Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session X30: Magnetohydrodynamics |
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Chair: Douglas Kelley, University of Rochester Room: 154AB |
Tuesday, November 21, 2023 8:00AM - 8:13AM |
X30.00001: Magneto-Stokes Flow in a Shallow Free-Surface Annulus Cy S David, Eric W Hester, Yufan Xu, Jonathan M Aurnou We present a magnetohydrodynamic flow inspired by the remarkable kinematic reversibility of viscous Taylor-Couette flows. We retain the cylindrical-annular geometry of the Taylor-Couette cell, but consider "magneto-Stokes" flow of a shallow, free-surface layer of electrolyte driven by applied electromagnetic forces. An analytical solution is presented here and validated with coupled laboratory and numerical experiments. The dominant balance of Lorentz forcing and basal viscous drag reproduces the kinematic reversibility observed by Taylor with precise electromagnetic control. Induced fluid deformation may be undone by simply reversing the polarity of electric current through the system. We illustrate this analogy with theory and experiment, and we draw a further connection to potential flow using the Hele-Shaw approximation. The stability and controllability of the magneto-Stokes system make it an attractive tool for investigating macro-scale shear flows in a variety of settings from industrial to astrophysical. In addition, the simplicity of the set-up and robustness of the flow also make magneto-Stokes flow a good candidate for PIV calibration and for educational demonstrations of magnetohydrodynamics, boundary layers, and flow transition. |
Tuesday, November 21, 2023 8:13AM - 8:26AM |
X30.00002: Magnetophoresis of transition metal salts through porous media Peter Rassolov, Jamel Ali, Theo Siegrist, Munir Humayun, Hadi Mohammadigoushki Magnetomigration, or the movement of solutes in a solution driven by magnetic field gradients, presents a possible mechanism for emerging chemical process separations technologies, pollutant removal, and drug delivery; however, this phenomenon is still poorly understood. In this work, we investigate the motion of transition metal ions subject to magnetic fields using 2D numerical simulations. A modified version of the Stefan-Maxwell model is numerically solved for a mixture of ions in aqueous solutions and solved simultaneously with the Navier-Stokes and static magnetic field equations. Simulations are performed in a silica gel based porous medium. Using a finite-element model validated against prior published experimental studies, we demonstrate that solutes can overcome their thermal motion and experience net motion towards strong magnetic gradient fields. Additionally, we found that differences in adsorption activity can cause differences in magnetophoresis of different solutes to deviate from predictions based on magnetic susceptibility. |
Tuesday, November 21, 2023 8:26AM - 8:39AM |
X30.00003: Using Radiation from the Wakefield of a Hydromechanically Generated Toroidal Argon Plasma for Electron Parameter Diagnostics Sean Mendoza, Morteza Gharib Toroidal plasmas generated through extreme hydrodynamic shear are a unique instance of atmospheric plasmas that are indefinitely stable without external sources of electric current or potential. The extreme shear created from an impinging water jet creates intense polarization (via triboelectrification) resulting in ionizing discharges into the ambient gas. In this work, optical emissions from this type of toroidal plasmoid in argon are used as the diagnostic medium to measure electron behavior in the plasma. Measurement of spectral lines of argon and continuum radiation emitted from the plasma allow a calculation of a spatial distribution of electron temperature. It is shown that the bremsstrahlung radiation from electron-neutral collisions is the dominant source of continuum radiation. Furthermore, a radial blue-shift of bremsstrahlung radiation is measured, indicating electron acceleration through an electric field. |
Tuesday, November 21, 2023 8:39AM - 8:52AM |
X30.00004: Objective Transport Barriers to the Magnetic Flux and Electromagnetic Energy in Magnetohydrodynamics Alex Pablo P Encinas Bartos, Balint Kaszas, Simon Merkt, George Haller Recent work has identified objective (frame-indifferent) material barriers that inhibit the flux of dynamically active vectorial quantities (i.e. linear momentum and vorticity) in Navier-Stokes flows. In the context of magnetohydrodynamics (MHD), the magnetic field is directly coupled to the evolution of the velocity field through the Lorentz force and therefore qualifies as a dynamically active vector field. Here, we propose to identify material barriers to the transport of active vectorial quantities in MHD such as the electromagnetic energy, i.e. poynting vector. We additionally identify material surfaces that pointwise inhibit the magnetic flux over some time-interval. A general data-driven algorithm is developed for locating objective barriers that minimize the flux of these vectorial quantities. The identified hidden coherent structures highlight important pathways in MHD responsible for the energy transport in the magnetic field. We illustrate the results on three-dimensional homogenous isotropic MHD simulations from the John Hopkins Turbulence Database. The transport barriers resulting from the magnetic field are finally compared to advective and active kinematic barriers. |
