Littérature scientifique sur le sujet « Buoyancy fluxe »
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Articles de revues sur le sujet "Buoyancy fluxe"
1
KAY, ANTHONY. « Warm discharges in cold fresh water. Part 1. Line plumes in a uniform ambient ». Journal of Fluid Mechanics 574 (15 février 2007) : 239–71. http://dx.doi.org/10.1017/s0022112006004101.
Texte intégralRésumé :
Turbulent buoyant plumes in cold fresh water are analysed, assuming a quadratic dependence of density on temperature. The model is based on the assumption that entrainment velocity is proportional to vertical velocity in the plume. Numerical and asymptotic solutions are obtained for both rising and descending plumes from virtual sources with all possible combinations of buoyancy, volume and momentum fluxes. Physical sources can be identified as points on trajectories of plumes from virtual sources.The zero-buoyancy condition, at which the plume and the ambient have equal densities but their temperatures are on opposite sides of the temperature of maximum density, is of particular importance. If an upwardly buoyant plume rising through a body of water reaches the surface before passing through its zero-buoyancy level, it will form a surface gravity current; otherwise, the plume water will return to the source as a fountain. The height at which zero buoyancy is attained generally decreases as the source momentum flux increases: greater plume velocity produces greater entrainment and hence more rapid temperature change. Descending plumes, if ejected downwards against upward buoyancy, may be classified as strongly or weakly forced according to whether they reach the zero-buoyancy condition before being brought to rest. If they do, they continue to descend with favourable buoyancy; otherwise, they may form an inverted fountain. Once a descending plume has attained downward buoyancy, it can continue to descend indefinitely, ultimately behaving like a plume in a fluid with a linear equation of state. In contrast, a rising plume will eventually come to rest, however large its initial upward buoyancy and momentum fluxes are.
2
WELLS, M. G., R. W. GRIFFITHS et J. S. TURNER. « Competition between distributed and localized buoyancy fluxes in a confined volume ». Journal of Fluid Mechanics 391 (25 juillet 1999) : 319–36. http://dx.doi.org/10.1017/s0022112099005248.
Texte intégralRésumé :
We investigate the convection and density stratification that form when buoyancy fluxes are simultaneously applied to a finite volume in both a turbulent buoyant plume from a small source and as a uniform heat flux from a horizontal boundary. The turbulent plume tends to produce a stable density stratification, whereas the distributed flux from a boundary tends to force vigorous overturning and vertical mixing. Experiments show that steady, partially mixed and partially stratified states can exist when the plume buoyancy flux is greater than the distributed flux.When the two fluxes originate from the same boundary, the steady state involves a balance between the rate at which the mixed layer deepens due to encroachment and vertical advection of the stratified water far from the plume due to the plume volume flux acquired by entrainment. There is a monotonic relationship between the normalized mixed layer depth and flux ratio R (boundary flux/plume flux) for 0<R<1, and the whole tank overturns for R>1. The stable density gradient in the stratified region is primarily due to the buoyancy from the plume but is strengthened by a stabilizing temperature gradient resulting from entrainment of heat into the plume from the mixed layer. This result may be relevant to the upper oceans of high latitude where there is commonly a destabilizing heat flux from the sea surface as well as more localized and intense deep convection from the surface.For the case of fluxes from a plume on one boundary and a uniform heat flux from the opposite boundary the shape of the density profile is that given by the Baines & Turner (1969) ‘filling-box’ mechanism, with the gradient reduced by a factor (1 + R) due to the heating. Thus, when R<−1 there is no stratified region and the whole water column overturns. When 0>R>−1, the constant depth of the convecting layer is determined by a balance between buoyancy and turbulent kinetic energy in the outflow layer from the plume.
3
DIEZ, FRANCISCO J., et WERNER J. A. DAHM. « Effects of heat release on turbulent shear flows. Part 3. Buoyancy effects due to heat release in jets and plumes ». Journal of Fluid Mechanics 575 (mars 2007) : 221–55. http://dx.doi.org/10.1017/s0022112006004277.
