Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session L2: Convection and Buoyancy-Driven Flows VI: Plumes |
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Chair: Andrew Wells, University of Oxford Room: 23A |
Monday, November 19, 2012 3:35PM - 3:48PM |
L2.00001: Collapsing plumes and resurrecting fountains Ton van den Bremer, Gary Hunt We explore the range of behaviour predicted for steady plumes and fountains that undergo an increase or decrease in buoyancy which arise due to phase changes or chemical reactions. We model these changes in the simplest possible way by assuming a quadratic relationship between the density and the temperature of the fluid. We thereby extend the model of Caulfield \& Woods~(`95) to include the most recent developments in the literature on steady releases of buoyancy emitted vertically from horizontal area sources in unconfined quiescent environments of uniform density based on the plume model of Morton, Taylor \& Turner~(`56). We provide closed-form solutions and identify four classes of solution: collapsing plumes, resurrecting fountains, plumes with enhanced buoyancy and fountains with enhanced negative buoyancy. We provide criteria for each category of behaviour in terms of the source-value of two non-dimensional quantities: the Richardson number and a temperature parameter.\\[4pt] Caulfield, C. C. P. \& Woods, A. W. 1995. Plumes with non-monotonic mixing behaviour. Geophys. Astro. Fluid. \textbf{79}, 1-4, 173-199. Morton, B.R., Taylor, G.I. \& Turner, J.S. 1956. Turbulent gravitational convection from maintained and instantaneous sources. Proc. Roy. Soc. Lond. A \textbf{234}, 1-23. [Preview Abstract] |
Monday, November 19, 2012 3:48PM - 4:01PM |
L2.00002: ABSTRACT WITHDRAWN |
Monday, November 19, 2012 4:01PM - 4:14PM |
L2.00003: A Comparison of Single and Multiphase Turbulent Jets, Pure and Forced Plumes at Moderate Reynolds Numbers. G.N. Taub, S. Balachandar, F. Plourde Turbulent axisymmetric shear flows, such as jets and plumes arise often in industrial applications and environmental studies. The recent Deep Water Horizon oil spill in the Gulf of Mexico is one example which brought to light the need for a greater understanding of the turbulent behavior of such flows. The results of Direct Numerical Simulations of single phase pure jets (Re=2000), pure plumes (Gr = 2000$^{2})$ and forced plumes (Re=1684, Ri=0.025), where both buoyancy and initial momentum are present, will be compared and contrasted. In addition to the mean flow behavior, second and third order statistics will be presented as well as the turbulent energy balance for all three flows. In the case of the forced plume, the transition from jet like behavior near the source of initial momentum to plume like behavior in the far field will be discussed. Preliminary results of laboratory experiments and Direct Numerical Simulations of multiphase forced plumes will also be presented. [Preview Abstract] |
Monday, November 19, 2012 4:14PM - 4:27PM |
L2.00004: Instability of plumes driven by localized heating Francisco Marques, Juan M. Lopez, Younghae Do Plumes due to localized buoyancy sources are of wide interest due to their prevalence in many situations, including fires, chimneys, volcanoes, deep sea hydrothermal vents and a wide variety of other atmospheric and oceanic situations. In this study, we are interested in the transition from laminar to turbulent plumes. In experiments, this transition is found to be sensitive to external perturbations. Therefore a well-controlled set-up has been chosen: a localized heat source at the bottom of an enclosed cylindrical container, at a uniform temperature except for the heat source. At moderate Rayleigh numbers Ra, the flow consists of a plume, which is steady, axisymmetric and purely poloidal. By increasing Ra, the flow undergoes a supercritical Hopf bifurcation at Ra~3.8E7, to an axisymmetric ``puffing'' plume, that becomes unstable to three-dimensional disturbances at about Ra~5.4E7. At larger Ra $>$ 1.E8, the plume becomes chaotic via a torus-breakup bifurcation. [Preview Abstract] |
Monday, November 19, 2012 4:27PM - 4:40PM |
L2.00005: Laminar plume formation by high pressure CO2 Francois Nadal, Patrice Meunier, Bernard Pouligny, Eric Laurichesse Convection flows have often revealed the presence of plumes, especially in the earth's mantle where the Schmidt number is large. There has thus been a large number of studies on plumes created by a point source. However, there are very few results on plumes generated by an extended source. Here, we present experimental, numerical and theoretical results on the flow created by high pressure CO2 dissolved into distilled water. The thin layer of dense fluid created at the surface destabilizes through the Rayleigh-Taylor instability and leads to a laminar and parallel stationary plume. The plume width and amplitude are measured by Particle Image Velocimetry for various aspect ratios, Bond and Rayleigh numbers. They are in good agreement with the numerical result if a no-slip boundary condition is assumed at the free surface. Finally, the theory for a plume generated by a point source is adapted for an extended source, which leads to different scaling exponents (with a logarithmic dependence), in excellent agreement with the experimental and numerical results. This study thus provides a simple and accurate description of axisymmetric plumes generated by an extended source. [Preview Abstract] |
Monday, November 19, 2012 4:40PM - 4:53PM |
