Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session H17: Geophysical Flows: General IV |
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Chair: Keith Julien, University of Colorado Room: 320 |
Monday, November 21, 2011 10:30AM - 10:43AM |
H17.00001: Large-eddy simulation of high Reynolds number gravity and turbidity currents Senthil Radhakrishnan, Mohamad Nasr-Azadani, Eckart Meiburg Gravity and turbidity currents are compositional and particulate laden flows that originate due to the horizontal pressure gradient. High Reynolds number currents are expensive to compute using Direct Numerical Simulation (DNS). Large-eddy simulation (LES) that uses sub-grid parameterization and approximate wall boundary condition provide a cheaper alternative. We have implemented the dynamic Smagorinsky model for sub-grid parameterization and a wall-layer model based on the law of the wall. These parameterizations are employed to simulate gravity and turbidity currents in lock-exchange configuration at high Reynolds number representative of laboratory and field scale currents. We consider current propagation over a flat surface and also past a complex topography. Results from these simulations, in particular, the front evolution and deposit profiles for various values of settling velocity will be discussed. [Preview Abstract] |
Monday, November 21, 2011 10:43AM - 10:56AM |
H17.00002: Zonal jets in thermodynamic shallow water equations with radiative relaxation Paul Dellar, Emma Warneford The thermodynamic shallow water equations treat the reduced gravity as an advected scalar. This allows them to support horizontal variations in temperature, as well as the usual variations in depth and horizontal velocity. Originally proposed for lakes and tropical oceans, we have used them to model the atmospheres of gas giant planets. Adding a radiative cooling term to the temperature evolution equation creates a mass- and momentum-conserving shallow water model that produces super-rotating equatorial jets in our numerical simulations, unlike the sub-rotating jets found in standard shallow water simulations on rotating spheres. We also derive a quasigeostropic version of these equations, in which radiative coupling substantially increases the fraction of kinetic energy accounted for by the zonally-averaged flow in forced-dissipative simulations. Finally, we derive further reduced models in the limit of rapid radiative relaxation. [Preview Abstract] |
Monday, November 21, 2011 10:56AM - 11:09AM |
H17.00003: Physical balances in non-hydrostatic balanced quasi-geostrophic equations Keith Julien, Antonio Rubio, Ian Grooms A suite of high resolution DNS for Rotating Rayleigh Benard convection using the non-hydrostatic balanced geostophic equations (NHBGE) (Julien et al 1998, 2006) over a wide range of parameter space was conducted to allow for the analysis of the term-by-term balances of the prognostic equations. These reduced equations offer greater access to the Low Rossby limit of thermal convection in comparison to the DNS of incompressible Navier-Stokes. The result has been a greater understanding of the transition between three regimes (cellular, columns, geostrophic turbulence) in terms of physical balances. Particularly, analysis reveals a dynamically unstable thermal boundary layer that can be modeled and turbulent interiors for which scalings with thermal forcing can be understood. Further insight has been gained into the scaling and breakdown of the convective Taylor columns (CTCs) (Grooms et al PRL, 2011) and the equation balances inside and outside of the CTCs in regimes where they coexist with cellular solutions. [Preview Abstract] |
Monday, November 21, 2011 11:09AM - 11:22AM |
H17.00004: The Investigation of Wind Waves in Persian Gulf by Multi-level Long-term Hindcasts and In-situ Measurements Ying-Po Liao, Arindam Singha, James M. Kaihatu, Reza Sadr In this study, we employ both numerical and experimental methodologies to investigate the spatially and seasonally varying wind-wave features in the Persian Gulf and near Qatar due to the seasonal shamal. We perform a multi-level nested long-term wave hindcast using the SWAN wave model and five years of wind data from COAMPS (2004-2008), with emphasis on the area near Doha Port. A weather station, a stack of anemometers, and two video cameras are installed at Doha Port and will measure wind velocity profiles and wave kinematics/dynamics. These will be used to validate the climatology, as well as providing new insights into the physics of wind wave generation. [Preview Abstract] |
Monday, November 21, 2011 11:22AM - 11:35AM |
H17.00005: Walking with coffee: when and why coffee spills Hans C. Mayer, Rouslan Krechetnikov In our busy lives, almost all of us have to walk with a cup of coffee. Needless to say, under certain conditions we spill that precious liquid. This is a common example of the interplay between the mechanics of the complex motion of a walking individual and the fluid dynamics of a low viscosity liquid contained in a cup. We report on the results of an experimental investigation undertaken to explore the particular conditions under which coffee spills. Frame-by-frame analysis of recorded movies helps to elucidate the trajectory of the cup for various walking speeds and initial liquid levels. These kinematics, including both regular and irregular motions, are connected to instances during walking that result in spilled liquid. The coupling between mechanical aspects of walking and the fluid motion are analyzed based on which we determine a basic operational space with which one can confidently walk with cup in hand. [Preview Abstract] |
Monday, November 21, 2011 11:35AM - 11:48AM |
