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  • 1
    Electronic Resource
    Electronic Resource
    THE FLUID MECHANICS OF NATURAL VENTILATION (1999)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Fluid Mechanics 31 (1999), S. 201-238 
    Details
    ISSN: 0066-4189
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Natural ventilation of buildings is the flow generated by temperature differences and by the wind. The governing feature of this flow is the exchange between an interior space and the external ambient. Although the wind may often appear to be the dominant driving mechanism, in many circumstances temperature variations play a controlling feature on the ventilation since the directional buoyancy force has a large influence on the flow patterns within the space and on the nature of the exchange with the outside. Two forms of ventilation are discussed: mixing ventilation, in which the interior is at an approximately uniform temperature, and displacement ventilation, where there is strong internal stratification. The dynamics of these buoyancy-driven flows are considered, and the effects of wind on them are examined. The aim behind this work is to give designers rules and intuition on how air moves within a building; the research reveals a fascinating branch of fluid mechanics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.fluid.31.1.201
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular mixing in Rayleigh–Taylor instability. Part I: Global mixing (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1269-1277 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper describes experiments on the mixing produced by Rayleigh–Taylor instability between two miscible fluids. A layer of brine is placed over a layer of fresh water in a gravitational field, and the ensuing flow is visualized by laser-induced fluorescence and measurements are made of the concentration fields as the flow develops. It is found that large-scale disturbances develop which produce intermingling of the fluids, but molecular mixing occurs as a result of small-scale instabilities which grow on the edges of the larger scale motions. When the system overturns stably stratified fluid is produced, and the mixing efficiency of the process is measured and found to be large compared with other forms of mixing. It is suggested that this increased efficiency is due to the fact that much of the mixing occurs when the system is unstably stratified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858055
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  • 3
    Electronic Resource
    Electronic Resource
    Electrical measurement of sediment layer thickness under suspension flows (1999)
    Springer
    Experiments in fluids 26 (1999), S. 470-474 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  This paper reports a new technique to measure the thickness of a layer of deposited sediment as a function of time, independent of the flow conditions or presence of suspended sediment above the layer. Small electrodes on the bottom and a reference electrode in the fluid above were used to measure the resistance of the layer with a small AC current and a bridge circuit. Using a multiplexer and an Analog-to-Digital converter the growth of the layer can be accurately monitored at many locations on the tank bottom. In a trial experiment the sedimentation under a stagnant column of a monodisperse suspension was examined. The results show that changes in the sediment layer thickness of less than 0.3% can be measured for layers up to 0.2 g/cm2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480050311
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  • 4
    Electronic Resource
    Electronic Resource
    A bi-modal structure imposed on gravity driven boundary currents in rotating systems by effects of the bottom topography (1998)
    Springer
    Experiments in fluids 25 (1998), S. 388-391 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  An experimental observation related to the influence of the bottom topography on the development of gravity driven surface boundary currents in rotating systems is described and discussed. The results presented concern the local flow geometry in the vicinity of the head of the current. It is observed that, depending on the values of the independent experimental variables and the inclination angle of the bottom topography, the current propagates along the boundary with its head being either attached to or detached from the coastline. An appropriate scaling of the experimental data reveals that the attached and detached head mode occur in two distinct parameter regimes which are separated from each other by a well defined border. The discussion of the results suggests that this border identifies the division between two flow regimes in which the local flow structure in the vicinity of the head of the gravity current is and where it is not significantly influenced by the bottom topography.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480050245
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  • 5
    Electronic Resource
    Electronic Resource
    Intermittent baroclinic instability and fluctuations in geophysical circulations (1985)
    [s.l.] : Nature Publishing Group
    Nature 316 (1985), S. 801-803 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The condition of solid-body rotation (or zero motion relative to a rotating reference frame) can never be attained by a fluid containing gradients of temperature or chemical composition1. This is because diffusion of density across the curved surfaces of constant density drives a meridional ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/316801a0
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  • 6
    Electronic Resource
    Electronic Resource
    Microbursts: a hazard for aircraft (1985)
    [s.l.] : Nature Publishing Group
    Nature 317 (1985), S. 601-602 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The crash of the TriStar on 2 August 1985 as it came in to land at D^llas-Ft Worth has been attributed to a small but intense thunderstorm outflow, called a microburst. Microbursts are produced by localized downdrafts of cold air which originate at high altitudes. The downdrafts are typically a few ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/317601a0
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  • 7
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    Stability of a buoyancy-driven coastal current at the shelf break (2005)
    Cambridge University Press
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Cambridge University Press, 2002. This article is posted here by permission of Cambridge University Press for personal use, not for redistribution. The definitive version was published in Journal of Fluid Mechanics 452 (2002): 97-121, doi:10.1017/S0022112001006668.
    Description: Buoyancy-driven surface currents were generated in the laboratory by releasing buoyant fluid from a source adjacent to a vertical boundary in a rotating container. Different bottom topographies that simulate both a continental slope and a continental ridge were introduced in the container. The topography modified the flow in comparison with the at bottom case where the current grew in width and depth until it became unstable once to non-axisymmetric disturbances. However, when topography was introduced a second instability of the buoyancy-driven current was observed. The most important parameter describing the flow is the ratio of continental shelf width W to the width L* of the current at the onset of the instability. The values of L* for the first instability, and L*[minus sign]W for the second instability were not influenced by the topography and were 2–6 times the Rossby radius. Thus, the parameter describing the flow can be expressed as the ratio of the width of the continental shelf to the Rossby radius. When this ratio is larger than 2–6 the second instability was observed on the current front. A continental ridge allowed the disturbance to grow to larger amplitude with formation of eddies and fronts, while a gentle continental slope reduced the growth rate and amplitude of the most unstable mode, when compared to the continental ridge topography. When present, eddies did not separate from the main current, and remained near the shelf break. On the other hand, for the largest values of the Rossby radius the first instability was suppressed and the flow was observed to remain stable. A small but significant variation was found in the wavelength of the first instability, which was smaller for a current over topography than over a flat bottom.
