Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session A10: Convection and Buoyancy Driven Flows: Environmental |
Hide Abstracts |
Sponsoring Units: DFD GPC Chair: Kiran Bhaganagar, University of Texas, San Antonio Room: B118-119 |
Sunday, November 20, 2016 8:00AM - 8:13AM |
A10.00001: Simulation of plume rise: Study the effect of stably stratified turbulence layer on the rise of a buoyant plume from a continuous source by observing the plume centroid Sudheer Reddy Bhimireddy, Kiran Bhaganagar Buoyant plumes are common in atmosphere when there exists a difference in temperature or density between the source and its ambience. In a stratified environment, plume rise happens until the buoyancy variation exists between the plume and ambience. In a calm no wind ambience, this plume rise is purely vertical and the entrainment happens because of the relative motion of the plume with ambience and also ambient turbulence. In this study, a plume centroid is defined as the plume mass center and is calculated from the kinematic equation which relates the rate of change of centroids position to the plume rise velocity. Parameters needed to describe the plume are considered as the plume radius, plumes vertical velocity and local buoyancy of the plume. The plume rise velocity is calculated by the mass, momentum and heat conservation equations in their differential form. Our study focuses on the entrainment velocity, as it depicts the extent of plume growth. This entrainment velocity is made up as sum of fractions of plume's relative velocity and ambient turbulence. From the results, we studied the effect of turbulence on the plume growth by observing the variation in the plume radius at different heights and the centroid height reached before loosing its buoyancy. [Preview Abstract] |
Sunday, November 20, 2016 8:13AM - 8:26AM |
A10.00002: Monitoring of Carbon Dioxide and Methane Plumes from Combined Ground-Airborne Sensors Jamey Jacob, Taylor Mitchell, Wes Honeycutt, Nicholas Materer, Tyler Ley, Peter Clark A hybrid ground-airborne sensing network for real-time plume monitoring of CO$_2$ and CH$_4$ for carbon sequestration is investigated. Conventional soil gas monitoring has difficulty in distinguishing gas flux signals from leakage with those associated with meteorologically driven changes. A low-cost, lightweight sensor system has been developed and implemented onboard a small unmanned aircraft and is combined with a large-scale ground network that measures gas concentration. These are combined with other atmospheric diagnostics, including thermodynamic data and velocity from ultrasonic anemometers and multi-hole probes. To characterize the system behavior and verify its effectiveness, field tests have been conducted with simulated discharges of CO$_2$ and CH$_4$ from compressed gas tanks to mimic leaks and generate gaseous plumes, as well as field tests over the Farnsworth CO$_2$-EOR site in the Anadarko Basin. Since the sensor response time is a function of vehicle airspeed, dynamic calibration models are required to determine accurate location of gas concentration in space and time. Comparisons are made between the two tests and results compared with historical models combining both flight and atmospheric dynamics. [Preview Abstract] |
Sunday, November 20, 2016 8:26AM - 8:39AM |
A10.00003: Dynamics of Downdrafts Emily Kruger, Henry Burridge, Jamie Partridge, Gabriel Rooney, Paul Linden Downward moving cold air witin thunderstorms, known as downdrafts, can be used to determine the severity of a storm. Therefore an understanding of them is useful for weather forecasting. Typically in weather forecasting these downdrafts are modelled using the theory of a plume from from Morton, Taylor and Turner (1956), which inherintly assumes that the plume is long and thin. Downdrafts are generally wider than they are high and hence deviate from the Morton, Taylor and Turner theory. We perform experiments using finite releases of dense fluid from large area sources, releasing a range of volumes of fluids from a cylinder, at a range of heights above the ground which encompasses the typical geometries of downdrafts. By tracking the edges of the release we compare the dynamics of both the fall and the resulting gravity currents of our experimental data to that of previous results. In doing so we find that the resulting gravity current behaves like an axi-symmeteric finite release gravity current, whereas the fall doesnt seem to resemble anything previously studied. We hope that these results and future work will allow us to better inform forecasting of weather arising from such downdrafts. [Preview Abstract] |
Sunday, November 20, 2016 8:39AM - 8:52AM |
A10.00004: Experiments on horizontal convection at high Rayleigh and Prandtl numbers. Pierre-Yves Passaggia, Alberto Scotti, Brian White Horizontal convection is a flow driven by a differential buoyancy forcing across a horizontal surface. It has been considered as a simple model to study the influence of heating, cooling and fresh water fluxes at the ocean surface on the meridional overturning circulation. In order to investigate the flow properties and energetics of horizontal convection at high Prandtl numbers, the flow is driven by the diffusion of salt in water across membranes localized at the surface. The resulting experiments are examined for a Prandtl number $\rm{Pr}\approx 500$ and Rayleigh numbers up to $\rm{Ra}\approx10^{16}$. Time resolved particle image velocimetry is performed together with with planar laser induced fluorescence. To quantify the salt concentration and therefore the density of the fluid, sodium bisulfate is added to the salt water to decrease its pH of and thereby reduce the emission rate of the fluorescein dye. Rhodamine WT, insensitive to pH variations, is also introduced to correct for the spatial nonuniformity of the intensity of the laser sheet, a technique also known as ratiometric PLIF (Coppeta \& Rogers, 1998). The local turbulent energetics are finally investigated using the local approach to available potential energy of Scotti \& White (2014). [Preview Abstract] |
Sunday, November 20, 2016 8:52AM - 9:05AM |
