Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session F34: Convection and Buoyancy-driven Flows: General II |
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Chair: Laurence Rongy, University Libre De Brussels Room: Georgia World Congress Center B406 |
Monday, November 19, 2018 8:00AM - 8:13AM |
F34.00001: A Projection Method for Solid-Liquid Phase Transitions with Natural Convection Olav Rømcke, R. Jason Hearst A projection method for solving convection dominated solid-liquid phase transitions on a fixed, Cartesian, staggered grid is presented. A melting cavity case has been simulated and compared to an experimental study of pure gallium. The difference between a 3D and a 2D simulation is highlighted here. In addition, an attempt was made at finding a non-dimensional group that correlated well with the global liquid fraction. Finally, simulations of two mould-melt casting geometries with and without convective energy transport highlights the effect of the convective currents. |
Monday, November 19, 2018 8:13AM - 8:26AM |
F34.00002: Rayleigh-Bénard convection interacting with a melting boundary Jhaswantsing Purseed, Benjamin Favier, Laurent Duchemin We study the evolution of a melting front between the solid and liquid phases of a pure incompressible material where fluid motion is driven by unstable temperature gradients. In a plane layer geometry, this can be seen as classical Rayleigh-Bénard convection, where the upper solid boundary is allowed to melt due to the heat flux brought by the fluid underneath. This free-boundary problem is studied numerically in two dimensions using a phase-field approach, which we dynamically couple with the Navier--Stokes equations under the Boussinesq approximation. We focus on the case where the solid is initially nearly isothermal, so that the evolution of the topography is related to the inhomogeneous heat flux from thermal convection, and does not depend on the conduction problem in the solid. From a very thin stable layer of fluid, convection cells appear as the depth (and therefore the Rayleigh number) of the layer increases. In the supercritical regime, the continuous melting of the solid leads to dynamical transitions between different convective cell sizes and topography amplitudes. The Nusselt number can be larger than its reference value for a flat upper boundary due to the feedback of the topography on the flow, which can stabilize large-scale laminar convective cells. |
Monday, November 19, 2018 8:26AM - 8:39AM |
F34.00003: Modeling of Ablation on an Irradiated Target Igbal Mehmedagic, Sivag Thangam Modeling of constant and pulsed irradiation on metallic targets is presented. The model formulation involves ablation of the metallic target irradiated by both constant and pulsed high intensity laser at normal atmospheric conditions. Computational findings based on effective representation of the melting and vaporization of the targeting material as well as plume formation and expansion are presented. In this context, the available results for representative irradiation from constant and pulsed laser pulse on aluminum and steel targets are used to analyze various ablation mechanisms, variable thermo-physical and optical properties, plume expansion and surface geometry. The relevance of the findings for the development of protective shields is discussed. |
Monday, November 19, 2018 8:39AM - 8:52AM |
F34.00004: On the use of air curtains to control smoke spread in an enclosed fire Nigel Berkeley Kaye, Nicholas J Williamson, Steven Armfield We present results of a series of experiments in which a planer vertical turbulent jet (model air curtain) was used to confine the outflow from a round turbulent plume (model fire). Salt bath experiments using the light attenuation technique were used to measure the stratification that formed either side of the planar jet. The tests were configured such that the jet and plume both flowed in the same direction. When the plume was first started it flowed to the base of the tank and formed an outflow which slowly filled the region of the tank on the plume side of the planar jet with a dense salty layer. Some of this dense layer was entrained into the planar jet and was transferred to the other section of the enclosure. The developing stratification on the plume side of the jet eventually pushed the jet over and a large scale transfer of salty water across the jet ensued. A model is presented that uses a simplified filling box theory and a modified air curtain deflection modulus to predict the time at which the jet no longer constrains the stratification. |
Monday, November 19, 2018 8:52AM - 9:05AM |
