Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session M34: Geophysical Fluid Dynamics: Special Topics IIGeophysical
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Chair: Ian Grooms, University of Colorado Room: 102 |
Tuesday, November 21, 2017 8:00AM - 8:13AM |
M34.00001: Swirling plumes and spinning tops Daria Frank, Julien Landel, Stuart Dalziel, Paul Linden Motivated by potential effects of the Earth's rotation on the dynamics of the oil plume resulting from the Deepwater Horizon disaster in 2010, we conducted laboratory experiments on saltwater and bubble axisymmetric point plumes in a homogeneous rotating environment. The effect of rotation is conventionally characterized by a Rossby number, based on the source buoyancy flux, the rotation rate of the system and the total water depth and which ranged from 0.02 to 1.3 in our experiments. In the range of parameters studied, we report a striking new physical instability in the plume dynamics near the source. After approximately one rotation period, the plume axis tilts away laterally from the centreline and the plume starts to precess in the anticyclonic direction. We find that the mean precession frequency of the plume scales linearly with the rotation rate of the environment. Surprisingly, the precession frequency is found to be independent of the diameter of the plume nozzle, the source buoyancy flux, the water depth and the geometry of the domain. In this talk, we present our experimental results and develop simple theoretical toy models to explain the observed plume behaviour. [Preview Abstract] |
Tuesday, November 21, 2017 8:13AM - 8:26AM |
M34.00002: ABSTRACT WITHDRAWN |
Tuesday, November 21, 2017 8:26AM - 8:39AM |
M34.00003: Experimental approach a flows driven by latitudinal librations in a triaxial ellipsoid jerome Noir, Yoann Charles Planetary cores and subsurface oceans dynamics are fundamental to derive accurate models of orbital evolution of planets and magnetic field generation. Primarily in solid body rotation, the interior fluid is subject to various sources of perturbations, thermo-chemical convection, precession and nutations, Librations of the surrounding shell or solid tides. In the present study we developed an experimental approach of the latitudinal libration in a triaxial ellipsoid. We first present the laminar regime, the direct excitation of a Poincare mode, we show that the theoretically predicted resonance frequency is well recovered and that the finite amplitude of libration leads to a non-linear shift of the asymptotic value. In a second part, we investigate the unstable regimes; we show that the underlying destabilization mechanism is in the form of a parametric resonance between pairs of inertial modes. The system exhibits two branches of parametric resonances with a bi-stability dynamics in a narrow range of parameters. [Preview Abstract] |
Tuesday, November 21, 2017 8:39AM - 8:52AM |
M34.00004: Semi-Numerical Studies of the Three-Meter Spherical Couette Experiment Utilizing Data Assimilation Sarah Burnett, Ruben Rojas, Artur Perevalov, Daniel Lathrop, Kayo Ide, Nathanael Schaeffer The model of the Earth's magnetic field has been investigated in recent years through experiments and numerical models. At the University of Maryland, experimental studies are implemented in a three-meter spherical Couette device filled with liquid sodium. The inner and outer spheres of this apparatus mimic the planet's inner core and core-mantle boundary, respectively. These experiments incorporate high velocity flows with Reynolds numbers $\sim 10^8$. In spherical Couette geometry, the numerical scheme applied to this work features finite difference methods in the radial direction and pseudospectral spherical harmonic transforms elsewhere [Schaeffer, N. G3 (2013)]. Adding to the numerical model, data assimilation integrates the experimental outer-layer magnetic field measurements. This semi-numerical model can then be compared to the experimental results as well as forecasting magnetic field changes. Data assimilation makes it possible to get estimates of internal motions of the three-meter experiment that would otherwise be intrusive or impossible to obtain in experiments or too computationally expensive with a purely numerical code. If we can provide accurate models of the three-meter device, it is possible to attempt to model the geomagnetic field. [Preview Abstract] |
Tuesday, November 21, 2017 8:52AM - 9:05AM |
M34.00005: Study of rotating convection in a new configuration with simultaneous imposition of radial and vertical temperature gradients Ayan Kumar Banerjee, Amitabh Bhattacharya, Sridhar Balasubramanian Laboratory experiments were conducted in a novel configuration, comprising of non-homogeneously heated rotating cylindrical annulus, to study dynamics of rotating convection. This configuration allows co-existence of convective plumes and baroclinic instabilities, which characterizes geophysical flows. Localized temperature time series data acquired by thermocouples, combined with 2D axisymmetric ANSYS Fluent simulation were used to understand the physics of baroclinic instabilities, convective structures and their interaction. Scaling for the proposed system is derived and validated with thermal measurements. [Preview Abstract] |
Tuesday, November 21, 2017 9:05AM - 9:18AM |
