Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session MS: Geophysical: General I |
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Chair: Eckart Meiburg, University of California, Santa Barbara Room: 200G |
Tuesday, November 24, 2009 8:00AM - 8:13AM |
MS.00001: Laboratory scale simulation of spontaneous vertical convective vortex generation Albert Sharifulin, Anatoly Poludnitsin The new mechanism of spontaneous vertical vortex generation in stratified fluid is under consideration. This phenomenon was discovered in the framework of experimental attempt [1] to proof the hypothesis of universal character of bifurcation curve formulated in [2]. The experiment with slow cubic cell inclination from bottom heating position was performed. The theoretically predicted curve form had been proved; but in the transition process from abnormal convection flow to normal one during bifurcation curve crossing the unexpected spontaneous vertical convective vortex motion has been discovered. Possibility of spontaneous vertical convective vortex generation application to atmospheric behavior explanation and to Earth's mantle one is discussed. New non-local hurricane generation mechanism and observed oceanic volcano archipelago's form explanation attempt are formulated and speculated. [1] AN Sharifulin, AN Poludnitsin, AS Kravchuk Laboratory Scale Simulation of Nonlocal Generation of a Tropical Cyclone. Journal of Experimental and Theoretical Physics, 2008, V.107, No.6, p.1090. [2] AI Nikitin, AN Sharifulin, Concerning the bifurcations of steady-state thermal convection regimes in a closed cavity due to the Whitney folding-type singularity. Heat Transfer -- Soviet Research, v.21, no.2, 1989, p.213. [Preview Abstract] |
Tuesday, November 24, 2009 8:13AM - 8:26AM |
MS.00002: Frontal instabilities and waves in a differentially rotating two-layer fluid Jan-Bert Flor, Helene Scolan Fronts are key structures for ocean and atmosphere dynamics and relevant for weather forecasts and climate. In this study, we have investigated the stability of a baroclinic front, generated in a rotating salt-stratified two-layer fluid by a rotating lid at the surface of the fluid. In the parameter space set by rotational Froude number, dissipation (i.e. spin-down to disk rotation time-ratio) and Rossby number, different flow regimes are observed, ranging from axisymmetric, Kelvin Helmholtz instability to irregular baroclinic instable flows, in coherence with former results obtained for two- layer flows in immiscible fluids. New is the evidence of the Rossby-Kelvin instability, which occurs as a consequence of the resonant interaction between Rossby and Kelvin waves. In addition, locally emitted waves with a short wave length are observed in the baroclinic unstable regime. Some of these waves appear for relatively high Richardson numbers, but for wave numbers for which one may also expect Holmboe waves. We discuss these waves in the light of spontaneously emitted inertia-gravity waves and other possible mechanisms. [Preview Abstract] |
Tuesday, November 24, 2009 8:26AM - 8:39AM |
MS.00003: Trapping and hopping of a large ``continent" over a thermally convecting fluid Jun Zhang, Jin-Qiang Zhong, Bin Liu In an annular geometry, we study the interactions between a freely moving, floating boundary and a thermally convective fluid underneath. This experiment aims to investigate the essentials of interplay between large continents and a convective mantle. We find that the continent, depending on its relative size, can be trapped over a convergent or divergent flow at the continent-mantle interface. Such trapped states are regularly interrupted as the continent hops from one trapping position to the other. This rich dynamics can be understood by the heat buildup beneath the continent, a phenomenon referred to as the ``thermal blanket" effect in geophysics. [Preview Abstract] |
Tuesday, November 24, 2009 8:39AM - 8:52AM |
MS.00004: Melt Conduit Instability John Whitehead, Miranda Holmes-Cerfon Very long conduits of melt, (lava tubes, magma conduits, glacial drainage tubes) exist in many locations. An idealized model and its stability is analyzed to answer ``how far can the fluid flow and remain liquid''? Laboratory experiments show that when a liquid flows in a pipe with the boundary temperature below freezing, a tubular drainage conduit is surrounded by solidified material. When the flow rate into the pipe is set below a fixed value, the tube freezes shut. As flow rate is gradually changed downward toward the freezing value, pressure change across the pipe rises to a maximum, a result that is not in accord with previous theory. A theoretical model allows for a change in radius in the flow direction (similar to some previous injection molding studies), with a mixed pressure-flux upstream boundary condition. Linear stability analyses of this and a simplified model indicate that: (i) for fixed flux, the tube can be infinitely long with minimum pressure as flux is varied; (ii) for fixed pressure drop across the tube, this minimum determines a maximum length; (iii) for the mixed pressure-flux condition, a stable tube exceeds this length. This is a possible explanation for the previously unexplained experimental pressure maximum near freezing. Therefore, distance traveled by melt within the earth might be very sensitive to the conditions that govern upstream pressure and flow rate. [Preview Abstract] |
Tuesday, November 24, 2009 8:52AM - 9:05AM |
