Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session J20: Magnetohydrodynamics I |
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Chair: Filipe Brandao, Oak Ridge National Laboratory Room: 250 D |
Sunday, November 24, 2024 5:50PM - 6:03PM |
J20.00001: DNS of turbulent channel flows under magnetic fields Filipe L Brandao, Arpan Sircar, Katarzyna Borowiec, vittorio badalassi The inductionless version of the magnetohydrodynamics is implemented in the Nek5000 spectral code, and it is employed to numerically investigate turbulent channels with friction Reynolds numbers varying from 140 to 1120 under a magnetic field at different Hartmann numbers. The implementation is validated for the Hartmann problem with the Hartmann number up to 100,000. The effects of the Lorentz force on the boundary layers and Reynolds stresses are investigated. The Lorentz force induced from the magnetic field is found to suppress turbulence intensities and Reynolds stresses. An increase in the magnetic field magnitude leads to increase in drag and, consequently, a larger pressure drop. The difference between production and dissipation in the turbulent kinetic energy decreased with increasing Hartmann number at the central region and large-scale structures at this region were reduced. The flow invariants are computed and the changes in flow topology due to the magnetic field are discussed in detail. The DNS results will be used as a code-to-code comparison and for the development of closures models for the high-fidelity code being developed at ORNL called VERTEX. |
Sunday, November 24, 2024 6:03PM - 6:16PM |
J20.00002: Dynamics of convective states and transition to chaos in quasi-static magnetoconvection Shujaut H. Bader, Xiaojue Zhu In this work, the dynamics of flow states in two-dimensional (2D) quasistatic magnetoconvection under the influence of a strong vertical magnetic field are explored. Top and bottom plates are free-slip, isothermal and the lateral boundaries are periodic. The strong imposed magnetic field, characterized by the Chandrasekhar number (Q), is anti-parallel to gravity, and the Prandtl number (Pr) is set to unity. Different initial conditions lead to different final statistically stationary states, characterized by a different number of stable rolls and a different set of global transport properties. Furthermore, the behavior of the system to initial conditions is also observed to be vital for the transition pathway to chaos. At a fixed Q, upon increasing the Rayleigh number (Ra), a specific set of initial conditions is observed to lead to an atypical bifurcation sequence, in which the flow reverts back to the steady/quasi-steady state after going through the phases of quasi-periodicity and weak turbulence, finally leading to chaos after yet another intermediary unsteady state. Consistent with similar observations for non-magnetic plane layer convection, it is shown that this atypical behavior of the transition from quasi-periodic/weakly-turbulent states to a steady state is accompanied by a significant changes in the length scale of the flow and the relative contributions of the Ohmic and viscous dissipation. |
Sunday, November 24, 2024 6:16PM - 6:29PM |
J20.00003: Oscillatory dynamos in rotating plane Couette flow Liam O'Connor, Daniel Lecoanet We model a dynamo process using direct numerical simulation (DNS) of the magnetohydrodynamic (MHD) equations in hydrodynamically-unstable rotating plane Couette flow. We find dynamo states which undergo magnetic cycles. In the first phase of each cycle, the weak magnetic field grows exponentially due to a kinematic dynamo instability of the hydrodynamic state. The instability saturates, causing the velocity to decrease substantially. This weak velocity can no longer sustain the magnetic field, causing the field to decay to small values, completing the cycle. We demonstrate that such cycles can be intermittent or chaotic depending on global parameters such as the aspect ratio, Rossby number, and magnetic Prandtl number. |
Sunday, November 24, 2024 6:29PM - 6:42PM |
J20.00004: Numerical simulations for a fluid flow driven dynamo in a precessing cylinder Andre Giesecke, Mike Wilbert, Jan Simkanin, Frank Stefani A magnetohydrodynamic dynamo process is supposed to take place in the |
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