32 research outputs found
Core of the Magnetic Obstacle
Rich recirculation patterns have been recently discovered in the electrically
conducting flow subject to a local external magnetic termed "the magnetic
obstacle" [Phys. Rev. Lett. 98 (2007), 144504]. This paper continues the study
of magnetic obstacles and sheds new light on the core of the magnetic obstacle
that develops between magnetic poles when the intensity of the external field
is very large. A series of both 3D and 2D numerical simulations have been
carried out, through which it is shown that the core of the magnetic obstacle
is streamlined both by the upstream flow and by the induced cross stream
electric currents, like a foreign insulated insertion placed inside the
ordinary hydrodynamic flow. The closed streamlines of the mass flow resemble
contour lines of electric potential, while closed streamlines of the electric
current resemble contour lines of pressure. New recirculation patterns not
reported before are found in the series of 2D simulations. These are composed
of many (even number) vortices aligned along the spanwise line crossing the
magnetic gap. The intensities of these vortices are shown to vanish toward to
the center of the magnetic gap, confirming the general conclusion of 3D
simulations that the core of the magnetic obstacle is frozen. The implications
of these findings for the case of turbulent flow are discussed briefly.Comment: 14 pages, 9 figures, submitted to Journal of Turbulenc
Analytic solutions to determine critical magnetic fields for thermoelectric magnetohydrodynamics in alloy solidification
During alloy solidification, it has been observed that the morphology of microstructures can be altered by applying an external DC magnetic field. This structural change can be attributed to solutal convective transport introduced by thermoelectric magnetohydrodynamics (TEMHD) which drives fluid motion within the inter-dendritic region. Complex numerical models with grid resolutions on the microscopic scale have been constructed to solve the equations governing TEMHD. To complement these computationally intensive numerical models, analytic solutions were sought. Specifically, the analytic solutions presented herein are asymptotic solutions derived for TEMHD under low and high magnetic field intensities. Combination of these asymptotic solutions leads to simple formulae for estimating critical magnetic fields which can be readily evaluated in terms of characteristic lengths of materials that have been identified in experiments as key parameters of critical fields. Indeed, the critical magnetic fields predicted with the asymptotic solutions exhibit magnitudes consistent with those applied in current ongoing experiments where significant changes in microstructure have been observed. The capability to predict accurate results indicates that the analytic solutions described herein are valuable precursors not only for detailed numerical simulations but also for experimental design to study critical magnetic fields in alloy solidification
The Effect of Concurrent Straining on Phase Transformations in NiAl Bronze During the Friction Stir Processing Thermomechanical Cycle
Steady Two-Dimensional Channel Flow of an Incompressible Perfect Fluid with Small Electric Conductivity in the Presence of Nonuniform Magnetic Fields
A numerical model coupling thermoelectricity, magnetohydrodynamics and dendritic growth
The purpose of this paper is to discuss in detail the numerical techniques used to investigate the effects of Thermoelectric Magnetohydrodynamics on dendrtic growth. A numerical model is proposed which couples the growth mechanics, solution to the electric potential, fluid mechanics and the transport of heat and mass. The implementation of the equations, solution techniques and the coupling between each of the various physical phenomena is described. A finite difference sharp interface enthalpy based method is used to solve the evolution of the liquid/solid front. The electric potential becomes the solution to Laplace’s equation, with a boundary condition applied to the interface and a sub meshing technique is applied to improve the accuracy. The problem is also inherently 3-dimensional and it can be shown analytically that classical 2-dimensional approximations lead to stagnation of the flow. Therefore a quasi 3-dimensional approximation is used which effectively allows simulations to be carried out in 2-dimensions, which significantly reduces the computational time required