Vortex dynamics in the wake of a magnetic obstacle

We present an experimental study about the vortex dynamics in liquid metal flow under the influence of confined non-homogeneous magnetic field, so-called magnetic obstacle. A permanent magnet installed on a moving rail beneath a cell, filled with eutectic alloy GaInSn, moves with constant velocities with the corresponding Reynolds number from \(Re = \text{125 to 2000}\) . The liquid metal flow patterns are recorded using a camera moving with the magnet. Small bubbles, which are a product of hydrochloric acid and GaInSn oxide reaction, illuminate the streamlines which are to be presented here. As the velocity and hence Reynolds number and interaction parameter change, complicated phenomena are visible inside the channel including formation of vortices or their suppression, symmetry breakdown, vortex duplication and vortex shedding. The vast number of instability-related phenomena present in the flow past a magnetic obstacle make it worth investigating. This leads to a better understanding of magnetic obstacle or even turbulence. Since it is impossible to present all the observed phenomena in detail in one paper, here we present only a few illustrative examples to provide an overall view of the phenomena occurring. We conclude with a discussion of the flow instabilities and comparison between the results of our experiments and the theoretical predictions of the reference literature.     

Effect of a longitudinal magnetic field on the excitation of plasma wake waves

The effect of a longitudinal magnetic field on the linear wake fields excited by a relativistic electron bunch in a cold homogeneous plasma is considered. The obtained results prove that the presence of an external magnetic field leads to a dependence of the wake wavelength on the transverse coordinate, to a change in the wave amplitude with increasing distance from the bunch, and to the emergence of anharmonicity. It is found that a strong magnetic field reduces the wave amplitude significantly for narrow bunches and changes the amplitude insignificantly for broad bunches.     

Inverted forerunning and wake of the solitary oscillating abrikosov vortex in a magnetic superconductor

The magnetic structure of a solitary oscillating Abrikosov vortex in a magnetic superconductor is investigated. It is shown that the process of the vortex motion in the presence of the magnetic subsystem substantially modifies the shape of the vortex, with the result that there appears an “inverted forerunning” in front of the vortex and an “inverted wake” behind it that is far from its center.     

Study of the current layer at the boundary between the plasma and a magnetic obstacle in a laboratory experiment

The behavior of the plasma and magnetic and electric fields in the current layer that separates oppositely-directed magnetic fields is studied experimentally. The layer is formed by the interaction of a magnetic dipole with a magnetized plasma flow at Mach numbers lower than 10.     

Blockage effects on viscous fluid flow and heat transfer past a magnetic obstacle in a duct

The effect of lateral walls on fluid flow and heat transfer is investigated when a fluid passes a magnetic obstacle. The blockage ratio β that represents the ratio between the width of external magnet M y and the spanwise width L y is employed to depict the effect. The finite volume method (FVM) based on the PISO algorithm is applied for the blockage ratios of 0.2, 0.3, and 0.4. The results show that the value of Strouhal number St increases as the blockage ratio β increases, and for small β , the variation of St is very small when the interaction parameter and Reynolds number are increasing. Moreover, the cross-stream mixing induced by the magnetic obstacle can enhance the wall-heat transfer and the maximum value of the overall heat transfer increment is about 50.5%.     

Electromagnetic scattering model of the Kelvin wake and turbulent wake by a moving ship

Taking the attenuation character of the Kelvin wake and the limitation of the traditional two-scale method into account, the practical electromagnetic (EM) scattering model of the Kelvin wake is obtained by using a facet-based model; and for a turbulent ship wake, it is produced by dealing with the wave energy loss rate due to turbulence with the width of turbulent wake closely following a moving ship. The volume scattering theory of foam or bubbles, by using the vector radiation transfer equation, is introduced to modify the traditional two-scale method, a special method for the EM scattering of a turbulent wake, which brings the scattering of ship wakes into better agreement with the real situation.     

Structure of a metaphosphate glass by magnetic measurements

We compare the EPR spectra of a glassy material x CuO (1 ? x)Na₂O P₂O₅ with a crystal 0.5 CuO 0.5 Na₂O P₂O₅ of known structure. This gives us a mean of defining the copper atom in its site.     

