Kazuyuki Ueno

Implicit Large Eddy Simulation of Two-Dimensional Homogeneous Turbulence Using Weighted Compact Nonlinear Scheme

For the aim of computing compressible turbulent flowfield involving shock waves, an implicit large eddy simulation (LES) code has been developed based on the idea of monotonically integrated LES. We employ the weighted compact nonlinear scheme (WCNS) not only for capturing possible shock waves but also for attaining highly accurate resolution required for implicit LES. In order to show that WCNS is a proper choice for implicit LES, a two-dimensional homogeneous turbulence is first obtained by solving the Navier―Stokes equations for incompressible flow. We compare the inertial range in the computed energy spectrum with that obtained by the direct numerical simulation (DNS) and also those given by the different LES approaches. We then obtain the same homogeneous turbulence by solving the equations for compressible flow. It is shown that the present implicit LES can reproduce the inertial range in the energy spectrum given by DNS fairly well. A truncation of energy spectrum occurs naturally at high wavenumber limit indicating that dissipative effect is included properly in the present approach. A linear stability analysis for WCNS indicates that the third order interpolation determined in the upwind stencil introduces a large amount of numerical viscosity to stabilize the scheme, but the same interpolation makes the scheme weakly unstable for waves satisfying kΔx ≈ 1. This weak instability results in a slight increase in the energy spectrum at high wavenumber limit. In the computed result of homogeneous turbulence, a fair correlation is shown to exist between the locations where the magnitude of ∇ × ω becomes large and where the weighted combination of the third order interpolations in WCNS deviates from the optimum ratio to increase the amount of numerical viscosity. Therefore, the numerical viscosity involved in WCNS becomes large only at the locations where the subgrid-scale viscosity can arise in ordinary LES. This suggests the reason why the present implicit LES code using WCNS can resolve turbulent flow field reasonably well.

Numerical simulation of deformed single bubbles rising in magnetic fluid

Abstract Axisymmetric flow fields containing a rising bubble under a vertical uniform magnetic field are simulated by a front capturing method. In the case of a weak magnetic field, dynamic pressure makes bubbles oblate, while in the case of a strong magnetic field, magnetic pressure makes bubbles prolate. A map of the shape of bubbles is obtained.

Induction pump for high-temperature molten metals using rotating twisted magnetic field: thrust measurement experiment with solid conductors

We propose a new electromagnetic pump, applicable to high-temperature molten metal in cylindrical ducts. A rotating twisted magnetic field is generated by the stator with three pairs of helical windings. Axial thrust, as well as rotational torque, acts on the secondary conductor. It is verified that the thrust is actually obtained in experiments with a prototype stator and solid secondary conductors (bulk rotors). We discuss the slip-thrust curve for various conductivities of the secondary conductors.

Numerical analysis of unsteady gas–liquid two-phase flow of magnetic fluid

Abstract The basic equations are formulated to analyze an unsteady two-phase flow of magnetic fluid by using a Drift-flux model that is solved numerically. The effect of an applied magnetic field on the two-phase flow characteristics such as distributions of void fraction, pressure and temperature is clarified.

Study on single bubbles rising in magnetic fluid for small Weber number

Abstract Deformation of single bubbles is discussed, taking account of magnetic fluid flow around it. Axisymmetric and steady flows were numerically solved in a vertical uniform magnetic field on the assumption of small deformation. The shapes of the bubbles are determined by normal stress on the interface, and the neutral line for oblate—prolate deformation is obtained.

Induction pump for high-temperature molten metals using rotating twisted magnetic field: molten gallium experiment

We report a study of an electromagnetic pump, applicable to processing high-temperature molten metal such as molten steel at over 1500/spl deg/C. A rotating twisted magnetic field is generated by a stator with three pairs of helical windings. Axial thrust, as well as rotational torque, acts on the molten metal in cylindrical ducts. We carried out a molten metal circulation experiment using molten gallium at 50/spl deg/C and confirmed that the conventional slip-thrust relation is satisfied in the experiment. Here, we identify the slip for each experimental condition and discuss the motion of molten gallium in the rotating twisted magnetic field. The normalized stalling pressure is obtained at the frequency at which /spl delta//a/sub 2//spl ap/0.6, where /spl delta/ is the skin depth and a/sub 2/ is the radius of molten metal.

Hyperfine interactions in europium chalcogenides

Abstract The hyperfine interaction in europium chalcogenides is discussed theoretically. The f–s transfer mechanism explains the nearest neighbour transferred hyperfine interaction. Moreover the p-s and p-f transfer mechanisms explain the next nearest neighbour transferred hyperfine interaction. The estimated values and chalcogen dependences of these are in good agreement with the experiments.

A moment model with variable length scale for the motion of a vortex pair in two-dimensional incompressible flows

A simple model for the motion of a vortex pair in two-dimensional inviscid flows is presented. In this model the motion of the vortex pair is expressed by a set of ordinary differential equations for the dipole moment, the length scale, and the centroid position. The length scale is the distance between the positive vortex and the negative vortex in the pair. A self-propelling velocity of the model vortex pair is introduced in response to a wide range of the length scale. If a background flow is a linear function of the position, the dipole moment and the length scale of the model are exact. This model works well for a separated vortex pair, although it is not applicable to an asymmetrically deformed vortex pair.

Damping rate of magnetohydrodynamic vortices at low magnetic Reynolds number

The damping rate of vortices in an electrically conducting fluid submitted to a uniform magnetic field is analyzed for a large Hartmann number Ha. The fluid is contained in a layer of constant thickness h, bounded by two insulating walls that are perpendicular to the magnetic field. The damping times and the eigenfunctions along the magnetic field are obtained from a linear eigenvalue problem. According to the damping times and these eigenfunctions, vortices are classified into several classes by the range of combinations of the mode number m in the magnetic field direction and the wave number k2D in the plane perpendicular to the magnetic field. It is found that the damping rate of vortices in the range of k2D∼[(m+12)πHa]1∕2h−1 and m=0,1,2 is of the same order as that of large-scale two-dimensional vortices. This fact suggests that actual quasi-two-dimensional magnetohydrodynamic turbulent flows include not only m=0 but also higher-mode (m⩾1) eigenfunctions of this wave-number range, although the eigenfu...

Applications of Low Temperature, AC Superconducting Magnets to Material Processing

Superconducting technology has conventionally been used in magnetic separation using high DC field as its industrial application. In the field of electromagnetic processing of materials (EPM), on the other hand, it has a lot of advantages in the production of high quality, high value-added materials, such as uniformity in crystals, faster refining speed, facilitation of separation of inclusions, and attracts considerable attention. In the present study, we intended to lay a new path to industrial application of superconducting technology, and aimed at applying AC superconducting technology to high AC field as is expected in EPM. We examined thermal insulation technology regarding high temperature metals and low temperature superconducting magnets, and showed a path to solutions. We also designed magnets for applied stirring field, and made a prototype of magnets in which effective countermeasures are adopted against the shape of magnets and electromagnetic oscillation