Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session L2: Convection and Buoyancy-Driven Flows V: Binary Systems and Stratified Flows |
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Chair: Edgar Knobloch, University of California, Berkeley Room: 324 |
Monday, November 25, 2013 3:35PM - 3:48PM |
L2.00001: Thermal Stratification by Steam Condensation of RCIC in Suppression Pool Koji Okamoto, Daehun Song, Nejdet Erkan In Fukushima-Daiichi NPP accident, the RCIC operated more than a couple of days. The steam condensation at the supression pool may cause the thermal-stratification. The phenomena may affects on the capacity of RCIC and also the progression of the event in case of Severe Accident. To investigate the mechanism of formation of thermal stratification and the effects in suppression pool, down-sized SP model was designed and time resolved temperature and pressure data were acquired. During the experiments well-established stationary thermal stratification was detected since the start of steam injection. PIV was carried out to figure out the natural circulation due to the buoyancy and the mixing interface, which decides the pressure suppression capacity of suppression pool (SP). Numerical simulation was carried out with ANSYS CFX 14.0 in single phase and validated with experimental data. [Preview Abstract] |
Monday, November 25, 2013 3:48PM - 4:01PM |
L2.00002: Chemical control of hydrodynamic instabilities in partially miscible two-layer systems A. De Wit, L.A. Riolfo, L. Lemaigre, F. Rossi, M. Rustici, M.A. Budroni Hydrodynamic instabilities at the interface between two partially miscible liquids impact numerous applications including sequestration of supercritical liquid CO$_2$ in old petroleum reservoirs or saline aquifers. As an alternative to difficult {\it in situ} studies of the related mixing dynamics, we introduce a new laboratory-scale model system on which buoyancy- and Marangoni-driven convective instabilities of partially miscible two-layer systems can easily be studied and controlled in presence or not of chemical reactions. This system consists in the stratification of a pure ester on top of a denser partially miscible aqueous solution in the gravitational field. The rich convective dynamics observed upon partial dissolution of the ester in the water followed by its hydrolysis highlight the specificity of partially miscible systems as compared to fully miscible or immiscible ones, i.e. the possibility to control the convective pattern and the mixing properties by tuning (i) the intrinsic miscibility of the ester in water, (ii) the feedback of the dissolved species on its own miscibility as well as (iii) the composition and reactivity of the aqueous solution with the ester phase. [Preview Abstract] |
Monday, November 25, 2013 4:01PM - 4:14PM |
L2.00003: Convective dissolution of carbon dioxide in salted water: linear stability analysis and effect of control parameters Vanessa Loodts, Laurence Rongy, Anne De Wit We study the convective dissolution of carbon dioxide ($\rm CO_2$) in salted water theoretically. We perform a linear stability analysis with regard to buoyancy-driven convection of the time-dependent concentration profiles of $\rm CO_2$ diffusing into the aqueous solution. On the basis of a parameter-free dimensionless model, we predict the time of onset and wavenumber of the instability when the system becomes unstable, i.e. when the growth rate of the instability equals zero. We also define a characteristic growth rate $\sigma^*$ quantifying the growth of the perturbations in the unstable regime. We find good agreement of $\sigma^*$ with growth rates of buoyancy-driven fingering available in the literature. We moreover explicit the procedure to compare the dimensionless theoretical prediction with dimensional experimental and numerical data and analyze the influence of parameters controlling implicitly the characteristic length and time scales of the problem. We find that increasing the partial pressure of $\rm CO_2$, or decreasing the aqueous salt concentration or the temperature destabilize the system, leading to faster growing buoyancy-driven fingers. [Preview Abstract] |
Monday, November 25, 2013 4:14PM - 4:27PM |
