Spin-up of a magnetically driven tornado-like vortex

2013 ◽  
Vol 736 ◽  
pp. 641-662 ◽  
Author(s):  
Tobias Vogt ◽  
Ilmārs Grants ◽  
Sven Eckert ◽  
Gunter Gerbeth
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Driving Forces ◽  
Axisymmetric Flow ◽  
Rotating Magnetic Field ◽  
Turbulent Vortex ◽  
Force Magnitude ◽  
Order Of Magnitude ◽  
Converging Flow ◽  
Concentration Condition

AbstractThe spin-up of a concentrated vortex in a liquid metal cylinder with a free surface is considered experimentally and numerically. The vortex is driven by two flow-independent magnetic body forces. A continuously applied rotating magnetic field provides the source of the angular momentum. A pulse of about one order of magnitude stronger travelling magnetic field drives a converging flow that temporarily focuses this angular momentum towards the axis of the container. A highly concentrated vortex forms that produces a funnel-shaped surface depression. We explore experimentally the duration, the depth and the conditions of formation of this funnel. Additionally, we measure the axial velocity and calculate the axisymmetric flow field of this transient vortex at a lower force magnitude. The spin-up vortex is similar to the corresponding developed time-averaged turbulent vortex driven by the same magnetic forces (Grants et al., J. Fluid Mech., vol. 616, 2008, pp. 135–152). There are two main differences. First, the maximum swirl concentration condition cannot be expressed as a constant ratio of the two driving forces. Second, a much higher degree of swirl concentration is feasible. We explain these differences as due to a much lower turbulence during the spin-up.

scholarly journals Power and Momentum Relations in Rotating Magnetic Field Current Drive

1984 ◽  
Vol 37 (5) ◽  
pp. 509 ◽  
Author(s):  
WN Hugrass
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Magnetic Fields ◽  
Phase Velocity ◽  
Current Drive ◽  
Rotating Magnetic Field ◽  
Plasma Current ◽  
Rotating Magnetic Fields ◽  
Frequency Source ◽  
Rotating Field

The use of rotating magnetic fields (RMF) to drive steady currents in plasmas involves a transfer of energy and angular momentum from the radio frequency source feeding the rotating field coils to the plasma. The. power-torque relationships in RMF systems are discussed and the analogy between RMF current drive and the polyphase induction motor is explained. The general relationship between the energy and angular momentum transfer is utilized to calculate the efficiency of the RMF plasma current drive. It is found that relatively high efficiencies can be achieved in RMF current drive because of the low phase velocity and small slip between the rotating field and the electron fluid.

The role of magnetic fields in the early stages of star formation

2018 ◽  
Vol 14 (A30) ◽  
pp. 113-114
Author(s):  
Maud Galametz ◽  
Anaëlle Maury ◽  
Valeska Valdivia
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Magnetic Fields ◽  
Large Scale ◽  
Polarized Emission ◽  
Order Of Magnitude ◽  
Low Mass ◽  
Geometrical Effects ◽  
The Magnetic Field

AbstractMagnetic fields are believed to redistribute part of the angular momentum during the collapse and could explain the order-of-magnitude difference between the angular momentum observed in protostellar envelopes and that of a typical main sequence star. The Class 0 phase is the main accretion phase during which most of the final stellar material is collected on the central embryo. To study the structure of the magnetic fields on 50-2000 au scales during that key stage, we acquired SMA polarization observations (870μm) of 12 low-mass Class 0 protostars. In spite of their low luminosity, we detect dust polarized emission in all of them. We observe depolarization effects toward high-density regions potentially due to variations in alignment efficiency or in the dust itself or geometrical effects. By comparing the misalignment between the magnetic field and the outflow orientation, we show that the B is either aligned or perpendicular to the outflow direction. We observe a coincidence between the misalignment and the presence of large perpendicular velocity gradients and fragmentation in the protostar (Galametz et al. 2018). Our team is using MHD simulations combined with the radiative transfer code POLARIS to produce synthetic maps of the polarized emission. This work is helping us understand how the magnetic field varies from the large-scale to the small-scales, quantify beam-averaging biases and study the variations of the polarization angles as a function of wavelength or the assumption made on the grain alignment (see poster by Valdivia).

