Bulletin of the American Physical Society
2006 59th Annual Meeting of the APS Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2006; Tampa Bay, Florida
Session LH: Minisymposium IV: Fluid Dynamics and Plasma Physics* |
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Chair: Bhimsen Shivamoggi, University of Central Florida Room: Tampa Marriott Waterside Hotel and Marina Florida Salon 6 |
Tuesday, November 21, 2006 8:00AM - 8:26AM |
LH.00001: Vortex and Current Singularities in Fluids and Plasmas Amitava Bhattacharjee Vortex and current singularities play an important role in reconnection and turbulence phenomena in fluids and plasmas. In this talk, we will review some recent developments on the possible development of such singularities beginning from smooth initial conditions in fluids and plasmas. [Preview Abstract] |
Tuesday, November 21, 2006 8:26AM - 8:52AM |
LH.00002: Structures and nonlocal interactions in fluids and MHD Annick Pouquet, Pablo Mininni, Alexandros Alexakis Direct numerical simulations of three-dimensional Navier-Stokes and magnetohydrodynamic (MHD) turbulence (with grids of up to $1536^3$ points in MHD) are analyzed to study the formation and role of small scale structures and the degree to which nonlinear terms are nonlocal, i.e. involving widely separated scales. A sharp Fourier filter is used, and both decaying and forced flows are studied, with periodic boundary conditions. In the fluid case, roughly 20\% of interactions correspond to the small scales exchanging energy with the forcing scale of the flow, leading to a slow recovery of symmetries in the small scales and giving credence to models involving entrainment by a large-scale flow (Phys. Rev. Lett. {\bf 95}, 264503, 2005). In MHD, the transfer itself has strong non-local components (Phys. Rev. E {\bf 72}, 046301 and 046302, 2005), with the implication that, as soon as one exits the linear phase of exponential growth of small scales in the form of vorticity and current sheets, a plethora of structures form, with a self-similar in time growth of the maxima of current and vorticity $\sim t^3$, with a $k^{-3}$ energy spectrum at those early times and with later, a constant rate of energy dissipation. These results will be illustrated on several flows. We also show that the current and vorticity sheets are spatially co-located and that, at the highest resolution, Kelvin-Helmoltz instabilities develop leading to roll-up of the sheets whereas at lower Reynolds numbers, the sheets simply fold after having been stretched. [Preview Abstract] |
Tuesday, November 21, 2006 8:52AM - 9:18AM |
LH.00003: Collisionless Magnetohydrodynamic Turbulence in Two Dimensions Bhimsen Shivamoggi Collisionless magnetohydrodynamic (MHD) turbulence in two dimensions is discussed [1]. Effects of electron inertia and electron pressure are included. Vortex formation at scales of the order of ion gyro-radius is predicted and compared with recent \textit{in situ} European multi-satellite observations [2]. \newline \underline {References:} \newline [1] B.K.Shivamoggi : \textit{Ann. Phys}. \underline {315},1, (2005). \newline [2] D.Sundkvist et al.: \textit{Nature} \underline {436}, 825, (2005). [Preview Abstract] |
Tuesday, November 21, 2006 9:18AM - 9:44AM |
LH.00004: Magnetofluid computations inside a spherical shell. David C. Montgomery*, Pablo Mininni*, Leaf Turner Magnetohydrodynamic (MHD) dynamo computations have been carried out inside a perfectly conducting spherical shell in the absence of rotation (Mininni and Montgomery, arXiv:physics/0602147). Our emphasis has been on generic dynamo behavior rather than on realistic parameter ranges. The inclusion of a Coriolis force in the equation of motion has been implemented and introduces several new features into the dynamics. Sudden reorientations of the magnetic dipole moment have not been uncommon. The computation is spectral and expands the solenoidal fields of the problem in terms of orthonormal eigenfunctions of the curl. The next step in realism might be the replacement of the conducting shell by an insulating, mechanically impenetrable one. The neglected problem of matching time-varying MHD fields to vacuum electrodynamic fields across such an interface raises unsuspected problems, because of the possibility of radiated electromagnetic energy to infinity. We have been exploring possible remedies, including a version of MHD that does not neglect the displacement current. \newline \newline *Work supported in part by the National Science Foundation. [Preview Abstract] |
Tuesday, November 21, 2006 9:44AM - 10:10AM |
LH.00005: Reverse Dynamo-Flow Generation Swadesh Mahajan The ``reverse dynamo'' mechanism, the amplification/generation of the fast plasma flows by microscale (turbulent) magnetic fields via magneto-fluid coupling is recognized and explored. It is shown that macroscopic magnetic fields and flows are generated simultaneously and proportionately from microscopic fields and flows. The stronger the microscale driver is, the stronger the macroscopic products will be. A detailed calculation based on the double Beltrami driver fields is carried out to illustrate the general features of the system. [Preview Abstract] |
Tuesday, November 21, 2006 10:10AM - 10:36AM |
LH.00006: Entropy conservation in dynamic plasma simulations Joachim Birn, Michael Hesse, Karl Schindler The one-fluid magnetohydrodynamic (MHD) equations are the most common tool in investigating plasma behavior on temporal and spatial scales that are large compared to typical particle scales, such as gyroperiods and gyroradii. One of the frequent assumptions is that of adiabatic, i.e., entropy conserving, transport. In general, non-isotropic, plasmas this assumption may be violated, in addition to the possible break-down of the frozen-in flux approximation of ideal MHD. Here, entropy conservation is investigated for the dynamic field evolution associated with fast magnetic reconnection, based on a comparison between resistive MHD and particle-in-cell (PIC) simulations. Specifically, the entropy and mass integrated along magnetic flux tubes are compared between the simulations. It is shown that there is very good agreement between the conservation of these quantities in the two simulation approaches, despite the effects of dissipation, provided that the resistivity in the MHD simulation is strongly localized. This follows from the fact that dissipation is highly localized in the PIC simulation also, and that slipaage and heat flux across magnetic flux tubes have negligible effect. This result lends support for using the entropy-conserving MHD approach not only before and after reconnection but even as a constraint connecting the two phases. [Preview Abstract] |
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