M34.00006: On effects of topography in rotating flows Fabian Burmann, Jerome Noir, Andrew Jackson Both, seismological studies and geodynamic arguments suggest that there is significant topography at the core mantle boundary (CMB). This leads to the question whether the topography of the CMB could influence the flow in the Earth's outer core. As a preliminary experiment, we investigate the effects of bottom topography in the so-called Spin-Up, where motion of a contained fluid is created by a sudden increase of rotation rate. Experiments are performed in a cylindrical container mounted on a rotating table and quantitative results are obtained with particle image velocimetry. Several horizontal length scales of topography ($\lambda$) are investigated, ranging from cases where $\lambda$ is much smaller then the lateral extend of the experiment ($R$) to cases where $\lambda$ is a fraction of $R$. We find that there is an optimal $\lambda$ that creates maximum dissipation of kinetic energy. Depending on the length scale of the topography, kinetic energy is either dissipated in the boundary layer or in the bulk of the fluid. Two different phases of fluid motion are present: a starting flow in the from of solid rotation (phase I), which is later replaced by meso scale vortices on the length scale of bottom topography (phase II). [Preview Abstract] |
Tuesday, November 21, 2017 9:18AM - 9:31AM |
M34.00007: Transport by deep convection in buoyancy-forced circulation in a rotating basin Catherine Vreugdenhil, Bishakhdatta Gayen, Ross Griffiths We use direct numerical simulations of buoyancy-forced circulation in a rotating $f$-plane basin to examine transport by geostrophic flow and deep convection. The domain is a closed rectangular box with vertical and horizontal aspect ratios of $A=0.16$ and $A_y=0.24$ respectively. Half the base is cooled and half is heated to achieve Rayleigh numbers $Ra\approx 10^{12}-10^{13}$, where $Ra$ defined in terms of domain length $L$. Ekman number is varied as $E\approx 10^{-7}-10^{-5}$ and Prandtl number is $Pr=5$. The results show that circulation and heat throughput are governed by horizontal geostrophic flow in the thermal boundary layer and are functions of a convective Rossby number. Vertical heat transport is mostly by open-ocean chimney convection; mean vertical transport of water is both in chimneys and against side boundaries. We calculate energy budgets and, for the $Ra$ available here, the energy sinks of dissipation and irreversible mixing are largely confined to the thermal boundary layer. For small Rossby numbers relevant to the ocean the results imply that heat throughput and mean circulation are controlled by geostrophic flow and boundary currents, while vertical heat transport from the surface layer into the deep interior occurs mostly in open-ocean chimney convection. [Preview Abstract] |
Tuesday, November 21, 2017 9:31AM - 9:44AM |
M34.00008: The energetics of rotating wind-forced horizontal convection Varvara Zemskova, Brian White, Alberto Scotti We present numerical results for rotating, wind-forced horizontal convection as a simple model for the Southern Ocean branch of the Meridional Overturning Circulation. The flow is driven by differential buoyancy forcing applied at the top surface, with cooling at one end (to represent the pole) and warming at the other (the equatorial region) and a zonally re-entrant channel to represent the Antarctic Circumpolar Current. Zonal wind forcing is applied with a similar pattern to the westerlies and with varying magnitude relative to the buoyancy forcing. The problem is solved numerically using a 3D DNS model based on a finite-volume solver for the Boussinesq Navier-Stokes equations with rotation. The overall dynamics, such as large-scale overturning, baroclinic eddying, turbulent mixing, and energy cascades are investigated using the local Available Potential Energy framework introduced in [Scotti and White, \textit{JFM}, 2014]. We find that the magnitude and shape of the zonal wind stress profile are important to the spatial pattern of the overturning circulation. However, the essential circulation and the energetics in cases with wind are similar to the base case with buoyancy forcing alone, suggesting that surface APE generation by buoyancy forcing is dominant in setting the circulation. [Preview Abstract] |
Tuesday, November 21, 2017 9:44AM - 9:57AM |
M34.00009: A Precipitating Moist Rayleigh-Bénard Convection Model Hao Fu, Yihua Lin In order to derive a simple atmospheric moist convection model, the classical Rayleigh-Bénard convection model has been extended to include water phase change by Bretherton (1986) and Pauluis (2010). The stratification is “conditionally unstable”, with statically unstable saturated region and stable unsaturated region. We derived a simple precipitation scheme from basic thermodynamic principle, with three additional non-dimensional parameters characterizing rain formation time scale, rain fall speed and rain evaporation time scale. A Boussinesq CFD code in vorticity-velocity formation was developed to solve the equation set. In a thermal bubble simulation which resembles isolated convective storm, the precipitation cold pool and density current has been successfully reproduced. The model is further used to simulate free moist convection whose non-precipitating counterpart has been done by Pauluis (2011). Self-aggregated convection has been reproduced and the effect of evaporation-induced density current on convection lifecycle will be discussed. [Preview Abstract] |
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