MS.00005: Modelling of Transport and Mixing across Gulf Stream Tatyana Krasnopolskaya, Vladimir Il'chenko, Vyacheslav Meleshko, Olena Stetsenko The new mathematical model for a stream function of a meandering jet of Gulf Stream is suggested based upon a modification of the von K\'arm\'an vortex street stream function. This stream function allows to approximate experimentally found by Bower main coherent structure elements of Gulf Stream in a coordinate frame moving with a speed of the meander: i) an eastward-propagating meandering jet; ii) regions of fluid recirculation below and above meander crests and troughs; iii) regions of westward-propagating fluid below and above the jet and recirculation regions. The inclusion of eddies above the recirculation regions and the jet enhance transport and mixing across the jet. Calculations show that more than one third of the circular area above hyperbolic points may contain warm fluid from a central area of the jet. To study mixing across the jet we examine deformation of this circular area back in time, so we can determine from which part of the jet that area is composed. Contour line tracking method conserving all topological properties in 2-D flows is used for this procedure. [Preview Abstract] |
Tuesday, November 24, 2009 9:05AM - 9:18AM |
MS.00006: Gravity currents in a stratified ambient fluid Michael Patterson, Andrew Aspden Motivated by the previous study of Maxworthy et al. 2002 we revisit the problem in which a lock release gravity current propagates into a stratified ambient fluid. High-resolution three-dimensional numerical simulations based on ILES framework are used in conjunction with a simple box model to develop a greater understanding of the complex interactions between the slumping gravity current and the internal waves that develop. Examination of the energetics of the system are carried out for both sub and super-critical gravity currents. The results show that for the sub-critical gravity currents the energy passed from the gravity current to the wave field and subsequently from the wave field back to the gravity current. Calculations of the energy transfer between the gravity current and the internal wave field will be presented. [Preview Abstract] |
Tuesday, November 24, 2009 9:18AM - 9:31AM |
MS.00007: Fracturing of rocks by ice Ioanna Vlahou, M. Grae Worster Frost damage, caused by the freezing of water-saturated media, affects plant roots, pavements and the foundations of buildings, and is a major erosional force in rocks. The process has been studied extensively in the case of soils, and mechanisms such as the formation of ice lenses have been identified. Here, we consider the freezing of water in a three-dimensional cavity in a water-saturated, porous, elastic rock. Initially, the expansion of water as it freezes causes flow away from the solidification front, into the porous rock. The Darcy flow in the porous medium controls the pressure field and therefore the freezing temperature. At later times, disjoining thermomolecular forces create a pre-melted film of water between the ice and the rock and cause flow of pore water from the surrounding rock into the cavity. We find that the disjoining forces between the ice and the rock have the dominant effect, so we focus on those later times when the cavity is ice-filled. We solve the coupled set of integro-differential equations governing the elastic stress in the rock and the flow through its pores to determine the evolution of the shape and extent of the ice-filled cavity. [Preview Abstract] |
Tuesday, November 24, 2009 9:31AM - 9:44AM |
MS.00008: Non-Boussinesq axisymmetric gravity currents at high Re Marius Ungarish The propagation of a non-Boussinesq gravity current in an axisymmetric configuration (full cylinder or wedge) is considered. The current of density $\rho_c$ is released from rest from a lock of radius $r_0$ and height $h_0$ into an ambient fluid of density $\rho_a$ in a container of height $H$, adjacent to the horizontal boundary on which propagation occurs. When the Reynolds number Re is large, the resulting flow is governed by the parameters $\rho_c/\rho_a$ and $H^{\ast} = H/h_0$. We show that the shallow-water one layer model, carefully combined with a Benjamin-type front condition, provides a versatile formulation for the thickness and speed of the current, for a wide range of the parameters, without any adjustable constants. (The Boussinesq currents are just a small subdomain about $\rho_c/\rho_a = 1$ of this solution). Comparisons with Navier-Stokes solutions and differences with the 2D rectangular counterpart (Ungarish, J. Fluid Mech. 579, 373-382, 2007) are discussed. [Preview Abstract] |
Tuesday, November 24, 2009 9:44AM - 9:57AM |
MS.00009: A numerical study of the energy flux in internal bores Zachary Borden, Eckart Meiburg Internal bores, or hydraulic jumps, arise in many atmospheric and oceanographic phenomena. The classic single-layer hydraulic jump model accurately predicts a bore's behavior when the density difference between the expanding and contracting layer is large (i.e. water and air), but fails in the Boussinesq limit. A two-layer model, where mass is conserved separately in each layer and momentum is conserved globally, does a much better job but requires for closure an assumption about the loss of energy across a bore. It is widely agreed that assuming all the energy loss occurs entirely in one of the layers puts bounds on a bore's propagation speed. However, under some circumstances, both assumptions over-predict the propagation speed, implying an energy gain in the expanding layer. We directly examine the flux of energy within internal bores using 2D direct numerical simulations. We find that although there is a global loss of energy across the bore, there is a transfer of energy from the contracting to the expanding layer causing a net energy gain in that layer. The transfer is largely the result of the horizontal pressure gradient caused by a difference in hydrostatic pressure across the bore. [Preview Abstract] |
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