L2.00004: Convection in binary fluids with phase change: solutocapillarity, thermocapillarity and buoyancy Yaofa Li, Minami Yoda Evaporative cooling is of interest in thermal management applications. In most cases, thermocapillary stresses drive liquid coolant away from hot regions, adversely affecting performance. Volatile binary fluids can, however, be tailored with \textit{solutocapillary }stresses that drive liquid instead towards hot regions. Although such binary-fluid coolants could improve the cooling performance of devices such as heat pipes, convection in a binary fluid subject to phase change, especially in a confined geometry in the (near-)absence of noncondensables as is the case in heat pipes, is poorly understood. Capillary-buoyancy convection in liquid layers (with depths of a few mm) driven by temperature differences as great as 10 $^\circ$C over a horizontal distance of 4.9 cm was therefore studied with particle-image velocimetry (PIV). The flow of water-methanol mixtures (with methanol fractions as great as 60{\%}) was studied under conditions where the vapor space was filled with ambient air, and a mixture of water and methanol vapor with a small amount of air. The results show that varying the amount of air in the vapor space has a marked effect on the flow in the liquid layer. [Preview Abstract] |
Monday, November 25, 2013 4:27PM - 4:40PM |
L2.00005: Compositional transport in solidifying aqueous binary solution Jin-Qiang Zhong, Zuo-Chao Yin, Qiwei Xue, John Wettlaufer We observe the formation of double-diffusive layers adjacent to mushy layers that form during the directional solidification of aqueous ammonium chloride. The plumes emerging from chimney's in the mushy layers continuously supply a buoyancy flux in the (finite) liquid region above, driving downward motion of double-diffusive layers. The downward velocity of the layers is found to be in good agreement with a filling box model that captures the crucial hydrodynamics of the entraining buoyant plumes and compositional transport. We demonstrate that the buoyancy flux through the system decays according to a similarity solution. We note that the experimental findings provide some insight into the brine transport in growing sea ice. [Preview Abstract] |
Monday, November 25, 2013 4:40PM - 4:53PM |
L2.00006: Colliding Convectons Edgar Knobloch, Isabel Mercader, Oriol Batiste, Arantxa Alonso Convectons are strongly nonlinear spatially localized states found in thermally driven fluid flows. In systems with midplane reflection symmetry stationary convectons of odd and even parity lie on a pair of intertwined branches that form the backbone of the snakes-and-ladders structure of a ``pinning'' region in parameter space (Mercader et al., J. Fluid Mech. 667 (2011) 586). When the midplane reflection symmetry is broken, the odd parity convectons start to drift with a speed that depends on the magnitude of the symmetry-breaking and the convecton length. Direct numerical simulations are used to study head-on and follow-on collisions between such drifting convectons in binary fluid convection, and the results compared and contrasted with corresponding dynamics in a Swift-Hohenberg model studied by Houghton and Knobloch (PRE 84 (2011) 016204). In contrast to completely integrable systems the collisions are strongly inelastic (Mercader et al., J. Fluid Mech. 722 (2013) 240). [Preview Abstract] |
Monday, November 25, 2013 4:53PM - 5:06PM |
L2.00007: Accuracy of the 2D+$t$ Approximation for Turbulent Wakes in Stratified Flows Laura Pauley Wakes in the ocean can be produced by a stationary object in a current or by a moving object in stationary water. When viewed in a reference frame moving with the object, the wake can persist thousands of object diameters downstream. Due to the extensive domain, an unsteady two-dimensional (2D+$t$) computation is often used to sweep downstream through the wake development. The 2D+$t$ computation approximates the development of the wake at a fixed location as an object moves past but applies cyclical boundary conditions in the streamwise direction. A Parabolized Navier-Stokes (PNS) method has the same numerical efficiency as the 2D+$t$ method but includes additional streamwise gradient terms found in the three-dimensional governing equations. The present paper investigates the accuracy of the 2D+$t$ approximation for stratified turbulent wake flows for a range of Froude numbers and Reynolds numbers. The 2D+$t$ results are compared with results from 3D Navier-Stokes computations and results from PNS computations to identify criteria at which the 2D+$t$ method will yield accurate results. [Preview Abstract] |
Monday, November 25, 2013 5:06PM - 5:19PM |
