Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session B20: Geophysical Fluid Dynamics General II |
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Chair: Michael Le Bars, Aix-Marseille Room: 602 |
Saturday, November 23, 2019 4:40PM - 4:53PM |
B20.00001: A laboratory study of gas giants' zonal jets: formation and long-term evolution Daphne Lemasquerier, Benjamin Favier, Michael Le Bars The stability, structure and dynamics of gas giants' zonal jet streams are still poorly understood, especially in terms of coupling with their deep molecular interior. Here, we use an experimental approach to address the questions of zonal jets formation and long-term evolution. A strong topographic $\beta$-effect is obtained inside a rotating water tank thanks to the paraboloidal shape of the fluid free surface due the centrifugally-induced pressure. The shape of the bottom of the tank is chosen so that this $\beta$-effect is spatially constant. A small-scale turbulent forcing is performed over 128 injection and suction points at the base of the tank allowing a control of its spatio-temporal distribution and intensity. Time-resolving PIV measurements are performed in a horizontal plane. We identify a subcritical bifurcation between two regimes where zonal jets with strong instantaneous signature are present. In the first regime, the jets are weak in amplitude, directly forced and steady. In the second one, we observe self-developed highly energetic jets, independent of the forcing scale. In that last case, the zonal flows kinetic energy spectra are consistent with theoretical predictions in the regime of so-called zonostrophic turbulence relevant to planetary applications. [Preview Abstract] |
Saturday, November 23, 2019 4:53PM - 5:06PM |
B20.00002: ABSTRACT WITHDRAWN |
Saturday, November 23, 2019 5:06PM - 5:19PM |
B20.00003: Shelf flow crossing over a strait: Experimental Joseph Kuehl, Vitalii Sheremet Motivated by the phenomenon of Scotian Shelf Crossover events (Bisagni et al. 1998), a problem of a shelf flow that is interrupted by a strait is considered. Laboratory experiments in a rotating tank with barotropic and baroclinic flow over flat and sloping shelves confirms that the flow is steered by the bathymetric contours and mainly circumnavigates the gulf. In order to jump across the strait, as suggested by earlier theories, the flow must have unrealistically high Rossby numbers. However, the near bottom friction relaxes the bathymetric constraint (Kuehl 2014) and causes the formation of a peculiar jet crossing the strait diagonally. Numerical solutions for realistic values of the frictional parameter reproduce the results of the laboratory experiments and are similar to the patterns observed in the satellite derived sea surface temperature fields (Smith 1983). Bisagni, J. J., R. C. Beardsley, C. M. Rusham, J. P. Manning, and W. Williams, 1996. Deep-Sea Research, 43, 1439-1471. Kuehl, J. J., 2014. Geophysical Research Letters, 41. Smith, P. C., 1983. Journal of Physical Oceanography, 13, 1034-1054. [Preview Abstract] |
Saturday, November 23, 2019 5:19PM - 5:32PM |
B20.00004: Direct Statistical Simulations of a Rotating Thermal Annulus Jeffrey Oishi, Steven Tobias, Brad Marston, Keaton Burns Turbulent systems generate and interact with mean flows in a wide variety of natural systems. Understanding the nature of these interactions, particularly for systems far from equilibrium, remains a paramount priority in understanding large-scale flows on planets and stars. The fundamental problem in studying such systems via direct numerical simulation (DNS) is the fact that the smallest scales can have a significant impact on the mean flows, even when they are very widely separated. One way to make progress is to study the statistics of the flow rather than detailed flow variables themselves. By expanding around the mean flow in terms of equal-time cumulants, we can arrive at a closed set of equations of motion for the cumulants. Here, we present results using an expansion terminated at the second cumulant (CE2) for rapidly rotating thermal convection in an annulus. CE2 discards eddy-eddy interactions that yield eddies; it is fundamentally quasi-linear. We focus on a particular case in which the direct numerical simulation yields an initial three-jet solution that is unstable to a two-jet solution. Interestingly, CE2 predicts a stable three-jet solution, though we find that by biasing the initial conditions to favor certain symmetries, CE2 reproduces the DNS results. [Preview Abstract] |
Saturday, November 23, 2019 5:32PM - 5:45PM |
B20.00005: Mixing in Steady-State Gravity Currents Jim McElwaine, Claudia Cenedese, Jeffrey Heninger Turbidity currents have been observed to propagate for very long distances, longer than one would expect based on the current knowledge of mixing and evolution of gravity currents. Recent DNS simulations suggest that when in steady state the gravity current presents a much more stable interface, potentially reducing the mixing with ambient waters and hence being able to survive and propagate for longer distances. We report experiments that investigate experimentally 'steady state' gravity currents as opposed to lock-release gravity currents, with particular emphasis on the interfacial instability and assess whether the 'flavor'/characteristics of this shear instability and the induced turbulence are different in a steady state scenario as opposed to a more 'transient' scenario which has been investigated using lock-release gravity currents. We report on gravity current experiments in a flume that have reached a statistically steady state and compare the results to those obtained with a classic lock release set up, DNS and theoretical results. [Preview Abstract] |
Saturday, November 23, 2019 5:45PM - 5:58PM |
B20.00006: Effect of Inertial Migration of Particles on Flow Transitions of a Suspension in Taylor--Couette Geometry Lina Baroudi, Alexander Ligay, Madhu Majji, Jeffrey Morris This study presents an experimental investigation into the influence of inertial migration of neutrally buoyant non-Brownian particles on inertial flow transitions of a suspension in Taylor--Couette geometry. A concentric cylinder Taylor-Couette device with a stationary outer cylinder and rotating inner cylinder is considered. The device has an inner to outer radius ratio of 0.1. Starting with the circular Couette flow (CCF) regime with inertially migrated concentration profile in this regime, a lower onset Reynolds number observed when starting with uniform suspension concentration. For inertially migrated concentration profile in CCF, the non-axisymmetric flow states between CCF and Taylor vortex flow (TVF) reported by Majji et al. (JFM 835, 936 (2018)) were also observed here but at lower compared to uniform suspension concentrations. On contrary to the stabilizing effect obtained from the linear stability analysis of CCF with varying viscosity profile in the annular region, our results reveal a destabilizing effect to the CCF due to the inertially migrated concentration profiles. [Preview Abstract] |
Saturday, November 23, 2019 5:58PM - 6:11PM |
B20.00007: Vorticity shedding from a sphere moving vertically in a stratified fluid Hideshi Hanazaki, Tatsuya Yasuda, Koki Takagi, Shinya Okino A numerical study is described of the flow past a sphere moving downward at constant speeds in a stratified fluid. The wake under moderate or strong stratification remains axisymmetric even for $Re > 200$, unlike the flow of a homogeneous fluid which becomes asymmetric for $Re > 200$. A striking feature is that this axisymmetric flow often gives, under moderate stratification, an axisymmetric 'vorticity' shedding, which has never been observed in the wake of an axisymmetric bluff body. In this study, corresponding experiments have also been performed, showing that a non-axisymmetric wake with horizontal fluctuations tend to appear at some heights above the sphere. This suggests that the axisymmetric flow would be hard to be realised in actual flows at high Reynolds numbers ($Re > 200$). [Preview Abstract] |
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