Radar monitoring of a wake vortex: Electromagnetic reflection of wake turbulence in clear air

This article deals with X-band radar trial campaigns in 2006 and 2007 at Orly Airport, and in June 2008 at Paris-CDG Airport. An X-band Doppler radar has been deployed to assess short range (inferior to 2000 m) wake vortex monitoring capabilities in all weather conditions (dry and wet conditions). Recorded data have been correlated with electromagnetic and fluid mechanical models of wake turbulences for better and more accurate understanding of roll-up radar cross section (RCS) and Doppler signature.     

Structure of the magnetic field perturbations of a low-frequency dipole by a metallic sphere

The potentials of the magnetic field of a low-frequency magnetic dipole reflected by a sphere are analyzed. It is shown that for short ranges between the dipole and the sphere this field can be described by one potential, where the field is equivalent to the field of a system of dipoles and charges.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 73–77, March, 1976.     

Polymer chain elasticity in the presence of a topological obstacle

The theory of high elasticity of polymer networks is developed under the assumption that each subchain is situated near a topological obstacle having the form of an infinite straight line, which cannot be crossed by the subchain. The statistics of a polymer chain in the presence of such an obstacle is considered using the well-known results of Edwards, Prager and Frisch, and Saito and Chen. It is shown that qualitative features of the stress-strain curves under uniaxial extension-compression obtained using the present approach correspond to those known from the experiments. However, quantitatively the deviations from the classical high elasticity theory appear to be too small.     

Visualization of the tip vortices in a wind turbine wake

Abstract  

In the present study, an experimental study was conducted to characterize the formation and the evolution of the helical tip vortices and turbulent flow structures in the wake of a horizontal axis wind turbine model placed in an atmospheric boundary layer wind. A high-resolution particle image velocimetry system was used to make detailed flow field measurements to quantify the time evolution of the helical tip vortices in relation to the position of the rotating turbine blades in order to elucidate the underlying physics associated with turbine power generation and fatigue loads acting on the wind turbines.     

Structure of the magnetic field of the Jovian magnetosphere

We exactly solved the problem of the interaction between the rotating magnetic field of Jupiter and the equatorial plasma disk formed by the gases flowing from the Jovian satellite Io. The disk is shown to expel the Jovian magnetic field in both directions, inward, toward Jupiter, compressing its dipole magnetic field, and outward. Jupiter spins up the disk up to velocities that correspond to nearly constant angular rotation, but with an angular frequency lower than the angular frequency of Jupiter itself. The radial velocity of the plasma in the disk approaches its azimuthal velocity. We determined the power of Jupiter’s rotational energy losses. Part of this energy is transferred to the disk, and the other part goes into heating the Jovian ionosphere. We show that the Pedersen surface conductivity of the Jovian ionosphere must have a lower limit to maintain the electric current that arises in the disk-rotating magnetic field system. This current in the Jovian magnetosphere flows only along the preferential magnetic surfaces that connect the inner and outer edges of the disk to the ionosphere.     

Structure of the intersubband collective excitations in quasi-two-dimensional systems in a magnetic field

The spectrum of intersubband collective spin-and charge-density excitations is calculated for a system of quasi-two-dimensional electrons with ν≤10 (ν is the filling factor) in a magnetic field. The transitions both without changing the Landau level and with its change (Bernstein modes) are considered. All excitations are shown to have a multimode structure, the number of modes being determined by the filling factor. The dispersion and interaction of small-quasimomentum collective excitations are also considered. The possibility of observing the multimode structure is predicted.     

Impact of a high-velocity drop on an obstacle

Processes arising when a high-velocity liquid drop strikes a rigid obstacle or a liquid layer were investigated using numerical simulation. The flow pattern being formed features a complicated interaction of compression shock and expansion waves between each other and with free surfaces, the initiation of a cumulative jet flow, and the formation of cavitation areas. Factors governing the interaction process are analyzed. Obtained results are compared with experimental data.     

Self-similar decay of a momentumless swirling turbulent wake

Numerical simulation of the decay of a momentumless swirling turbulent wake of a body of revolution has been carried out. It has been shown that beginning with the distances of the order of 1000 body diameters, the flow passes to the self-similar regime. Using the results of the numerical analysis of the flow, simplified mathematical models of far wake have been constructed.