Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session H10: MHD II |
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Chair: Daniel Lathrop, University of Maryland Room: 313 |
Monday, November 21, 2011 10:30AM - 10:43AM |
H10.00001: Numerical study of laboratory MRI experiment Christophe Gissinger, Jeremy Goodman, Hantao Ji Theoretical studies of the MagnetoRotational Instability (MRI) generally rely on a local description, or computations between axially infinite (or periodic) cylinders. Since laboratory MRI experiments involve finite geometries, it is important to understand the effect of boundaries on the MRI. We investigate numerically the flow of a conducting fluid in a Taylor-Couette flow when an axial magnetic field is applied. To minimize Ekman recirculation due to vertical no-slip boundaries, two rotating rings are used in the vertical endcaps, approximating setup used in the Princeton MRI experiment. Our 3D global simulations show that, in presence of boundaries, the nature of the bifurcation, the saturation and the structure of axisymmetric MRI modes are significantly affected by the resultant recirculation. In addition, large scale non-axisymmetric modes are obtained when the applied field is sufficiently strong. We show that these modes are related to destabilization of a free shear layer created by the conjugate action of the applied field and the rotating rings. Finally, we compare our calculations in cylindrical and spherical geometries to recent experimental results obtained in the Maryland experiment and the Princeton MRI experiment. [Preview Abstract] |
Monday, November 21, 2011 10:43AM - 10:56AM |
H10.00002: Turbulent Magnetized Spherical Couette Flow Matthew Adams, Daniel Zimmerman, Santiago Triana, Daniel Lathrop We present experimental studies of the turbulent flow of a conducting fluid in a spherical shear flow in the presence of a magnetic field. Our experimental apparatus consists of an outer spherical shell concentric with an inner sphere, each of which can be rotated independently. The geometry of the experiment makes these studies applicable to geophysical and astrophysical bodies. Liquid sodium serves as the working fluid, filling the gap between the inner sphere and the shell. By applying an axial magnetic field of varying strength, the influence of the applied field on the fluid flow can be studied. Measurements of the magnetic field around the device are used to extract information about the global fluid flow. We also measure the torque required to drive the inner and outer spheres at their respective rotation rates. For a variety of inner and outer sphere rotation rates, we observe enhanced angular momentum transport as the applied field strength is increased, and we compare this with the observed magnetic field pattern and expected magnetorotational instabilities. [Preview Abstract] |
Monday, November 21, 2011 10:56AM - 11:09AM |
H10.00003: Experimental study of the Lorentz forces on a small magnet generated by a liquid metal flow Christiane Heinicke, Gautam Pulugundla, Andr\'e Thess Liquid metals are hot and aggressive and therefore inaccessible to conventional flow measurement techniques. However, the determination of local and global flow properties of metal melts and electrolytes is of great industrial interest. Lorentz force velocimetry is a contactless measurement technique, based on the use of magnets, that is able to bridge this gap. While recent studies showed the suitability of this technique for global flow quantities, this project aims at reaching local resolution inside turbulent liquid metal flows. We can show, how the Lorentz force generated by the magnetic field inside the liquid metal depends on the distance of the magnet to the duct, and more importantly, on the flow velocity. Numerical analyses have been performed with a good agreement with the experimental results. [Preview Abstract] |
Monday, November 21, 2011 11:09AM - 11:22AM |
H10.00004: Instabilities of thin layers of conducting fluids produced by time dependent magnetic fields Javier Burguete We present the recent results of an experiment where thin layers of conducting fluids are forced by time-dependent magnetic fields perpendicular to their surface. We use as conducting fluid an In-Ga-Sn alloy, immersed in a 5\% hydrocloric acid solution to prevent oxidation. The conducting layers have a circular shape, and are placed inside a set-up that produces the vertical magnetic field. Due to MHD effects, the competition between the Lorentz force and gravity triggers an instability of the free surface. The shape of this surface can adopt many different configurations, with a very rich dynamics, presenting azimuthal wave numbers between 3 and 8 for the explored parameters. The magnetic field evolves harmonically with a frequency up to 10Hz, small enough to not to observe skin depth effects and with a magnitude up to 0.1 T. Different resonant regions have been observed, for narrow windows of the forcing frequency. We have analysed the existence of thresholds for these instabilities, depending on the wave number and experimental parameters. These results are compared with others present in the literature. [Preview Abstract] |
Monday, November 21, 2011 11:22AM - 11:35AM |
H10.00005: LES of transitional duct flows by the non-uniform Lorentz force Hiromichi Kobayashi, Hiroki Shionoya, Yoshihiro Okuno Large-eddy simulation (LES) of turbulent duct flows is carried out in the liquid metal MHD power generator, and the influence of the non-uniform Lorentz force caused by the non-uniform magnetic flux density on the turbulent flows is examined. As increasing the high magnetic flux density, the structures of Reynolds stress align along the orientation of the magnetic flux density, and those structures periodically flowed toward the downstream region like Karman vortex sheets are observed. The stronger magnetic flux density makes the laminarized flow turbulent again. That is confirmed by using spectrum analysis. It is found that a pair of eddy as the secondary flow for the non-MHD duct flow diminishes in the MHD flow. The non-uniform magnetic flux density in the streamwise direction produces the eddy currents that lead to the M-shaped velocity profiles in the plane parallel to the external magnetic field. The velocity profiles are modulated more strongly with the magnetic flux density. [Preview Abstract] |
Monday, November 21, 2011 11:35AM - 11:48AM |
H10.00006: Point dipole as a magnetic obstacle in liquid metal duct flow Saskia Tympel, Thomas Boeck, Dmitry Krasnov, J\"org Schumacher Lorentz force velocimetry is a new contactless technique to measure the velocities of hot and agressive conductiong liquids. The measurement of the Lorentz force on the magnet is highly sensitive to the velocity profile that is influenced by the magnetic field. Thus the knowlegde of the flow transformation and the influence of an inhomogeneous local magnetic field on liquid metal flow is essential for obtaining velocity information from the measured forces. We consider liquid metal flow in a square duct with electrically insulating walls under the influence of a magnetic point dipole using three-dimensional direct numerical simulations with a finite-difference method. The dipole acts as a magnetic obstacle. A wide range of parameters affects the created wake. In this canonical setting, we study the modification of the flow for different Hartmann and Reynolds numbers. We observe a strong dependence of the magnetic obstacle effect and the corresponding Lorentz force on the orientation of the dipole as well as on its position. [Preview Abstract] |
Monday, November 21, 2011 11:48AM - 12:01PM |
H10.00007: ABSTRACT WITHDRAWN |
Monday, November 21, 2011 12:01PM - 12:14PM |
H10.00008: Numerical Study of the Interaction of Turbulent Liquid Metal Flow with an Inhomogeneous Magnetic Field Gautam Pulugundla, Christiane Heinicke, Christian Karcher In this work, we present the numerical analysis of a turbulent liquid metal flow in the inhomogeneous magnetic field of a permanent magnet. The study is motivated by Lorentz Force Velocimetry (LFV), a non-contact technique for flow rate measurement of conducting fluids using complex magnet systems producing non-uniform and localised magnetic fields. As a simplified case, we consider the flow of liquid metal in a straight square duct with electrically insulating walls. For this configuration, numerical simulations are performed by coupling the commercial finite volume solver FLUENT and finite element solver COMSOL Multiphysics. Parametric analyses are performed with different flow Reynolds numbers and magnet positions. Furthermore, the numerical results are validated with experimental studies performed in the liquid metal laboratory at Ilmenau University of Technology. The analyses provide good reference results for the numerical calibration of LFV. [Preview Abstract] |
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