F34.00005: Comparison of local hat transfer distribution between closed and open cavity for different Rayleigh number and inclination angles Ashish Saxena, Suneet Singh, Atul Srivastava The numerical analysis of heat transfers and flow patterns in a closed cubic cavity for different combinations of Rayleigh number and inclination angles has been considered in the present study. From the literature, it is observed that several studies have been carried out in the parlance of convective heat transfer in closed as well as in open cavities. The main objective of the earlier studies was to capture the variation in average Nusselt number with different influencing parameters. However, the present study is concerned with the comparisons of the patterns of heat transfer distribution at the hot wall between closed and open cavities for different combinations of Rayleigh numbers and inclinations. From the present study, it is interesting to note that, at 90° inclination results have similar patterns of the heat transfer distribution for all the values of Rayleigh numbers even though these cases have quite large difference in average Nusselt numbers. While at 30° inclination, significant differences in the heat transfer patterns is observed in closed cavity compared to that of the corresponding open cavity. The plausible reason for getting this difference, the vortex flow, stream ribbons and the isotherms have also been studied at different surfaces of the cavity. |
Monday, November 19, 2018 9:05AM - 9:18AM |
F34.00006: Effect of mainstream flow oscillations on the spatial and temporal variations of film cooling Wenwu Zhou, Di Peng, Xin Wen, Yingzheng Liu The influence of mainstream oscillations on the spatio-temporal variation of film cooling were quantified extensively by the fast-response pressure-sensitive paint (fast-PSP) technique. During the experiment, coolant was discharged from a 35°-inclined round hole and injected into the cross flow. While the steady state (i.e., f = 0 Hz) was selected as the baseline, the freestream oscillating frequency were increased from 5 Hz to as high as 20 Hz. Measured instantaneous effectiveness results were analyzed in terms of the ensemble-averaged and phase-averaged methods, where the latter one was acquired through triple decomposition. Compared to the steady state, a reduction of 30–35% was observed for the ensemble-averaged results at f = 20 Hz cases. As for the phase-averaged results, a relatively weak dependence was observed at 5 Hz with respect to the phase angles. However, as the frequency increased to 20 Hz, obtained effectiveness exhibited a strong correlation with the velocity phase. In general, mainstream oscillations have a significant impact on the film cooling behavior. They not only degrade the cooling effectiveness, but also increase the unsteadiness in film cooling. |
Monday, November 19, 2018 9:18AM - 9:31AM |
F34.00007: Large-scale circulation in Rayleigh-B\'{e}nard convection with a Prandtl number 12.3$^*$ Ping Wei
\vskip 0.02in \noindent $^*$Measurements were made in collaboration with G. Ahlers at UCSB.
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Monday, November 19, 2018 9:31AM - 9:44AM |
F34.00008: Line plumes in a filling box R. Akhter, J. D. Compton, Nigel Kaye Results are presented from a series of experiments that measured the stratification formed by a line plume that spans the full width of a rectangular enclosure. Experiments were run with the line plume centered in the enclosure, against one wall, and at several intermediate locations. The light attenuation technique was used to track the stratification that developed on either side of the plume. When the plume was centered the flow was symmetric and the stratification was well described by the standard filling box model. When the plume source was placed adjacent to a wall it attached to the wall so that there was only one developing stratification. When the plume was asymmetrically located the front position on either side of the plume was also asymmetric. Further, after the initial outflow had reached the end wall and the first fronts had formed on either side of the plume, the plume was strongly deflected toward the closest wall even though that side had a thicker dense layer such that there was a net hydrostatic pressure force driving the plume in the other direction. Our experimental results are compared to a modified filling-box model. |
Monday, November 19, 2018 9:44AM - 9:57AM |
F34.00009: Oscillatory flow induced by the coupling between Marangoni and buoyancy-driven convection in a reactive system Virat Upadhyay, Marcello Antonio Budroni, Laurence Rongy When two reactants A and B, initially separated in space, react upon diffusive mixing, the product C can generate connective flows by locally changing the surface tension of the solution or its density. |
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