Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session L8: Magnetohydrodynamics II |
Hide Abstracts |
Chair: Geo A. Richards, National Energy Technology Laboratory Room: 330 |
Monday, November 25, 2013 3:35PM - 3:48PM |
L8.00001: Detecting obstacles in a liquid metal flow with a small permanent magnet Christiane Heinicke, Auni Kundu Flow measurement remains challenging for liquids that are opaque and chemically aggressive. Several contact-free measurement techniques have been developed that rely on the electrical conductivity of the liquid and the resulting interaction of the liquid with external magnetic fields. One of these electromagnetic techniques is the so-called Lorentz Force Velocimetry. Its advantage over other techniques is the possibility to perform measurements with a spatial resolution of the flow field. So far, however, it has remained unclear how deep the influcence of the magnetic field reaches into the liquid. We will present a liquid metal experiment whose flow structure is altered by obstacles at variable distance from the measurement device. From measurements using Lorentz Force Velocimetry we can deduce the position of objects in the liquid metal that are invisible from outside. [Preview Abstract] |
Monday, November 25, 2013 3:48PM - 4:01PM |
L8.00002: Effects of magnetic fields on heat transfer in flowing liquid metals J. Rhoads, E. Edlund, P. Sloboda, H. Ji The presence of a magnetic field can significantly change the dynamics of large and small scale features within conducting fluids. In particular, turbulent eddies with vorticity misaligned with the magnetic field are strongly damped via ohmic dissipation. Studying the anisotropic damping of the turbulence is critically important for understanding heat transport in flowing liquid metals. Experiments have been conducted in the Liquid Metal Experiment (LMX) using a GaInSn eutectic alloy as a working fluid to investigate these effects. These experiments considered free-surface, wide aspect-ratio flows with fluid velocities up to 20 cm/s and a uniform applied magnetic field strength up to 2 kG, corresponding to Reynolds numbers up to $Re \sim 10^4$ and interaction parameters up to $N \sim 10$. Heat was injected into the flow via a resistive heater placed on the free surface and the fluid temperature downstream was monitored by an array of thermocouples and an infrared camera, while an array of velocity probes provided measurements of vortical structures within the flow. The changes observed in both vortical structures and global heat transfer within the fluid will be presented. [Preview Abstract] |
Monday, November 25, 2013 4:01PM - 4:14PM |
L8.00003: An Axisymmetric Hydromagnetic Instability in Spherical-Couette Flow Matthew Adams, Daniel Zimmerman, Santiago Triana, Daniel Lathrop We present experimental studies of the magnetized turbulent shear flow of a conducting fluid in a spherical-Couette device. Our experimental apparatus consists of an outer spherical shell concentric with an inner sphere. The geometry of the experiment makes these studies geophysically and astrophysically relevant. Liquid sodium fills the gap between the inner sphere and the shell, and we apply an axial magnetic field of varying strength. Instrumentation includes an array of hall probes to measure the induced magnetic field, providing 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 the case of corotating spheres with a rotation rate ratio of inner to outer frequency of 8, at high field an axisymmetric instability appears. This instability is anti-correlated with large fluctuations in the torque required to drive the inner sphere, indicating a significant effect on angular momentum transport. We investigate the dependence of the onset of the instability on the rotation rate ratio (or Rossby number), magnetic Reynolds number (characterizing the overall speed of the system), and Lundquist number (characterizing the strength of the applied magnetic field). [Preview Abstract] |
Monday, November 25, 2013 4:14PM - 4:27PM |
L8.00004: Initial observations from the three meter diameter geodynamo experiment Daniel Lathrop, Daniel Zimmerman, Santiago Triana, Henri-Claude Nataf A liquid sodium model of the earth's outer core has been fabricated to be able to reach a magnetic Reynold number of Rm=900. The first two years of experiments were done using water as a working fluid and observed precessionally driven flows and turbulent bi-stability in spherical Couette flow. We now have the initial sodium metal flows in hand with a few months of trial runs. We have seen significant magnetic field induction by the Omega effect and many other induced magnetic field effects. While no dynamo effect has been observed at half speed (Rm $<$ 450) we have seen a gain of seven in the Omega effect, but not yet enough conversion of toroidal to poloidal field to self-generate. We have also characterized the power input of the system as a function of Rossby number, observed a dozen different non-dynamo states, and examined the fluctuations in induced magnetic field. For now, this is at parameters not yet accessible by simulation, but the observations are likely amenable to theory in reduced models. [Preview Abstract] |
Monday, November 25, 2013 4:27PM - 4:40PM |
L8.00005: Non-Darcy Effects in Magnetohydrodynamic Natural Convection in a Cavity Filled with a Porous Medium Amar K C, Abhilash J. Chandy Magnetohydrodynamic (MHD) natural convection in a porous medium has received considerable attention recently, on account of its applicability in many fields of science and engineering like geophysics, chemical processes and material processing. Low-magnetic Reynolds number ($Re_m$) MHD natural convection is investigated in a rectangular cavity with isothermal walls on the left and right and adiabatic walls on the top and bottom. The validity of Darcy's law is addressed for high-Rayleigh number ($Ra$) flows with high permeability, where the velocity-pressure gradient relationship transitions from linear (that is the Darcy law) to nonlinear, due to the fact that the form drag due to solid obstacles is now comparable with the surface drag due to friction, which in turn results in the Darcy-Forchheimer law. In addition, the effect of different magnetic field strengths in terms of Hartmann numbers ($Ha$) is also investigated to analyze how the flow and thermal characteristics in a porous medium are influenced by the applied magnetic field. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700