Bulletin of the American Physical Society
74th Annual Meeting of the APS Division of Fluid Dynamics
Volume 66, Number 17
Sunday–Tuesday, November 21–23, 2021; Phoenix Convention Center, Phoenix, Arizona
Session F29: Geophysical Fluid Dynamics: Rotating |
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Chair: Pedram Hassanzadeh, Rice Room: North 229 A |
Sunday, November 21, 2021 5:25PM - 5:38PM Not Participating |
F29.00001: Connections between slowly and rapidly rotating convection scalings: Rise of the Rossby numbers Jonathan M Aurnou, Susanne Horn, Keith A Julien We will present transport scalings for slowly and rapidly rotating turbulent convection systems, with the end goals of both explaining differences and forging connections between the regimes. Through the selection of physically relevant estimates for length $\ell$, velocity $U$ and temperature scales $\vartheta$ in each regime, turbulent scalings are developed for the local Reynolds $Re_\ell = U \ell /\nu$; local P\'eclet $Pe_\ell = U \ell /\kappa$; and Nusselt number $Nu = U \vartheta/(\kappa \Delta T/H)$. Emergent from the scaling analyses is a unified continuum based on a single external control parameter, the convective Rossby number, $\RoC = \sqrt{g \alpha \Delta T / (4 \Omega^2 H)}$, which is found to scale with the local Rossby number $\Rol \sim \RoC$ in both the slowly and rapidly rotating regimes, explaining the ubiquity of $\RoC$ in studies of rotating convection dynamics, convection-driven zonal jet generation and planetary dynamo generation. |
Sunday, November 21, 2021 5:38PM - 5:51PM |
F29.00002: Magnetic Field Amplification at the Maximum Torque State in a 1000 Rm Spherical Couette Experiment. Ruben E Rojas, Artur Perevalov, Douglas R Stone, Daniel S Zimmerman, Santiago A Triana, Daniel P Lathrop The search for a spherical Couette magnetic dynamo in the laboratory continues. The dynamo action is the process through which a magnetic field is amplified and sustained by electrically conductive flows. This is an ubiquitous phenomenon in nature: Galaxies, stars and planets, all exhibit magnetic field amplification by their conductive constituents. At the University of Maryland our 3-m diameter spherical Couette experiment uses liquid sodium between concentric spheres to mimic some of the dynamics of these flows. We are now progressing from the previous amplified magnetic fields toward a possible dynamo state based on adding baffles to the inner sphere. While the modifications take place we focus our attention on previous unpublished experimental runs with a smooth inner sphere that achieved substantial amplification of the magnetic field but without dynamo generation. We present magnetic field amplification as a function of the different experimental parameters including Reynolds and Rossby numbers. Thanks to recent studies in a hydrodynamic scale model, we can bring a better insight into these results and propose locations in the parameter space of the experiment as possible candidates for a dynamo generation given the forthcoming modifications that are currently taking place. |
Sunday, November 21, 2021 5:51PM - 6:04PM |
F29.00003: Machine learning predictions of high Reynolds number rotating MHD turbulence Artur Perevalov, Ruben E Rojas, Brian R Hunt, Daniel P Lathrop Machine learning has been used to predict the time evolution of complex systems. Here we investigate the predictability of a spherical Couette high Reynolds number MHD experiment, using a recurrent neural network technique called reservoir computing, an auto-regressive model, and a hybrid combination of these two methods. These methods do not use a physical model. We analyze how their performance changes with different amounts of training data, and different fluid dynamical states. |
Sunday, November 21, 2021 6:04PM - 6:17PM |
F29.00004: Predicting Magnetic Fields for the Three-Meter Spherical Couette Experiment Sarah C Burnett, Nathanaël Schaeffer, Kayo Ide, Daniel P Lathrop The magnetohydrodynamics of Earth has been explored through experiments, numerical models, and machine learning. The interaction between Earth's magnetic fields and its outer core is replicated in a laboratory using the three-meter spherical Couette device filled with liquid sodium driven by two independently rotating concentric shells and an external dipole magnetic field. Recently, this experiment has been modified to come closer to replicating the convection-driven flows of Earth. The experiment takes sparse measurements of the external magnetic field. XSHELLS solves the coupled Navier-Stokes and induction equations numerically to give the full velocity and magnetic field up to a turbulent limit due to resolution. In these studies, we compare the experimental magnetic field measurement with the extrapolated surface magnetic field measurements in simulations using principal component analysis by matching all parameters but the level of turbulence. Our goal is to see if (i) the eigenvectors corresponding to the largest eigenvalues are comparable and (ii) how then the surface measurements of the simulation couple with the internal measurements, which are not accessible in the experiment. These studies provide insight on the measurements required to predict Earth's magnetic field. |
Sunday, November 21, 2021 6:17PM - 6:30PM |
F29.00005: Effects of Thermal Boundary Condition on the Formation of Tropical Cyclone-like Vortex in Rotating Convection Veeraraghavan Kannan, Nedunchezhian Swaminathan, Peter Davidson Past studies empirically showed that there is a specific combination of Reynolds and Ekman numbers in rotating convective flows of a Boussinesq fluid allowing the formation of a tropical cyclone-like vortex (TCLV) with an eye. Axisymmetric flows with adiabatic sidewall were considered in those studies. We seek to find an answer to the question, would TCLV appear if the axisymmetric conditions are relaxed for the same Reynolds and Ekman numbers? This objective is addressed by conducting rotating convective flow simulations in a shallow cylindrical domain with the same boundary conditions (BCs) used for the axisymmetric calculations. It is observed that the flow becomes chaotic with no TCLV, however, TCLV emerges when the sidewall BC is changed from adiabatic to isothermal. This is because of a localised retrograde travelling wave near the sidewall which helps the emergence of a stronger primary poloidal flow leading to the formation of TCLV. This is observed for a range of Reynolds and Ekman numbers. |
Sunday, November 21, 2021 6:30PM - 6:43PM |
F29.00006: Three-dimensionality of the triadic resonance instability of a plane inertial wave Daniel A Mora-Paiba, Eduardo Monsalve, Maxime Brunet, Thierry Dauxois, Pierre-Philippe Cortet We analyze theoretically and experimentally the triadic resonance instability (TRI) of a plane inertial wave in a rotating fluid. Building on the classical triadic interaction equations between helical modes, we show by numerical integration that the maximum growth rate of the TRI is found for secondary waves that do not propagate in the same vertical plane as the primary wave (the rotation axis is parallel to the vertical). In the inviscid limit, we prove this result analytically, in which case the change in the horizontal propagation direction induced by the TRI evolves from 60 to 90 degrees depending on the frequency of the primary wave. Thanks to a wave generator with a large spatial extension in the horizontal direction of invariance of the forced wave, we are able to report experimental evidence that the TRI of a plane inertial wave is three-dimensional. The wave vectors of the secondary waves produced by the TRI are shown to match the theoretical predictions based on the maximum growth rate criterion. These results reveal that the triadic resonant interactions between inertial waves are very efficient at redistributing energy in the horizontal plane, normal to the rotation axis. |
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