Tuesday, November 21, 2023 8:52AM - 9:05AM |
X30.00005: Electrovortex flow in liquid gallium Mohammad Y Abdelshafy, Jonathan S Cheng, Ibrahim A Mohammad, Bitong Wang, Douglas H Kelley Liquid metal batteries are a promising energy storage technology where the electrodes and electrolyte are liquid. The interaction of the current in these batteries with its own magnetic field induces electrovortex flow (EVF) in the conducting fluids. Understanding convection and EVF in these devices and their interactions is crucial: although induced flows can enhance mass transfer, if the flows are fast enough they could disrupt the electrolyte layer and short the battery internally. Therefore, it is important to determine the current ranges at which unfavorable flow occurs. |
Tuesday, November 21, 2023 9:05AM - 9:18AM |
X30.00006: Simulation and validation of MHD benchmark problems using ALMA Pranav Suresh Puthan, Federico D Halpern, Akshay Deshpande, Juan Diego Colmenares, Mark Kostuk High resolution simulations are well known for their predictive capability in liquid metal cooling applications such as liquid metal blankets. ALMA (Anti- symmetric, Large-moment, Accelerated) is a high-performance computational engine designed to solve plasma and neutral gas models on hybrid supercomputers (Halpern et al, 2021). Since the anti-symmetric formulation conserves quadratic invariants of the system (such as energy and enstrophy), the solver is robust, numerically stable and easily scalable while tackling high resolution, multi-variate and unsteady neutral MHD flows. To demonstrate the solver capabilities in liquid metal blanket applications, benchmark problems proposed by Smolentsev et al [2015] are simulated. Firstly, the fully developed flow of a conducting liquid in a rectangular duct subject to uniform transverse magnetic field is considered. Insulating walls and walls of finite conductance are chosen and the flow profile is validated for a range of Hartmann numbers (varying from 500 to 15000). Secondly, the liquid metal flow in square duct subject to a spatially varying magnetic field is chosen. The velocity profile and pressure drop across the duct were validated with the experimental data and analytical expressions. |
Tuesday, November 21, 2023 9:18AM - 9:31AM |
X30.00007: Optimal Design of the Liquid Metal Feeding System for Fusion Reactor Blankets through High-Fidelity MHD Simulations Yuqiao Fan, Sergey Smolentsev PbLi is the liquid metal (LM) used in the fusion reactor blanket for Tritium breeding and blanket cooling. The conventional LM feeding system design involves two separate inlet and outlet pipes, while the advanced design opts for two coaxial pipes to save space. Given that the blanket is subjected to a strong magnetic field within the fusion reactor, the LM flow experiences a significant magnetohydrodynamics (MHD) pressure drop. A well-designed feeding system will reduce this pressure drop and enhance flow uniformity to avoid underfed blanket channels. |
Tuesday, November 21, 2023 9:31AM - 9:44AM |
X30.00008: Numerical Simulation of Free Surface Liquid Metal Flows using FreeMHD for Nuclear Fusion Applications Brian R Wynne, Francisco J Saenz, Jabir Al-Salami, Changhong Hu, Kazuaki Hanada, Egemen Kolemen FreeMHD is an open source magnetohydrodynamics (MHD) solver, recently developed for free-surface liquid metal (LM) flows under strong magnetic fields. The extreme heat fluxes > 10 MW/m^{2} in the divertor region of tokamaks may require an alternative to solid plasma-facing components, for the extraction of heat and the protection of the surrounding walls. However, codes to simulate the behavior of free-surface LM under fusion-relevant conditions are not available. Previous numerical studies have mainly used steady-state, 2D, or simplified models for internal flows and have not been able to adequately model free-surface LM experiments. Therefore, FreeMHD, aims to compute incompressible free-surface flows with multi-region coupling for the investigation of MHD phenomena involving fluid and solid domains. The objectives of the project involve validation and verification of FreeMHD to solve fully 3D transient MHD flows. The model utilizes the electric potential formulation to solve the inductionless MHD equations, implemented using the open-source, finite-volume OpenFOAM framework. FreeMHD is validated using analytical solutions for closed channel flows by examining the effect on the closed channel velocity profile and pressure drop while varying the Hartmann number and wall conductance ratio. Experimental measurements of liquid metal depth and velocity are then used to verify FreeMHD for free-surface LM flow on the Liquid Metal eXperiment Upgrade. |
Tuesday, November 21, 2023 9:44AM - 9:57AM |
X30.00009: Data-driven modeling of MHD turbulence for fusion device blankets Arpan Sircar, Katarzyna Borowiec, Vittorio Badalassi A Large-eddy simulation database of MHD turbulent channel flow with a wall-normal magnetic field has been generated using the open-source tool, OpenFOAM. The Lorentz force in the momentum equation and the Poisson equation for electric potential have been implemented and validated against existing Direct Numerical Simulation results. The range of Reynolds (Re) and Hartmann (Ha) numbers covered are relevant to fusion device blankets. Presently a range of 5,000 < Re < 50,000 and 10 < Ha < 500 is explored relevant to molten salt blanket concepts. This will be extended to higher Ha up to about 10,000 relevant for liquid metals later. The database is used to train machine learning (ML) models for predicting the source terms for the turbulent kinetic energy (k) and turbulence dissipation rate (ε) that can be used for the k-ε Reynolds averaged Navier Stokes model. This model is then exercised in fusion blankets to assess the difference in predictions with and without a turbulence model accounting for MHD effects. Presently, the database and the ML models are being extended to include the effect of three-dimensional interactions between the fluid flow and the external magnetic field. |