Texte intégralRésumé :
An integral method is presented for determining effects of buoyancy due to heat release on the properties of reacting jets and plumes. This method avoids the Morton entrainment hypothesis entirely, and thus removes the ad hoc ‘entrainment modelling’ required in most other integral approaches. We develop the integral equation for the local centreline velocity uc(x), which allows modelling in terms of the local flow width δ (x). In both the momentum-dominated jet limit and buoyancy-dominated plume limit, dimensional arguments show δ (x) ≈ x, and experimental data show the proportionality factor cδ to remain constant between these limits. The entrainment modelling required in traditional integral methods is thus replaced by the observed constant cδ value in the present method. In non-reacting buoyant jets, this new integral approach provides an exact solution for uc(x) that shows excellent agreement with experimental data, and gives simple expressions for the virtual origins of jets, plumes and buoyant jets. In the exothermically reacting case, the constant cδ value gives an expression for the buoyancy flux B(x) that allows the integral equation for uc(x) to be solved for arbitrary exit conditions. The resulting uc(x) determines the local mass, momentum and buoyancy fluxes throughout the flow, as well as the centreline mixture fraction ζc(x) and thus the flame length L. The latter provides the proper parameters Ω andΛ that determine buoyancy effects on the flame, and provides power-law scalings in the momentum-dominated and buoyancy-dominated limits. Comparisons with buoyant flame data show excellent agreement over a wide range of conditions.
4
Cessi, Paola, et Christopher L. Wolfe. « Adiabatic Eastern Boundary Currents ». Journal of Physical Oceanography 43, no 6 (1 juin 2013) : 1127–49. http://dx.doi.org/10.1175/jpo-d-12-0211.1.
Texte intégralRésumé :
Abstract The dynamics of the eastern boundary current of a high-resolution, idealized model of oceanic circulation are analyzed and interpreted in terms of residual mean theory. In this framework, it is clear that the eastern boundary current is adiabatic and inviscid. Nevertheless, the time-averaged potential vorticity is not conserved along averaged streamlines because of the divergence of Eliassen–Palm fluxes, associated with buoyancy and momentum eddy fluxes. In particular, eddy fluxes of buoyancy completely cancel the mean downwelling or upwelling, so that there is no net diapycnal residual transport. The eddy momentum flux acts like a drag on the mean velocity, opposing the acceleration from the eddy buoyancy flux: in the potential vorticity budget this results in a balance between the divergences of eddy relative vorticity and buoyancy fluxes, which leads to a baroclinic eastern boundary current whose horizontal scale is the Rossby deformation radius and whose vertical extent depends on the eddy buoyancy transport, the Coriolis parameter, and the mean surface buoyancy distribution.
5
Hieronymus, Magnus, et Jonas Nycander. « The Buoyancy Budget with a Nonlinear Equation of State ». Journal of Physical Oceanography 43, no 1 (1 janvier 2013) : 176–86. http://dx.doi.org/10.1175/jpo-d-12-063.1.
Texte intégralRésumé :
Abstract The nonlinear equation of state of seawater introduces a sink or source of buoyancy when water parcels of unequal salinities and temperatures are mixed. This article contains quantitative estimates of these nonlinear effects on the buoyancy budget of the global ocean. It is shown that the interior buoyancy sink can be determined from surface buoyancy fluxes. These surface buoyancy fluxes are calculated using two surface heat flux climatologies, one based on in situ measurements and the other on a reanalysis, in both cases using a nonlinear equation of state. It is also found that the buoyancy budget in the ocean general circulation model Nucleus for European Modeling of the Ocean (NEMO) is in good agreement with the buoyancy budgets based on the heat flux climatologies. Moreover, an examination of the vertically resolved buoyancy budget in NEMO shows that in large parts of the ocean the nonlinear buoyancy sink gives the largest contribution to this budget.
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Nuijens, Louise, et Bjorn Stevens. « The Influence of Wind Speed on Shallow Marine Cumulus Convection ». Journal of the Atmospheric Sciences 69, no 1 (1 janvier 2012) : 168–84. http://dx.doi.org/10.1175/jas-d-11-02.1.