H17.00006: Propagation of meteor infrasound in layered atmospheres Christophe Millet, Christophe P. Haynes In the present work, we provide a theoretical model of the shock wave generated by the atmospheric entry of meteors. Such a shock wave propagates from a strong blast wave region out to the far-field acoustic limit. The matching of the two regions is possible through a shape factor K, which is considered to be a random variable. The amplitude and period of the N-wave signal are obtained using Whitham's nonlinearization method for cylindrical waves. The method has been used to re-examine the crater-forming meteorite fall near Carancas, Peru (2007). As the specific trajectory of the meteor is unknown, all outcomes of the signal have been statistically analyzed. This includes finding the probability of a given signal and how the factor K affects this probability. Even though there is a good agreement between the period of the N-wave signal and the recorded signal, it is shown that a homogeneous isothermal atmospheric assumption leads to large errors in the ballistic overpressure relative to the observed values. Despite this, we demonstrate that inclusion of atmospheric absorption and meteoritic ablation within the model leads to the correct ground acoustic impulse. Future work involves a similar study for randomly layered atmospheres and will focus on the role of small-scale inhomogeneities. [Preview Abstract] |
Monday, November 21, 2011 11:48AM - 12:01PM |
H17.00007: Lubrication Effect of Sea Spray under High-wind Conditions Yevgenii Rastigejev, Sergey Suslov, Yuh-Lang Lin Accurate modeling of sea spray under high-wind conditions is essential for improving intensity forecast of hurricanes or severe storms. It has been shown that the presence of water droplets in the vortex of hurricane leads to a significant reduction in turbulent intensity and consequently to a sharp flow acceleration. In this study, several mathematical models are proposed to detail the influence of sea spray on vertical momentum transport. The models are based on: turbulent kinetic energy (TKE) equation, E-$\varepsilon $ closure and the Monin-Obukhov similarity (MOS) theory. It is demonstrated that for values larger than the critical speed, the spray concentration rapidly increases, which results in significant flow acceleration. All models produce qualitatively similar results for all turbulent flow parameters considered. It was found that the MOS-based and E-$\varepsilon $ models tend to predict noticeably stronger lubrication effect than TKE model, especially for slower wind speeds. The results of calculations are in very good agreement with available experimental data. The work is supported by NOAA, NA06OAR4810187 and NSF, HRD-1036563 grants. [Preview Abstract] |
Monday, November 21, 2011 12:01PM - 12:14PM |
H17.00008: Evolution of a Mushy Zone on a Finite Domain Nicholas Gewecke, Tim Schulze Mushy zones are regions of intermixed liquid and solid which result from instability due to the build-up of solute during solidification of multispecies materials. Transient dynamics in the case of a very cold lower boundary for a finite-depth tank lead to variations in the amount of solute which is frozen into the solid, which contrasts with the dynamics on an infinite domain. Furthermore, the growth of the solid layer eventually leads to the elimination of the mushy layer over very long time scales, which may be of interest in geological settings such as solidification of sea ice or magma chambers. [Preview Abstract] |
Monday, November 21, 2011 12:14PM - 12:27PM |
H17.00009: Lava flow dynamics driven by temperature-dependent viscosity variations Serina Diniega, Suzanne Smrekar, Steven Anderson, Ellen Stofan As lava viscosity can change 1-2 orders of magnitude due to small changes in temperature, several studies have predicted the formation of low-viscosity/high-speed ``fingers'' (similar to a Saffman-Taylor type instability). Through the use of numerical simulation and steady-state analysis of model equations, we identify solutions that provide pahoehoe lava flows with a natural mechanism for the formation of channels within a sheet flow. We assume Hele-shaw-type geometry, Newtonian/laminar fluid flow, a Nahme's exponential law relating temperature and viscosity, and radiative heat-loss. Preliminary results indicate that flow-focusing occurs rapidly, but that the system settles into a new steady-state and does not create perpetually-lengthening hot-fingers. This suggests that additional physical processes are needed for the continued growth of preferred flow zones. This work has application to both Earth and planetary volcanology studies as the emplacement mechanics that yield long lava flows are not yet well understood. [Preview Abstract] |
Monday, November 21, 2011 12:27PM - 12:40PM |
H17.00010: Mixing and entrainment in mantle plumes: A 3D experimental investigation William Newsome, Aline Cotel, Carolina Lithgow-Bertelloni, Stanley Hart, John Whitehead Significant differences exist between isotopic signatures of typical mid-ocean ridge basalts (MORB) and those associated with many ocean islands, with ocean island basalts (OIB) generally exhibiting more variability in trace element concentrations and also a bias towards enrichment in radiogenic isotopes such as Sr, Nd, Hf and Pb. Such observations coupled with other geophysical evidence have been used to suggest that OIB's are surface manifestations of thermal plumes originating in the deep interior near the core-mantle boundary that interact with distinct, heterogeneous reservoirs as material is transported from the Earth's interior to the surface. We experimentally investigate the structure and transport characteristics of isolated thermal plumes in corn syrup. The 3D velocity field is measured using a scanning stereoscopic particle image velocimetry system. Two types of tracer particles are simultaneously utilized, with thermochromic liquid crystals providing an estimate of the temperature field. Lagrangian coherent structures computed from the velocity field identify key material lines and surfaces that provide a taxonomic picture of plumes operating in different regimes. These govern how the plume interacts with the ambient during its ascent. [Preview Abstract] |
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