L2.00008: Large eddy simulation of buoyancy induced asymmetry in horizontal jets Niranjan Ghaisas, Steven Frankel Horizontal injection of a heavier fluid into a lighter ambient leads to a horizontal buoyant jet. This configuration is marked by the simultaneous presence of stable stratification above the jet centerline, and unstable stratification below it. This leads to unequal rates of turbulent mixing and an asymmetric development of the jet above and below the centerline. This asymmetry between the stably stratified and unstably stratified regions in the horizontal jet is investigated using large eddy simulations in this study. Parameters such as radial half-widths and measures of anisotropy are investigated. Differences in the structures occurring in stable and unstable stratifications are pointed out. Finally, a dynamic mode decomposition analysis is performed with the stably stratified and unstably stratified regions considered together, as well as individually. It is seen that the unstably stratified region is more energetic, and prone to instabilities, as compared to the stably stratified region. [Preview Abstract] |
Monday, November 25, 2013 5:19PM - 5:32PM |
L2.00009: A periodic mixing mechanism in stratified turbulent Taylor-Couette flow Rosalind Oglethorpe, C.P. Caulfield, Andrew W. Woods We present results from a series of laboratory experiments to study the mixing mechanism in two-layer, stratified turbulent Taylor-Couette flow. We focus on the case of strong stratification, where the density difference $\Delta\rho$ is sufficiently high that the vertical buoyancy flux across the interface is constant (as found by Woods {\it et al.} (2010){\it JFM}{\bf 663} and Oglethorpe {\it et al.} (2013){\it JFM}{\bf 721}). We vary the radius, $R_{1}$, surface roughness and rotation rate, $\Omega$, of the inner cylinder, relative to the stationary outer cylinder, of radius $R_{2}$. The measurements of the density field near the interface, using both conductivity probe data and visualization techniques, show a periodic signal which is associated with the mixing. We find that the period of the signal is given by $T \propto (2\pi/\Omega)(R_{2}/R_{1})$. We also find that the mean angular momentum in the bulk of the flow is constant, and depends on the surface roughness of the inner cylinder. We use these results to present an interpretation of the mixing mechanism related to the periodic signal. [Preview Abstract] |
Monday, November 25, 2013 5:32PM - 5:45PM |
L2.00010: Flows and Stratification of an Enclosure Containing Both Localised and Vertically Distributed Sources of Buoyancy Jamie Partridge, Paul Linden We examine the flows and stratification established in a naturally ventilated enclosure containing both a localised and vertically distributed source of buoyancy. The enclosure is ventilated through upper and lower openings which connect the space to an external ambient. Small scale laboratory experiments were carried out with water as the working medium and buoyancy being driven directly by temperature differences. A point source plume gave localised heating while the distributed source was driven by a controllable heater mat located in the side wall of the enclosure. The transient temperatures, as well as steady state temperature profiles, were recorded and are reported here. The temperature profiles inside the enclosure were found to be dependent on the effective opening area $A^*$, a combination of the upper and lower openings, and the ratio of buoyancy fluxes from the distributed and localised source $\Psi=\frac{B_w}{B_p}$. [Preview Abstract] |
Monday, November 25, 2013 5:45PM - 5:58PM |
L2.00011: The Radial Spreading of Intrusions Originating from a Plume in Stratified Fluid Tamar Richards, Quentin Aubourg, Bruce Sutherland Supervolcanoes send a plume of hot particle-laden air into the stratosphere where it eventually falls back upon itself as a fountain and then spreads laterally at its neutral buoyancy level. In order to gain insight into the initial spreading of such intrusions, we have performed laboratory experiments of fresh water injected downward through a turbulent plume nozzle into a uniformly stratified fluid. Though neglecting the influence of particles and anelastic effects, the experiment provides insight into the dynamics of radially spreading intrusions in the buoyancy-inertia regime within the Boussinesq approximation. Our theoretical and experimental results extend the prediction of Bloomfield and Kerr (JFM 1998,2000) to predict the spreading height as a function of the source momentum, buoyancy and ambient stratification for buoyancy- as well as momentum-driven sources. We find the radius of the front increases as a power law with approximately $3/4$ exponent, different from self-similarity theory, which predicts a $2/3$ exponent. Nonetheless, the intrusion structure adopts a self-similar shape with scaled height as a function of scaled radius having an approximate $1/2$ power law from nose to tail. [Preview Abstract] |
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