Texte intégralRésumé :
Abstract The role of wind speed on shallow marine cumulus convection is explored using large-eddy simulations and concepts from bulk theory. Focusing on cases characteristic of the trades, the equilibrium trade wind layer is found to be deeper at stronger winds, with larger surface moisture fluxes and smaller surface heat fluxes. The opposing behavior of the surface fluxes is caused by more warm and dry air being mixed to the surface as the cloud layer deepens. This leads to little difference in equilibrium surface buoyancy fluxes and cloud-base mass fluxes. Shallow cumuli are deeper, but not more numerous or more energetic. The deepening response is necessary to resolve an inconsistency in the subcloud layer. This argument follows from bulk concepts and assumes that the lapse rate and flux divergence of moist-conserved variables do not change, based on simulation results. With that assumption, stronger winds and a fixed inversion height imply larger surface moisture and buoyancy fluxes (heat fluxes are small initially). The consequent moistening tends to decrease cloud-base height, which is inconsistent with a larger surface buoyancy flux that tends to increase cloud-base height, in order to maintain the buoyancy flux at cloud base at a fixed fraction of its surface value (entrainment closure). Deepening the cloud layer by increasing the inversion height resolves this inconsistency by allowing the surface buoyancy flux to remain constant without further moistening the subcloud layer. Because this explanation follows from simple bulk concepts, it is suggested that the internal dynamics (mixing) of clouds is only secondary to the deepening response.
7
Deremble, Bruno, et W. K. Dewar. « First-Order Scaling Law for Potential Vorticity Extraction due to Wind ». Journal of Physical Oceanography 42, no 8 (1 août 2012) : 1303–12. http://dx.doi.org/10.1175/jpo-d-11-0136.1.
Texte intégralRésumé :
Abstract Surface sources and sinks of potential vorticity (PV) have been examined recently in various publications. These are normally identified as the mechanical and buoyant PV fluxes with the former scaled according to wind stress and the latter from buoyancy flux. The authors here examine a PV source that is often overlooked: namely, the diabatically forced source due to wind-driven deepening. Based on an idealized model of the mixed layer, the rate of deepening of the mixed layer due to wind is translated into PV extraction. The authors propose the first-order scaling law as an estimate of the net PV flux due to diabatic wind effects in the absence of other buoyancy effects. This law is verified and calibrated in several numerical experiments. Then, the authors compare the magnitude of the PV extraction due to wind to the other factors responsible for PV input/output: namely, air–sea heat flux, freshwater flux, and Ekman wind-driven currents. Finally, to illustrate the impact of the mixing induced by wind, the authors conclude with a global air–sea PV budget in the North Atlantic basin. The wind-driven diabatic PV flux is found to be comparable to all other sources in all cases and is distinguished by acting only to extract PV.
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Mirajkar, Harish N., Partho Mukherjee et Sridhar Balasubramanian. « On the dynamics of buoyant jets in a linearly stratified ambient ». Physics of Fluids 35, no 1 (janvier 2023) : 016609. http://dx.doi.org/10.1063/5.0136231.
Texte intégralRésumé :
We report mean flow and turbulence characteristics of a buoyant jet evolving in a linearly stratified ambient with stratification strength [Formula: see text]. The velocity and density fields are captured experimentally using simultaneous particle image velocimetry and planar laser-induced fluorescence technique. We report our findings by strategically choosing four axial locations such that it covers different flow regimes; namely, momentum-dominated region, buoyancy-dominated region, neutral buoyant layer, and plume cap region. The results at these axial locations are presented as a function of the radial co-ordinate to provide a whole field picture of the flow dynamics. From the mean axial velocity and density fields, it is seen that the velocity and the scalar (density) widths are of the same magnitude in the momentum-dominated region but show significant difference in the buoyancy-dominated region and beyond. It is also seen that the axial velocity for the buoyant jet is consistently higher than pure jet at different axial locations due to buoyancy-aided momentum. With the help of turbulent kinetic energy (TKE) budget analysis, it is seen that the shear production ( P) and TKE dissipation ([Formula: see text]) for a buoyant jet are higher compared to the case of pure jet at different axial locations, cementing the role of buoyancy and stratification on the flow dynamics. Further, it is observed that the buoyancy flux ( B) aids and destroys TKE intermittently in the radial direction, and it is at least [Formula: see text] smaller than P, [Formula: see text], and the mean flow buoyancy flux ( F). Finally, the relative strength of the turbulent transport of momentum to that of scalar in the radial direction is quantified using the turbulent Prandtl number, [Formula: see text]. It is seen that [Formula: see text] [Formula: see text] upto the neutral buoyant layer and [Formula: see text] 0.6 in the plume cap region. The current set of results obtained from experiments are first of its kind and elucidates various aspects of the flow which hitherto remained unknown and will also prove to be useful in testing numerical simulations for buoyancy-driven flows.