    Description: Partial support for C.C. was provided by a TMR fellowship, MAS3-CT96-5017.
    Keywords: Buoyancy-driven currents ; Bottom topography
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: 750211 bytes
    Format: application/pdf
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  • 8
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    Characteristics of colliding sea breeze gravity current fronts : a laboratory study (2017)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Quarterly Journal of the Royal Meteorological Society 143 (2017): 1434–1441, doi:10.1002/qj.3015.
    Description: Sea and land breeze circulations driven by surface temperature differences between land and sea often evolve into gravity currents with sharp fronts. Along narrow peninsulas, islands and enclosed seas, sea/land breeze fronts from opposing shorelines may converge and collide and may initiate deep convection and heavy precipitation. Here we investigate the collision of two sea breeze gravity current fronts in an analogue laboratory setting. We examine these collisions by means of ‘lock-exchange’ experiments in a rectangular channel. The effects of differences in gravity current density and height are studied. Upon collision, a sharp front separating the two currents develops. For symmetric collisions (the same current densities and heights) this front is vertical and stationary. For asymmetric collisions (density differences, similar heights) the front is tilted, changes shape in time and propagates in the same direction as the heavier current before the collision. Both symmetric and asymmetric collisions lead to upward displacement of fluid from the gravity currents and mixing along the plane of contact. The amount of mixing along the collision front decreases with asymmetry. Height differences impact post-collision horizontal propagation: there is significant propagation in the same direction as the higher current before collision, independent of density differences. Collisions of two gravity current fronts force sustained ascending motions which increase the potential for deep convection. From our experiments we conclude that this potential is larger in stationary collision fronts from symmetric sea breeze collisions than in propagating collision fronts from asymmetric sea breeze collisions.
    Description: National Science Foundation Grant Number: OCE-0824636; Office of Naval Research Grant Number: N00014-09-1-0844; National Aeronautics and Space Administration Grant Number: NASA NNX14A078G
    Keywords: Sea breeze ; Land breeze ; Gravity current ; Convergence ; Deep convection ; GFD ; Fluid dynamics
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 9
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    Entrainment in two coalescing axisymmetric turbulent plumes (2014)
    Cambridge University Press
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © Cambridge University Press, 2014. This article is posted here by permission of Cambridge University Press for personal use, not for redistribution. The definitive version was published in Journal of Fluid Mechanics 752 (2014): R2, doi:10.1017/jfm.2014.389.
    Description: A model of the total volume flux and entrainment occurring in two coalescing axisymmetric turbulent plumes is developed and compared with laboratory experiments. The dynamical evolution of the two plumes is divided into three regions. In region 1, where the plumes are separate, the entrainment in each plume is unaffected by the other plume, although the two plumes are drawn together due to the entrainment of ambient fluid between them. In region 2 the two plumes touch each other but are not yet merged. In this region the total entrainment is a function of both the dynamics of the touching plumes and the reduced surface area through which entrainment occurs. In region 3 the two plumes are merged and the entrainment is equivalent to that in a single plume. We find that the total volume flux after the two plumes touch and before they merge increases linearly with distance from the sources, and can be expressed as a function of the known total volume fluxes at the touching and merging heights. Finally, we define an ‘effective’ entrainment constant, αeff, as the value of α needed to obtain the same total volume flux in two independent plumes as that occurring in two coalescing plumes. The definition of αeff allows us to find a single expression for the development of the total volume flux in the three different dynamical regions. This single expression will simplify the representation of coalescing plumes in more complex models, such as in large-scale geophysical convection, in which plume dynamics are not resolved. Experiments show that the model provides an accurate measure of the total volume flux in the two coalescing plumes as they evolve through the three regions.
    Description: The authors gratefully acknowledge the National Science Foundation (grant OCE-0824636) and the Office of Naval Research (grant N00014-09-1-0844) for their support of the 2013 WHOI Geophysical Fluid Dynamics Summer School where this project was initiated. Support to C.C. was given by the National Science Foundation project OCE-1130008.
    Description: 2015-07-11
    Keywords: Mixing ; Plumes/thermals ; Turbulent mixing
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 10
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    Symmetric coalescence of two hydraulic fractures (2018)
    National Academy of Sciences
    Details
    Publication Date: 2018-09-25
    Description: The formation of a fracture network is a key process for many geophysical and industrial practices from energy resource recovery to induced seismic management. We focus on the initial stage of a fracture network formation using experiments on the symmetric coalescence of two equal coplanar, fluid-driven, penny-shaped fractures in a brittle elastic medium. Initially, the fractures propagate independently of each other. The fractures then begin to interact and coalesce, forming a bridge between them. Within an intermediate period after the initial contact, most of the fracture growth is localized along this bridge, perpendicular to the line connecting the injection sources. Using light attenuation and particle image velocimetry to measure both the fracture aperture and velocity field, we characterize the growth of this bridge. We model this behavior using a geometric volume conservation argument dependent on the symmetry of the interaction, with a 2D approximation for the bridge. We also verify experimentally the scaling for the bridge growth and the shape of the thickness profile along the bridge. The influence of elasticity and toughness of the solid, injection rate of the fluid, and initial location of the fractures are captured by our scaling.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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