Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session A13: Magnetohydrodynamics |
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Chair: Olga Shishkina, Max-Planck Institut Room: 304 |
Saturday, November 23, 2019 3:00PM - 3:13PM |
A13.00001: Inclined turbulent thermal convection in liquid sodium Lukas Zwirner, Ruslan Khalilov, Ilya Kolesnichenko, Andrey Mamykin, Sergey Mandrykin, Alexander Pavlinov, Alexander Shestakov, Andrey Teimurazov, Peter Frick, Olga Shishkina Inclined turbulent thermal convection at large Rayleigh numbers (Ra) in extremely small Prandtl-number (Pr) fluids is studied by measurements and high-resolution numerical simulations. The working fluid is liquid sodium (Pr about 0.0094) and the considered Ra is around $1.5\times 10^7$. The convection cell is a cylinder with equal height and diameter, where one circular surface is heated and another one cooled. For the limiting inclination angle $\beta$, which correspond to Rayleigh-Benard convection ($\beta=0$) and vertical convection ($\beta=\pi/2$), the scaling relations of the mean heat flux (Nusselt number Nu) with Ra are studied. Any inclination of the RBC cell leads to an increase of Nu; the maximal Nu is obtained, however, for a certain intermediate value of $\beta$. For small $\beta$, the large-scale circulation (LSC) exhibits a complex dynamics, with torsion and sloshing modes, which are suppressed for large $\beta$. When the LSC is twisted, the volume-average vertical heat flux is minimal, and it is maximal, when the LSC sloshing brings together the hot and cold streams of the LSC. [Preview Abstract] |
Saturday, November 23, 2019 3:13PM - 3:26PM |
A13.00002: Redescribing of Busse balloon on Rayleigh-B\'{e}nard convection imposed by horizontal magnetic field Yuji Tasaka, Takatoshi Yanagisawa, Takehiro Miyagoshi, Tobias Vogt, Sven Eckert Laboratory experiment of RBC was performed using GaInSn eutectic as a typical low $Pr$ fluid with quasi-uniform horizontal magnetic field to elucidate how the Busse balloon describing stability of 2D rolls is modified by Lorenz force effect. Development of the flow from steady rolls to unsteady state were investigated with decreasing Chandrasekhar number $Q$ in a range, $2.5 \times 10^4 \le Q \le 1.9 \times 10^5$ at fixed $Ra$ numbers, $7.9 \times 10^4 \le Ra \le 1.8 \times 10^5$, by ultrasonic velocity profiling. The velocity profile measurements showed the dynamic morphology of the oscillatory convection, 2D oscillation observed at the onset of oscillations, oscillations of recirculation vortex pairs between the main rolls, and synchronous motion of the main rolls. The measurements also suggested that the oscillation occurs at similar Reynolds numbers $Re \approx 900$ and may be caused by instabilities on the recirculation vortex pair.This finding suggests that the oscillations are essentially different from generally observed traveling waves described as the oscillatory instability considered in the Busse balloon. Power law found on the variation of $Re$ with $Q$ suggested the 2D oscillation is dominated by by relation between side wall Hartmann braking and buoyancy. [Preview Abstract] |
Saturday, November 23, 2019 3:26PM - 3:39PM |
A13.00003: Heat transfer and flow regimes in quasi-static magnetoconvection with a vertical magnetic field Ming Yan, Michael Calkins, Stefano Maffei, Keith Julien, Steven Tobias, Phlippe Marti Numerical simulations of Rayleigh-B\'enard convection with an imposed vertical magnetic field are carried out over a broad range of Rayleigh numbers and magnetic field strengths. Three magnetoconvection regimes are identified: two of the regimes are magnetically-constrained in the sense that a leading-order balance exists between the Lorentz and buoyancy forces, whereas the third regime is characterized by unbalanced dynamics that is similar to non-magnetic convection. Each regime is distinguished by flow morphology, momentum and heat equation balances, and heat transport behavior. One of the magnetically-constrained regimes appears to represent an `ultimate' magnetoconvection regime in the dual limit of asymptotically-large buoyancy forcing and magnetic field strength; this regime is characterized by an interconnected network of anisotropic, spatially-localized fluid columns aligned with the direction of the imposed magnetic field that remain quasi-laminar despite having large flow speeds. Heat transport is controlled primarily by the thermal boundary layer. Empirically, the scaling of the heat transport and flow speeds appear to be independent of the thermal Prandtl number within the magnetically-constrained regimes. [Preview Abstract] |
Saturday, November 23, 2019 3:39PM - 3:52PM |
A13.00004: Response of the Free Surface of an Electrically Conducting Liquid to a Magnetic Field Suresh Murugaiyan, Colin Adams, Bhuvana Srinivasan, Stefano Brizzolara Response of the free surface of an electrically conducting liquid to a magnetic field that varies in space and time, is studied using numerical simulations. A fully implicit finite volume solver is used to solve magnetohydrodynamic equations. The equations are solved using a segregated approach on a collocated grid arrangement where all the variables are stored at the cell centers. The PISO (Pressure-Implicit with Splitting of Operators) algorithm is used to solve the equation of fluid momentum with the Rhie and Chow momentum interpolation technique to overcome oscillations in pressure. The equation of magnetic field evolution is solved in the same manner as the equation of fluid momentum by introducing an artificial pressure term. The method of Volume Of Fluid (VOF) is used to track the interface between the two immiscible fluids. Numerical experiments concerning the effect of high density ratio on a two-fluid magnetohydrodynamic system shall be carried out. [Preview Abstract] |
Saturday, November 23, 2019 3:52PM - 4:05PM |
A13.00005: Instability in Electromagnetically Driven Flow between Concentric Spheres Saul Piedra, Aldo Figueroa, Ivan Rivera The rotational flow continuously driven by electromagnetic forcing of an electrolytic fluid in the gap of concentric spheres set-up is studied experimentally and theoretically. The driving Lorentz force is generated by the interaction of a DC electric current radially injected and the dipolar magnetic field produced by a permanent magnet. Velocity profiles in the equatorial plane were obtained using Particle Image Velocimetry (PIV), whereas the radial velocity component of the flow was recorded with Ultrasonic Doppler Velocimetry (UDV). A full three-dimensional numerical model that takes into account the dipolar magnetic field and the radial dependency of the applied current was developed. The model reproduces the main features of the electromagnetically forced flow. For small injected currents, a quite axisymmetric equatorial recirculation formed mainly by diffusive momentum transport was found. For currents above 200 mA, which corresponds to a Re $>$ 1340, instabilities of the inner boundary layer are observed and the flow becomes three-dimensional and time dependent. [Preview Abstract] |
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