9
Kunze, Eric, John B. Mickett et James B. Girton. « Destratification and Restratification of the Spring Surface Boundary Layer in a Subtropical Front ». Journal of Physical Oceanography 51, no 9 (septembre 2021) : 2861–82. http://dx.doi.org/10.1175/jpo-d-21-0003.1.
Texte intégralRésumé :
AbstractDestratification and restratification of a ~50-m-thick surface boundary layer in the North Pacific Subtropical Front are examined during 24–31 March 2017 in the wake of a storm using a ~5-km array of 23 chi-augmented EM-APEX profiling floats (u, υ, T, S, χT), as well as towyo and ADCP ship surveys, shipboard air-sea surface fluxes, and parameterized shortwave penetrative radiation. During the first four days, nocturnal destabilizing buoyancy fluxes mixed the surface layer over almost its full depth every night followed by restratification to N ~ 2 × 10−3 rad s−1 during daylight. Starting on 28 March, nocturnal destabilizing buoyancy fluxes weakened because weakening winds reduced latent heat flux. Shallow mixing and stratified transition layers formed above ~20-m depth. A remnant layer in the lower part of the surface layer was insulated from destabilizing surface forcing. Penetrative radiation, turbulent buoyancy fluxes, and horizontal buoyancy advection all contribute to its restratification, closing the budget to within measurement uncertainties. Buoyancy advective restratification (slumping) plays a minor role. Before 28 March, measured advective restratification is confined to daytime; is often destratifying; and is much stronger than predictions of geostrophic adjustment, mixed-layer eddy instability, and Ekman buoyancy flux because of storm-forced inertial shear. Starting on 28 March, while small, the subinertial envelope of measured buoyancy advective restratification in the remnant layer proceeds as predicted by mixed-layer eddy parameterizations.
10
Hogg, Andrew J., Edward J. Goldsmith et Mark J. Woodhouse. « Unsteady turbulent line plumes ». Journal of Fluid Mechanics 856 (28 septembre 2018) : 103–34. http://dx.doi.org/10.1017/jfm.2018.698.
Texte intégralRésumé :
The unsteady ascent of a buoyant, turbulent line plume through a quiescent, uniform environment is modelled in terms of the width-averaged vertical velocity and density deficit. It is demonstrated that for a well-posed, linearly stable model, account must be made for the horizontal variation of the velocity and the density deficit; in particular the variance of the velocity field and the covariance of the density deficit and velocity fields, represented through shape factors, must exceed threshold values, and that models based upon ‘top-hat’ distributions in which the dependent fields are piecewise constant are ill-posed. Numerical solutions of the nonlinear governing equations are computed to reveal that the transient response of the system to an instantaneous change in buoyancy flux at the source may be captured through new similarity solutions, the form of which depend upon both the ratio of the old to new buoyancy fluxes and the shape factors.
Thèses sur le sujet "Buoyancy fluxe"
1
Ring, Michael J. 1979. « The role of eddies in buoyancy flux ». Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/114316.
Texte intégralRésumé :
Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2001.Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2001.
Cataloged from PDF version of thesis.
Includes bibliographical references (page 35).
This thesis explores the role of eddies in determining the stratification of the ocean through a laboratory experiment. The experiment uses a dual-tank apparatus, with a smaller tank sitting inside the larger tank. Both tanks sit on a rotating turntable, which simulates the rotation of Earth. During the experiment, salty water is pumped from the outer tank through small holes in the base of the inner tank, which is initially filled with fresh water. The evolution of the dense fluid in the inner tank is observed, with particular regard to the number of eddies that form. These observations are checked against theoretical predictions, derived from analysis of buoyancy flux, for the number of eddies expected to form.
by Michael J. Ring.