scholarly journals MATHEMATICAL MODEL TO CALCULATE THE TRAJECTORIES OF ELECTROMAGNETIC MILL OPERATING ELEMENTS

2021 ◽  
Vol 2021 (2) ◽  
pp. 26-34
Author(s):  
O. Makarchuk ◽  
◽  
D. Calus ◽  
V. Moroz ◽  
◽  
...  
Keyword(s):  
Magnetic Field ◽  
Mathematical Model ◽  
Driving Forces ◽  
Fem Analysis ◽  
Plane Motion ◽  
Rotating Magnetic Field ◽  
Hydrodynamic Resistance ◽  
Design Parameters ◽  
Two Dimensional ◽  
Working Chamber

The purpose of the research under consideration is to develop a mathematical model to calculate the trajectories of the ferromagnetic operating elements (millstones) of an electromagnetic mill, moving in a rotating magnetic field under electrodynamic and hydrodynamic resistance forces being limited by the space of the mill’s working chamber. The millstone motion is described through the equations of plane motion of arbitrary-shaped two-dimensional body. The driving forces of this motion are determined on the basis of the approximation of the tabulated functions connecting the module and the orientation of the equivalent force applied to the millstone, with its position in the working chamber and composite MMF phase of mill inductor winding. These tabulated functions are derived from the estimation of the magnetic field inside a working chamber with millstones, in two-dimensional quasi-stationary approximation, using FEM analysis. The publication contains the approximation algorithm for these tabulated vector functions of a vector argument, mathematical statement of millstones trajectories calculating, and analysis of mathematical experiments results that make it possible to evaluate the adequacy of the model. The developed tool enables conducting quantitative analysis of grinding/mixing process and will help to establish relationships between the electromagnetic mill design parameters and its performance. References 21, figures 6.

Swirling recirculating flow an a liquid-metal column generated by a rotating magnetic field

1987 ◽  
Vol 185 ◽  
pp. 67-106 ◽  
Author(s):  
P. A. Davidson ◽  
J. C. R. Hunt
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Liquid Metal ◽  
Secondary Flow ◽  
Body Force ◽  
The Body ◽  
Rotating Magnetic Field ◽  
Force Balance ◽  
Centripetal Acceleration ◽  
Axial Variation

In this paper we consider theoretical and experimental aspects of axisymmetric, swirling flow which is generated in a column of liquid metal by a rotating magnetic field. Two cases are discussed, one in which there is no axial variation in the stirring force, and one where the body force is restricted to a relatively short length of the column. The latter case is of considerable practical interest in continuous casting.One-dimensional stirring, where the swirl is independent of z and θ, is well understood. The magnetic body force is balanced by shear, all inertial forces being zero (except for the centripetal acceleration). However, in two-dimensional axisymmetric stirring, the axial variation in swirl drives a strong secondary poloidal flow. The principal local force balance is between the magnetic torque and inertia. The body force spins up the fluid as it passes through the forced region and the secondary flow sweeps this angular momentum into the unforced region. Consequently, the size and distribution of the swirl is controlled by the secondary flow.The role of wall friction is considered and shown to control the length of the recirculating eddy. An approximate solution of the inviscid equations of motion, based on the angular momentum integral, is derived for the flow in the forced region. This is compared with the results of numerical experiments.The analysis predicts that the swirl velocity scales on {B(σ/ρω)½}ωR, has a maximum at the bottom of the driven region, and penetrates an axial distance of the order ℝR away from the forced region. (For turbulent flow the Reynolds number ℝ must be based on an effective eddy viscosity.) All these features were reproduced experimentally.

THE LINEAR NON-IRON INDUCTOR WITH ROTATING MAGNETIC FIELD

2018 ◽  
Vol 2018 (49) ◽  
pp. 39-50
Author(s):  
О. Karlov ◽  
◽  
I. Kondratenko ◽  
R. Kryshchuk ◽  
A. Rashchepkin ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Rotating Magnetic Field
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