Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session E2: MagnetohydrodynamicsEnergy
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Chair: John Evans, University of Colorado Room: 402 |
Sunday, November 19, 2017 4:55PM - 5:08PM |
E2.00001: Perturbations of the magnetic induction in a bubbly liquid metal flow. Rafael Guichou, Philippe Tordjeman, Wladimir Bergez, Remi Zamansky, Kevin Paumel The presence of bubbles in liquid metal flow subject to AC magnetic field modifies the distribution of eddy currents in the fluid. This situation is encountered in metallurgy and nuclear industry for Sodium Fast Reactors. We will show that the perturbation of the eddy currents can be measured by an Eddy Current Flowmeter coupled with a lock-in amplifier. The experiments point out that the demodulated signal allows to detect the presence of a single bubble in the flow. The signal is sensitive both to the diameter and the relative position of the bubble. Then, we will present a model of a potential perturbation of the current density caused by a bubble and the distortion of the magnetic field. The eddy current distribution is calculated from the induction equation. This model is derived from a potential flow around a spherical particle. The total vector potential is the sum of the vector potential in the liquid metal flow without bubbles and the perturbated vector potential due to the presence of a bubble. The model is then compared to the experimental measurements realized with the eddy current flow meter for various bubble diameters in galinstan. The very good agreement between model and experiments validates the relevance of the perturbative approach. [Preview Abstract] |
Sunday, November 19, 2017 5:08PM - 5:21PM |
E2.00002: High-order Two-Fluid Plasma Solver for Direct Numerical Simulations of Magnetic Flows with Realistic Transport Phenomena Zhaorui Li, Daniel Livescu The two-fluid plasma equations with full transport terms, including temperature and magnetic field dependent ion and electron viscous stresses and heat fluxes, frictional drag force, and ohmic heating term have been solved by using the sixth-order non-dissipative compact scheme for plasma flows in several different regimes. In order to be able to fully resolve all the dynamically relevant time and length scales while maintaining computational feasibility, the assumptions of infinite speed of light and negligible electron inertia have been made. The accuracy and robustness of this two-fluid plasma solver in handling plasma flows have been tested against a series of canonical problems, such as Alfven-Whistler dispersion relation, electromagnetic plasma shock, magnetic reconnection, etc. For all test cases, grid convergence tests have been conducted to achieve fully resolved results. The roles of heat flux, viscosity, resistivity, Hall and Biermann battery effects, are investigated for the canonical flows studied. [Preview Abstract] |
Sunday, November 19, 2017 5:21PM - 5:34PM |
E2.00003: Voyager observations of magnetic field turbulence in the far heliosheath and in the local interstellar medium. Power spectra from high-resolution data. Daniela Tordella, Federico Fraternale, Michele Iovieno, John D. Richardson Voyager 2 (V2) is in the heliosheath (HS) since the termination shock crossing in Aug 2007, while V1 is in the local interstellar medium (LISM) since Aug 2012. The fundamental processes at the basis of the observed solar wind's disordered fluctuations are still unclear. Open points regard the nature of compressive turbulence within the sectored and unipolar HS in proximity of the heliopause and in the LISM. Possibility that MHD waves give origin to turbulence in the LISM has been recently suggested by Zank, Du & Hunana [APJ 842,2017]. However, addressing these issues is a challenging task because of the data sparsity. We provide the first collection of magnetic field power spectra computed in consecutive periods after 2009 from 48s resolution data in the HS (V1, V2) and in the LISM (V1). A description of the fluctuations evolution with the heliocentric distance is given in terms of spectral decay law and anisotropy. In the HS, our observations are consistent with an anisotropic mainly inertial cascade in the frequency range [$10^{-5},5\cdot10^{-4}$] Hz, with spectral slopes from -1.7 to -1.9. Larger scales may be featured by wavy fluctuations leading to a $f^{-1}$ decay for $f<10^{-5}$ Hz. LISM spectra show a $f^{-1}$ power law in the whole observed range [$10^{-7},10^{-2}$] Hz. [Preview Abstract] |
Sunday, November 19, 2017 5:34PM - 5:47PM |
E2.00004: Global structure transitions in an experimental induction furnace Yuji Tasaka, Vladimir Galindo, Tobias Vogt, Sven Eckert Flows induced by alternating magnetic field (AMF) in a cylindrical vessel filled with liquid metal, alloy of GaInSn, were examined experimentally using ultrasonic Doppler velocimetry (UDV). Measurement lines of UDV arranged vertically set at different radial and azimuthal positions extracted flow structures and their time variations as spatio-temporal velocity maps in the opaque liquid metal layer. At low frequency of AMF, corresponding to shielding parameter $S = \mu_{\mathrm{m}} \sigma \omega R^2 = O(1)$ ($\mu_{\mathrm{m}}$ and $\sigma$ are magnetic permeability and electric conductivity of the test fluid, $\omega$ angular frequency of AMF, and $R$ the radius of cylindrical vessel), two toroidal vortices exist in the fluid layer as the large scale flow structure and have interactions each other. With increasing of $S$ the structure has transition from toroidal vortex pair to four large scale circulations ($S \ge 100$) via transient state, where strong interactions of two vortices are observed ($30 < S < 100 $). Faster vertical stream is observed near the cylinder wall because of ski effect caused by AMF, and the time-averaged velocity of the stream takes maximum around $S = 20$, which is little smaller value of $S$ for the onset of the transient state. [Preview Abstract] |
Sunday, November 19, 2017 5:47PM - 6:00PM |
E2.00005: Reconnections of magnetic and vortex surfaces in magnetohydrodynamic Taylor-Green Flows Jinhua Hao, Yue Yang We investigate the reconnections of magnetic and vortex surfaces in three-dimensional magnetohydrodynamic Taylor-Green (MHD-TG) flows using the magnetic-surface field (MSF) and vortex-surface field (VSF). Both MSF and VSF are Lagrangian-based structure identification methods rooted in Alfven and Helmholtz theorems, whose isosurfaces are magnetic and vortex surfaces consisting of magnetic and vortex lines, respectively. The time and location of magnetic reconnection are quantitatively determined from the characterization of topological changes of magnetic surfaces. Similarly, the vortex reconnection is also quantified. In particular, the influence of the Lorentz force on the motion of vortex surfaces is partly considered as a hypothetical convection of VSFs. Furthermore, we elucidate the relationship between the energy transfer and structural evolution of magnetic and vortex surfaces in MHD-TG flows. [Preview Abstract] |
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