Tuesday, November 21, 2023 9:57AM - 10:10AM |
X30.00010: Energy transfer and third-order law in forced anisotropic MHD turbulence with hyperviscosity Jiang Bin, Cheng Li, Yan Yang, Kangcheng Zhou, William H Matthaeus, Minping Wan The Kolmogorov-Yaglom (third-order) law links energy transfer rates in the inertial range of magneto-hydrodynamic (MHD) turbulence with third-order structure functions. Anisotropy, a typical property in the solar wind, largely challenges the applicability of the third-order law with isotropic assumption. To shed light on the energy transfer process in the presence of anisotropy, the present study conducted direct numerical simulations (DNSs) of forced MHD turbulence with normal and hyper-viscosity under various strengths of the external magnetic field (B_{0}), and calculated three forms of third-order structure function with or without averaging azimuthal or polar angles to B_{0} direction. Correspondingly, three forms of estimated energy transfer rates were studied systematically with various B_{0}. The result shows that the peak of the estimated longitudinal transfer rate occurs at larger scales as closer to the B_{0} direction, and its maximum shifts away from the B_{0 }direction at larger B_{0}. Compared with normal viscous cases, hyper-viscous cases can attain better separation of the inertial range from the dissipation range, thus facilitating the analyses of the inertial range properties and the estimation of the energy cascade rates. We find that the widespread use of the isotropic form of the third-order law in estimating the energy transfer rates is questionable in some cases, especially when the anisotropy arising from the mean magnetic field is inevitable. In contrast, the direction-averaged third-order structure function properly accounts for the effect of anisotropy and predicts the energy transfer rates and inertial range accurately, even at very high B_{0}. With limited statistics, the calculation of the third-order structure function shows a stronger dependence on averaging of azimuthal angles than the time, especially at high B_{0} cases. These findings provide insights into the anisotropic effect on the estimation of energy transfer rates. |
Tuesday, November 21, 2023 10:10AM - 10:23AM |
X30.00011: Multiphase shock-turbulence interactions in decaying magnetohydrodynamic turbulence Justin Kin Jun Hew, Christoph Federrath, Seth Davidovits Studies of shock-turbulence and shock-vortex interactions in sub- and super-Alfvénic magnetised turbulence have major importance in astrophysical plasma flows within the interstellar medium (ISM). Here we conduct high resolution implicit large eddy and direct numerical simulations of magnetohydrodynamic (MHD) turbulence with Lagrangian tracers to investigate the propagation of a cylindrical shock into an inhomogeneous, multiphase medium and study the turbulence and magnetic field amplification in the post-shock mixed region, replicating a similar shock tube experiment being performed at the National Ignition Facility (NIF) of the Lawrence Livermore National Laboratory (LLNL). Simplified theoretical models based on curved shock induced vorticity and Favre-averaged MHD Rankine-Hugoniot relations are used to predict the post-shock Reynolds stress and velocity dispersion, which varies nearly linearly with the average Atwood number in the inhomogenous medium, consistent with the impulsive model for the growth rate of Richtmyer-Meshkov instabilities (RMI) forming in the outer extent of the turbulent, shocked gas. Furthermore, the long-time behaviour of the decay of shock-driven turbulence is also briefly explored. |
Tuesday, November 21, 2023 10:23AM - 10:36AM |
X30.00012: The mechanisms of laminar-turbulent transition in the MHD pipe flow subject to a transverse magnetic field Yelyzaveta Velizhanina, Bernard C Knaepen This study focuses on the mechanisms behind laminar-turbulent transition in the magnetohydrodynamic (MHD) pipe flow in the presence of a transverse magnetic field. In contrast to the hydrodynamic pipe flow, the MHD flow may become linearly unstable owing to the modification of the base flow by the magnetic field. The instability typically occurs when weak velocity jets in the base velocity profile are present and is restricted to certain regimes of the flow when the Reynolds and Hartmann numbers are sufficiently high and the wall of the pipe is electrically conducting. Therefore, subcritical transition induced by perturbations of finite amplitude that arise due to significant transient growth of initially small disturbances may also play a signifcant role. In this context, a three-dimensional perturbation that exhibits the largest transient amplification is then referred to as an optimal perturbation. |
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