L2.00006: Self-similarity of Boussinesq Miscible Thermals: an Experimental Study Bing Zhao, Adrian Lai, Adrian Law, Eric Adams The gross characteristics of fully-developed round miscible thermals have been well studied and reported to be self-similar (e.g. Scorer, 1957). However, there have been very few studies (Bond {\&} Johari, 2005; Hart, 2008) concerning the internal structures of the thermal. Many important questions related to the interior fluid dynamics inside the thermal, including the self-similarity of the internal velocity and scalar distributions, remain outstanding. In the present study, detailed PIV and PLIF measurements were conducted in the axisymmetric plane (i.e. side view) of a negatively buoyant Boussinesq thermal to reveal the detailed internal structures, with CCD cameras that synchronized with a unique release mechanism that minimized the initial variations. Synchronized simultaneous flow visualization (with spotlights and a video camera) were also made to monitor the developmental shape of the thermal through a bottom view. The simultaneous information enabled an objective assessment of the experimental quality. The results showed that the maximum radius of the miscible thermal grows linearly with travel distance, which agrees with previous studies using dimensional analysis with self-similarity. The radius of the vortex ring is found to be expanding linearly, but surprising at a smaller growth rate that the overall thermal size. This raises a critical question whether the self-similarity with thermals truly exists or not. The results will be presented at the meeting. [Preview Abstract] |
Monday, November 19, 2012 4:53PM - 5:06PM |
L2.00007: The velocity field of laboratory fire whirls Katherine Hartl, Stacy Guo, Alexander Smits Fire whirls increase the intensity of wild fires, and they enhance the spreading rate of fire by ejecting flaming debris, often rendering prepared fire fighting plans useless. Fire whirls are produced by buoyancy, ambient vorticity, and the titling of regions of intense horizontal negative shear at the fire front. They can shed from a smoke plume, form in the turbulent wake of a hill, or arise due to concentrated heat sources. To understand and model fire whirls in greater detail, an experimental study is conducted to generate a fire whirl in the laboratory, and examine the velocity fields outside and inside the vortex core. We use flow visualization and PIV to obtain qualitative and quantitative data, and discuss the scaling behavior. [Preview Abstract] |
Monday, November 19, 2012 5:06PM - 5:19PM |
L2.00008: Laboratory-Scale Simulation of Spiral Plumes in the Mantle. Albert Sharifulin, Anatoly Poludnitsin On the basis of laboratory simulation a mechanism is established for the formation of the upper mantle convection spiral plumes from acore hot point in the presence of a roll-type large-scale convective flow. The observed plume has horizontal sections near the upper limit of cavity, which may lead to the formation of chains of volcanic islands. We experimentally simulated the appearance of a plume from the hot by green laser generated hot spot and study its interaction with cellular flow, simulating beneath the plates shear flow. It is shown that the presence of cellular convective motion may lead to the formation of a strange spiral convective plume. Experimentaly showed that the presence of cellular convective motion (simulating the large-scale shear flow exists beneath the plates) the plume from a point source of heat (core hot point) can acquire a spiral shape with horizontal sections needed to launch the mechanism of formation of chains of volcanic islands [1].\\[4pt] [1] Skilbeck, J. N.; Whitehead, J. A. (1978). Formation of discrete islands in linear chains. Nature \textbf{272}: 499--501. http://en.wikipedia.org/wiki/Nature\_(journal) [Preview Abstract] |
Monday, November 19, 2012 5:19PM - 5:32PM |
L2.00009: Meltwater-plume dynamics under an evolving ice shelf Andrew Wells Recent observations and models suggest that melting at the base of floating ice shelves can significantly impact ice sheet flow, with consequences for sea level rise. As a simplified analogue of ice-shelf basal melting, I consider a theoretical model of the melting of a two-dimensional stationary ice-shelf above a warmer glacial ocean. Melting rates are controlled by a turbulent buoyancy-driven plume of meltwater that is coupled to an ice-water free boundary that evolves as a result of melting. The evolving slope of the ice-shelf base provides a feedback on flow and heat transfer in the meltwater plume, with potential consequences for the stability of ice shelves and other systems featuring a coupling of melting and buoyancy-driven flow. [Preview Abstract] |
Monday, November 19, 2012 5:32PM - 5:45PM |
L2.00010: Generation of gravity waves by convective plumes Michael Le Bars, Stephane Perrard, Peter Huck, Adrien Aubert, Patrice Le Gal In many geo- and astrophysical situations, a turbulent convective fluid layer is separated from a stably stratified one by a relatively sharp but deformable interface. Examples include the oceanic upper mixed layer and underlying pycnocline zone, the convective and radiative zones in stars, the atmospheric convective layer and overlying stratosphere. Here we present 2 experimental studies to get a global description of the properties of the excited wave field and its interaction with the convective motions. In the first set-up, a turbulent plume generated by injection of water impinges upon the interface between a uniform density layer and a linearly stratified one of salted water. In the second set-up, we take benefit from the unusual property of water that its density has a maximum value near 4$^{\circ}$C to study its convective and oscillatory motions in a tank with a bottom boundary at about 0$^{\circ}$C and an hotter upper surface. In both experiments, the velocity fields are measured non-intrusively using PIV, allowing to determine the energy flux extracted from the plume and transported by the waves. The spectral analysis of the signals exhibit preferred values of the frequency and wavelength of excited waves which depend on the location. Those results compare well with a simple analytical approach where the impinging plume is modeled as a initial displacement of the interface with a Gaussian shape in time and space. [Preview Abstract] |
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