S.B.
2
Kulchoakrungsun, Ekapob. « Global simulations of heat-flux-driven buoyancy and magnetothermal instabilities, and their astrophysical implications ». Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/105598.
Texte intégralRésumé :
Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (page 36).
In this thesis, we investigate the convective instabilities induced by anisotropic conduction in a rapidly conducting plasma. We simulate the magneto-thermal instability (MTI), and the heat-flux-driven buoyancy instability (HBI) in two- and three- dimensional, global hydrodynamic simulations performed by the AREPO code, and verify the results of previous works. Our results have important astrophysical implications, such as the conductive heat transport in galaxy clusters.
by Ekapob Kulchoakrungsun.
S.B.
3
Nozawa, Satoshi. « Three-dimensional magnetohydrodynamic simulation of nonlinear magnetic buoyancy instability of flux sheets with magnetic shear ». 京都大学 (Kyoto University), 2006. http://hdl.handle.net/2433/144351.
Texte intégralRésumé :
Kyoto University (京都大学)0048
新制・論文博士
博士(理学)
乙第11770号
論理博第1464号
新制||理||1442(附属図書館)
23825
UT51-2006-C692
名古屋大学大学院理学研究科宇宙理学第２類
(主査)教授 柴田 一成, 教授 長田 哲也, 助教授 戸谷 友則
学位規則第4条第2項該当
4
Reid, W. J. « Experimental investigation of circumferentially non-uniform heat flux on the heat transfer coefficient in a smooth horizontal tube with buoyancy driven secondary flow ». Diss., University of Pretoria, 2005. http://hdl.handle.net/2263/66236.
Texte intégralRésumé :
Most heat transfer tubes are designed for either fully uniform wall temperature or fully uniform wall
heat flux boundary conditions under forced convection. Several applications, including but not limited
to the solar collectors of renewable energy systems, do however operate with non-uniform boundary
conditions. Limited research has been conducted on non-uniform wall heat flux heat transfer
coefficients in circular tubes, especially for mixed convection conditions. Such works are normally
numerical in nature and little experimental work is available. In this experimental investigation the
effects of the circumferential heat flux distribution and heat flux intensity on the single phase (liquid)
internal heat transfer coefficient were considered for a horizontal circular tube. Focus was placed on
the laminar flow regime of water within a stainless steel tube with an inner diameter of 27.8 mm and
a length to diameter ratio of 72. Different outer wall heat flux conditions, including fully uniform and
partially uniform heat fluxes were studied for Reynolds numbers ranging from 650 to 2 600 and a
Prandtl number range of 4 to 7. The heat flux conditions included 360˚ (uniform) heating, lower 180˚
heating, upper 180˚ heating, 180˚ left and right hemispherical heating, lower 90˚ heating, upper 90˚
heating and slanted 180˚ heating. Depending on the angle span of the heating, local heat fluxes of 6
631 W/m2
, 4 421 W/m2
, 3 316 W/m2
, 2 210 W/m2
and 1 658 W/m2 were applied. Results indicate that
the local and average steady state Nusselt numbers are greatly influenced by the applied heat flux
position and intensity. Highest average heat transfer coefficients were achieved for case where the
applied heat flux was positioned on the lower half (in terms of gravity) of the tubes circumference,
while the lowest heat transfer coefficients were achieved when the heating was applied to the upper
half of the tube. Variations in the heat transfer coefficient were found to be due to the secondary
buoyancy induced flow effect. The relative thermal performance of the different heating scenarios
where characterised and described by means of newly developed heat transfer coefficient
correlations for fully uniform heating, lower 180° heating, and upper 180° heating.Dissertation (MEng)--University of Pretoria, 2018.
Mechanical and Aeronautical Engineering
MEng
Unrestricted
5
Jameel, Syed Mohd Saad. « Turbulence modelling of mixed and natural convection regimes in the context of the underhood-space of automobiles ». Thesis, Pau, 2020. http://www.theses.fr/2020PAUU3033.
