Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session R10: Convection and Buoyancy-Driven Flows: General |
Hide Abstracts |
Chair: Daria Frank, University of Cambridge Room: 110 |
Tuesday, November 24, 2015 12:50PM - 1:03PM |
R10.00001: Aerodynamical sealing by air curtains Daria Frank, Paul Linden Air curtains are artificial high-velocity plane turbulent jets which are installed in a doorway in order to reduce the heat and the mass exchange between two environments. The performance of an air curtain is assessed in terms of the sealing effectiveness $E$, the fraction of the exchange flow prevented by the air curtain compared to the open-door situation. The main controlling parameter for air curtain dynamics is the deflection modulus $D_m$ representing the ratio of the momentum flux of the air curtain and the transverse forces acting on it due to the stack effect. In this talk, we examine the influence of two factors on the performance of an air curtain: the presence of an additional ventilation pathway in the room, such as a small top opening, and the effects of an opposing buoyancy force which for example arises if a downwards blowing air curtain is heated. Small-scale experiments were conducted to investigate the $E(D_m)$-curve of an air curtain in both situations. We present both experimental results and theoretical explanations for our observations. We also briefly illustrate how simplified models developed for air curtains can be used for more complex phenomena such as the effects of wind blowing around a model building on the ventilation rates through the openings. [Preview Abstract] |
Tuesday, November 24, 2015 1:03PM - 1:16PM |
R10.00002: Thermal Convection on an Ablating Target Igbal Mehmedagic, Siva Thangam Modeling and analysis of thermal convection of a metallic targets subject to radiative flux is of relevance to various manufacturing processes as well as for the development of protective shields. The present work involves the computational modeling of metallic targets subject to high heat fluxes that are both steady and pulsed. Modeling of the ablation and associated fluid dynamics when metallic surfaces are exposed to high intensity pulsed laser fluence at normal atmospheric conditions is considered. The incident energy from the laser is partly absorbed and partly reflected by the surface during ablation and subsequent vaporization of the convecting melt also participates in the radiative exchange. The energy distribution during the process between the bulk and vapor phase strongly depends on optical and thermodynamic properties of the irradiated material, radiation wavelength, and laser pulse intensity and duration. Computational findings based on effective representation and prediction of the heat transfer, melting and vaporization of the targeting material as well as plume formation and expansion are presented and discussed in the context of various ablation mechanisms, variable thermo-physical and optical properties, plume expansion and surface geometry. [Preview Abstract] |
Tuesday, November 24, 2015 1:16PM - 1:29PM |
R10.00003: Collective motion of multiple rafts on the Rayleigh-Benard convection Fahrudin Nugroho, Dewi Lita Martanti, Ryan Pratama, Agung Bambang S.U., Pekik Nurwantoro, Dian Artha K We observe the dynamics of rafts on the Rayleigh-Benard convection. A single raft motion shows at least three types of motions i.e. the linear, oscillatory, and random motions. The velocity of single raft fits with the gaussian distribution function. While the multiple rafts case show more complex motion, including the possibility of collective motion. We show that there is an indication of collective motion of multiple rafts as one of the law of motion in the Rayleigh-Benard convection. [Preview Abstract] |
Tuesday, November 24, 2015 1:29PM - 1:42PM |
R10.00004: Mixing and Displacement Buoyancy-Driven Exchange Flow Between Adjacent Zones Saleh Nabi, Morris Flynn Buoyancy driven flow between two finite zones containing fluid of slightly different density is investigated. The two zones are separated by either a single common doorway or top and bottom vents. In the former case, a two-layer exchange flow develops once the barrier is removed. A buoyant plume of light fluid mixes with the dense fluid leading, over time, to the development of non-trivial ambient density stratification. Meanwhile, a gravity current propagates into the light zone, which upon reflection and reaching the doorway in a form of an internal bore, alters the dynamics of the exchange flow. The exchange flow is also significantly altered if and when the first front in the dense zone falls below the top of the doorway, in which case an intermediate layer develops in the light zone. Conversely, when the two zones are separated by top and bottom vents, two oppositely directed exchange flows are generated. The transient evolution of the interface, stratification and buoyancy in each zone are estimated both for the case where the light zone does and does not contain a source of buoyancy. Similitude experiments help to identify the limitations of the analytical models for each scenario. [Preview Abstract] |
Tuesday, November 24, 2015 1:42PM - 1:55PM |
R10.00005: Influence of mushy zone constant on the solid-liquid phase change process modeled by enthalpy-porosity technique Saeed Tiari, Mahboobe Mahdavi, Songgang Qiu In the present work, the effects of mushy zone constant on the melting and solidification processes simulation with enthalpy-porosity technique are investigated. The isothermal melting and solidification of gallium enclosed by a rectangular container is studied using a transient two-dimensional finite volume based model. A wide range of mushy zone constants are considered in the study of the thermal and fluid flow characteristics of the system. The results indicate that increasing the mushy zone constant value up to a limit leads to the acceleration of the solidification process, while it decreases the melting rate. However, the further increase of the constant does not affect the phase change process in melting and solidification. It is found that the mushy zone constant has a significant influence on the temperature distribution adjacent to the melt front as well as the morphology of the solid-liquid interface. This is due to the effect of mushy zone constant on the flow in the mushy region and liquid layers nearby. The results also reveal that the increase of mushy zone constant results in the decrease of average wall heat flux in both melting and solidification processes. [Preview Abstract] |
Tuesday, November 24, 2015 1:55PM - 2:08PM |
R10.00006: Coolant Design System for Liquid Propellant Aerospike Engines Miranda McConnell, Richard Branam Liquid propellant rocket engines burn at incredibly high temperatures making it difficult to design an effective coolant system. These particular engines prove to be extremely useful by powering the rocket with a variable thrust that is ideal for space travel. When combined with aerospike engine nozzles, which provide maximum thrust efficiency, this class of rockets offers a promising future for rocketry. In order to troubleshoot the problems that high combustion chamber temperatures pose, this research took a computational approach to heat analysis. Chambers milled into the combustion chamber walls, lined by a copper cover, were tested for their efficiency in cooling the hot copper wall. Various aspect ratios and coolants were explored for the maximum wall temperature by developing our own MATLAB code. The code uses a nodal temperature analysis with conduction and convection equations and assumes no internal heat generation. This heat transfer research will show oxygen is a better coolant than water, and higher aspect ratios are less efficient at cooling. [Preview Abstract] |
Tuesday, November 24, 2015 2:08PM - 2:21PM |
R10.00007: Bounds on heat transport in Rayleigh's and related models of B\'enard convection Charles R. Doering, Andre N. Souza, Baole Wen, Gregory P. Chini, Richard R. Kerswell We present new upper limits on convective heat transport in both the full and several low-dimensional Galerkin truncations of Rayleigh's 1916 model of buoyancy-driven B\'enard convection using both the so-called background method as well as optimal control variational techniques. [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