resumo
The stability of the mixing layer in a cylindrical cell between two counter-rotating vortex flows created by electromagnetic forces is numerically investigated. The flow is shown in the process of instability development. The resulting Kelvin–Helmholtz instability becomes a source of small disturbances and leads to turbulent mixing of the liquid. The second and third flow modes make the greatest contribution to the development of disturbances.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1154-1160
1154-1160
Surface deformation effect in In-Ga-Sn liquid metal system with hemispherical electrodes
Resumo
A system with a eutectic In-Ga-Sn alloy between hemispherical electrodes is considered. The deformation of the surface of a liquid conductor under the action of an electromagnetic force is investigated. Experimental and calculated values of the current at which the liquid is torn off and a discharge occurs are presented depending on the diameter of the small electrode.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1161-1166
1161-1166
Heat transfer of liquid metal in the heat exchange system "pipe in the channel" in relation to the blanket module of a thermonuclear reactor
Resumo
A complex of computational and experimental studies of liquid metal flows in a combined pipe-in-channel system with double cooling in a transverse magnetic field and without it has been performed. The results of numerical simulation are compared with the experiment. The configuration of the flow and its structure significantly depends on the presence of a transverse magnetic field, as well as on the connection of a natural circulation loop and its cooling.
Bulletin of the Russian Academy of Sciences: Physics. 2025;89(7):1167-1174
1167-1174