Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session E40: Magnetohydrodynamics: Magnetic Fields |
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Chair: Oleg Zikanov, University of Michigan - Dearborn Room: Portland Ballroom 253-258-254-257 |
Sunday, November 20, 2016 5:37PM - 5:50PM |
E40.00001: Metal pad instabilities in liquid metal batteries Oleg Zikanov Strong variations between the electrical conductivities of electrolyte and metal layers in a liquid metal battery indicate the possibility of `metal pad' instabilities. Deformations of the electrolyte-metal interfaces cause strong perturbations of electric currents, which, hypothetically, can generate Lorentz forces enhancing the deformations. We investigate this possibility using two models: a mechanical analogy and a two-dimensional linearized approximation. It is found that the battery is prone to instabilities of two types. One is similar to the sloshing-wave instability observed in the Hall-H\'{e}roult aluminum reduction cells. Another is new and related to the interactions of current perturbations with the azimuthal magnetic field induced by the base current. [Preview Abstract] |
Sunday, November 20, 2016 5:50PM - 6:03PM |
E40.00002: Resonance of a Metal Drop under the Effect of Amplitude-Modulated High Frequency Magnetic Field Jiahong Guo, Zuosheng Lei, Hongda Zhu, Lijie Zhang The resonance of a sessile and a levitated drop under the effect of high frequency amplitude-modulated magnetic field (AMMF) is investigated experimentally and numerically. It is a new method to excite resonance of a metal drop, which is different from the case in the presence of a low-frequency magnetic field. The transient contour of the drop is obtained in the experiment and the simulation. The numerical results agree with the experimental results fairly well. At a given frequency and magnetic flux density of the high frequency AMMF, the edge deformations of the drop with an azimuthal wave numbers were excited. A stability diagram of the shape oscillation of the drop and its resonance frequency spectrum are obtained by analysis of the experimental and the numerical data. The results show that the resonance of the drop has a typical character of parametric resonance. [Preview Abstract] |
Sunday, November 20, 2016 6:03PM - 6:16PM |
E40.00003: Geometrical shock dynamics of fast magnetohydrodynamic shocks Wouter Mostert, Dale I. Pullin, Ravi Samtaney, Vincent Wheatley We extend the theory of geometrical shock dynamics (GSD, Whitham 1958), to two-dimensional fast magnetohydrodynamic (MHD) shocks moving in the presence of nonuniform magnetic fields of general orientation and strength. The resulting generalized area-Mach number rule is adapted to MHD shocks moving in two spatial dimensions. A partially-spectral numerical scheme developed from that of Schwendeman (1993) is described. This is applied to the stability of plane MHD fast shocks moving into a quiescent medium containing a uniform magnetic field whose field lines are inclined to the plane-shock normal. In particular, we consider the time taken for an initially planar shock subject to an initial perturbed magnetosonic Mach number distribution, to first form shock-shocks. [Preview Abstract] |
Sunday, November 20, 2016 6:16PM - 6:29PM |
E40.00004: Mixed convection in liquid metal flow in a horizontal duct with strong axial magnetic field Xuan Zhang, Oleg Zikanov The work is motivated by design of self-cooled liquid-metal breeder blankets for Tokamak fusion reactors. Thermal convection caused by non-uniform internal heating in a liquid metal flow in a horizontal duct with strong axial magnetic field is analyzed numerically. Axial magnetic field is considered strong enough (the Hartmann number up to 10$^{\mathrm{4}}$ corresponding to typical reactor condition) to suppress the streamwise variation of the flow, so a two-dimensional fully developed flow is studied. Duct walls are assumed to be thermally and electrically insulated. The non-uniform internal heat deposited by captured neutrons is fully diverted by the mean flow. Realistically high Grashof (up to 10$^{\mathrm{11}})$ and Reynolds (up to 10$^{\mathrm{6}})$ numbers are considered. It is found that the state of the flow is strongly affected by the vertical stable stratification developing in response to the streamwise growth of mean temperature. Two flow regimes are identified: the regime with developed transverse convection at moderate Grashof numbers, and the regime, in which convection is suppressed at high Grashof numbers. [Preview Abstract] |
Sunday, November 20, 2016 6:29PM - 6:42PM |
E40.00005: Effects of magnetic and kinetic helicities on the growth of magnetic fields in laminar and turbulent flows by helical-Fourier decomposition Moritz Linkmann, Ganapati Sahoo, Mairi McKay, Arjun Berera, Luca Biferale We perform an analytical and numerical study of incompressible homogeneous conducting fluids by Fourier-helical decomposition of the equations of magnetohydrodynamics (MHD) and a subsequent reduction of the number of degrees of freedom. From the stability properties of the most general subset of interacting velocity and magnetic fields on a closed Fourier triad, we make predictions on the large-scale magnetic-field growth depending on the distribution of magnetic and kinetic helicities among the three wavenumbers. In the kinematic dynamo regime we predict the formation of a large-scale magnetic component with a magnetic helicity of opposite sign with respect to the kinetic helicity, a sort of triadic-by-triad $\alpha$-effect in Fourier space, while in presence of strong small-scale magnetic helicity we predict an inverse cascade of magnetic helicity. We confirm these predictions through a series of Direct Numerical Simulations, either seeding different magnetic helical components in a strongly helical flow (turbulent/laminar) or directly injecting helical magnetic fluctuations at small scales. Our results show that important dynamical features of MHD flows can be predicted from an analytically tractable dynamical system derived directly from the MHD equations. [Preview Abstract] |
Sunday, November 20, 2016 6:42PM - 6:55PM |
E40.00006: Azimuthal swirl in liquid metal electrodes and batteries Rakan Ashour, Douglas Kelley Liquid metal batteries consist of two molten metals with different electronegativity separated by molten salt. In these batteries, critical performance related factors such as the limiting current density are governed by fluid mixing in the positive electrode. In this work we present experimental results of a swirling flow in a layer of molten lead-bismuth alloy driven by electrical current. Using in-situ ultrasound velocimetery, we show that poloidal circulation appears at low current density, whereas azimuthal swirl becomes dominant at higher current density. The presence of thermal gradients produces buoyant forces, which are found to compete with those produced by current injection. Taking the ratio of the characteristic electromagnetic to buoyant flow velocity, we are able to predict the current density at which the flow becomes electromagnetically driven. Scaling arguments are also used to show that swirl is generated through self-interaction between the electrical current in the electrode with its own magnetic field. [Preview Abstract] |
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