A10.00005: Energetic dynamics of a rotating horizontal convection model of an ocean basin with wind forcing Varvara Zemskova, Brian White, Alberto Scotti We analyze the energetic dynamics in a rotating horizontal convection model, where flow is driven by a differential buoyancy forcing along a horizontal surface. This model is used to quantify the influence of surface heating and cooling and surface wind stress on the Meridional Overturning Circulation. We study a model of the Southern Ocean in a rectangular basin with surface cooling on one end (the South pole) and surface warming on the other end (mid-latitudes). Free-slip boundary conditions are imposed in the closed box, while zonally periodic boundary conditions are enforced in the reentrant channel. Wind stress and differential buoyancy forcing are applied at the top boundary. The problem is solved numerically using a 3D DNS model based on a finite-volume AMR solver [Santilli and Scotti, J. Comp. Phys, 2015] for the Boussinesq Navier-Stokes equations with rotation. The overall dynamics, including large-scale overturning, baroclinic eddying, turbulent mixing, and resulting energy cascades are investigated using the local Available Potential Energy framework introduced in [Scotti and White, J. Fluid Mech., 2014]. We study the relative contributions of surface buoyancy and wind forcing along with the effects of bottom topography to the energetic balance of this dynamic model. [Preview Abstract] |
Sunday, November 20, 2016 9:05AM - 9:18AM |
A10.00006: Modeling of quasi-constant volume gravity currents due to open-water sediment disposal Jenn Wei Er, Adrian Wing-Keung Law, E Eric Adams The near field transport of a sediment cloud in the water column after open-water disposal generally experiences two sequential phases: (i) convective descent phase, during which the cloud behavior is dominated by gravity, and (ii) bottom collapse phase, which upon impact the momentum and buoyancy of the cloud then drive the propagation along the seabed as a gravity current. The spreading of gravity current determines the zone of influence by the disposal event at the seabed. In this study, a modified Box-Model was proposed to assess the behavior of the gravity current. In particular, for the case of a split-barge, which is commonly used for land reclamation and contaminated sediment disposal, the model took into account the finite time period for the barge to fully discharge. Within this period, the sediments were continuously released from the barge, and supplied into the gravity current (as constant flux current). Beyond that, the gravity current continued to spread as a constant volume current instead. The interplay from constant flux to constant volume, which has significant implications on the engineering outcome, has not been addressed before. In addition, the modified Box-Model also included the geometry of the barge opening with a usual rectangular shape, generating differential spreading in both axes, and leading to the final elliptical zone of deposition. A laboratory study was carried out for model verification. The model predicted well the experimental results, while existing engineering models were inadequate due to their oversimplified representations. [Preview Abstract] |
Sunday, November 20, 2016 9:18AM - 9:31AM |
A10.00007: Clear salt water above sediment-laden fresh water: Interfacial instabilities Nathan Konopliv, Bartho Schulte, Eckart Meiburg The stability of an interface separating less dense, clear salt water above from more dense, sediment-laden fresh water below is explored via direct numerical simulations. We find that the destabilizing effects of double-diffusion and particle settling amplify each other above the diffusive interface, whereas they tend to cancel each other below. For moderate settling velocities, plumes form both above and below the interface, whereas for large settling velocities plume formation below the interface is suppressed. We identify the dimensionless parameter that determines in which regime a given flow takes place, along with the critical value at which the transition between the regimes takes place. [Preview Abstract] |
Sunday, November 20, 2016 9:31AM - 9:44AM |
A10.00008: Laboratory Experiments Modelling Sediment Transport by River Plumes Bruce Sutherland, Murray Gingras, Calla Knudson, Luke Steverango, Chris Surma Through lock-release laboratory experiments, the transport of particles by hypopycnal (surface) currents is examined as they flow into a uniform-density and a two-layer ambient fluid. In most cases the tank is tilted so that the current flows over a slope representing an idealization of a sediment-bearing river flowing into the ocean and passing over the continental shelf. When passing into a uniform-density ambient, the hypopycnal current slows and stops as particles rain out, carrying some of the light interstitial fluid with them. Rather than settling on the bottom, in many cases the descending particles accumulate to form a hyperpycnal (turbidity) current that flows downslope. This current then slows and stops as particles both rain out to the bottom and also rise again to the surface, carried upward by the light interstitial fluid. For a hypopycnal current flowing into a two-layer fluid, the current slows as particles rain out and accumulate at the interface of the two-layer ambient. Eventually these particles penetrate through the interface and settle to the bottom with no apparent formation of a hyperpycnal current. Analyses are performed to characterize the speed of the currents and stopping distances as they depend upon experiment parameters. [Preview Abstract] |
Sunday, November 20, 2016 9:44AM - 9:57AM |
A10.00009: Suspension-Driven Gravity Surges on Horizontal Surfaces: Effect of the Initial Shape. Nadim Zgheib, Thomas Bonometti, S. Balachandar We present results from fully-resolved direct numerical simulations of canonical (axisymmetric and planar) and non-canonical (rectangular) configurations of horizontal suspension-driven gravity surges. We show that the dynamics along the initial minor and major axis of a rectangular release are roughly similar to that of a planar and axisymmetric current, respectively. However, contrary to expectation, we observe under certain conditions the final extent of the deposit from finite releases to surpass that from an equivalent planar current. This is attributed to a converging flow of the particle-laden mixture towards the initial minor axis, a behaviour that was previously reported for scalar-driven currents on uniform slopes. This flow is observed to be correlated with the travelling of a perturbation wave generated at the extremity of the longest side that reaches the front of the shortest side in a finite time. A semi-empirical explicit expression (based on established relations for planar and axisymmetric currents) is proposed to predict the extent of the deposit in the entire x-y plane. Finally we observe that for the same initial volume of a suspension-driven gravity surge, a release of larger initial horizontal aspect-ratio is able to retain particles in suspension for longer periods of time. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700