Texte intégralRésumé :
Le sujet de cette thèse concerne la modélisation de la turbulence des écoulements influencés par la flottabilité, qui émanent de l’interaction de la force gravitationnelle avec une différence de densité. Cette étude est motivée par des problématiques rencontrées par le groupe PSA dans la simulation des écoulements de convection naturelle dans le compartiment moteur des véhicules.L’objectif principal de ce travail est de tester plusieurs modéles pour prendre en compte la flottabilité et de proposer des améliorations efficaces qui pourraient fournir un modèle applicable aux écoulements engendrés par la flottabilité. En outre, ces modifications doivent pouvoir être mises en œuvre dans le code Ansys Fluent pour le calcul des écoulements de convection naturelle dans les problèmes typiques cités ci-dessus. Dans le cadre de cet objectif, nous avons adapté trois modèles à viscosité turbulente aux effets de la flottabilité. La première approche qui offre le meilleur cadre physique implique l’extension des lois de comportement pour le tenseur de Reynolds et le flux thermique turbulent de manière linéaire, pour tenir compte de l’influence anisotrope de la flottabilité.Cette approche, appliquée à trois modèles différents, permet d’améliorer considérablement les résultats en reproduisant l’écoulement moyen et les quantités turbulentes. Dès lors, on se rend compte que cette approche conduit à des améliorations significatives en terme de physique.De plus, on observe que l’utilisation d’une approche simplifée d’hypothèse de diffusion par simple gradient “SGDH” pour modéliser le terme source de flottabilité conduit à une sous-estimation de l’effet de la flottabilité sur la turbulence. En outre, la comparaison avec les données de la simulation numérique directe (DNS) montre que l’hypothèse de diffusion par gradient généralisé “GGDH” donne de meilleures prédictions de l’écoulement moyen et du champ de température. Un autre aspect abordé dans ce travail concerne la sensibilité au modéle du terme de production par flottabilité dans l’equation de ε ou ω. Après une analyse détaillée, on constate que les résultats sont trés sensibles à ce terme et que la valeur optimale du coefficient est liée au choix du modèle de turbulence. Pour éviter cette sensibilité, on utilise une autre expression du terme source pour la modélisation de la flottabilité dans les équations de ε du ω qui tient compte du nombre de Richardson de flux et on observe une amélioration de la prédiction des profils moyens.Trois régimes différents d’écoulements sont étudiés, à savoir les régimes de convection forcée, mixte et naturelle. Parmi ceux-ci, la configuration de canal vertical différentiellement chauffé est considérée pour développer le modèle adapté à la flottabilité. C’est celle qui pose le plus grand défi pour les modèles à viscosité turbulente. Ces études ont abouti à la proposition d’une forme plus physique et simplifiée de modèles adaptés à la flottabilité, qui est considérée comme le meilleur compromis entre la précision physique et la stabilité numérique pour des écoulements induits par la flottabilité.Ces modèles sensiblisés à la flottabilité offrent des perspectives pour étudier d’autres configurations d’écoulements de convection mixte et naturelle et ouvrent la voie à l’utilisation de ces modèles dans les simulations dans le compartiment moteur des véhiculesThe subject of this thesis is the turbulence modeling of buoyancy-driven flows, which emanate through the interaction of the gravitational force with a density difference. The motivation of this investigation comes from the problem faced by the PSA group in simulating natural convection flows in the under hood space of cars.The main goal of the present investigation is to test several models to account for buoyancy and to propose effective improvements which could provide a model applicable to buoyancy-driven flows and in addition to that, can be easily implemented in the software Ansys Fluent for the computation of natural convection flows in the Underhood-space of cars.In the context of this goal, three eddy-viscosity turbulence models are sensitized to the effects of buoyancy. The first approach which offers the better physical framework involves the extension of the constitutive relations for the Reynolds stress and turbulent heat flux in a linear way, to account for the anisotropic influence of buoyancy. This approach is applied to three different models and brings in drastic improvement of the results in reproducing the mean flow and the turbulent quantities and thus it is realized that this approach leads to physically based improvements.Furthermore, it is observed that, using a simple gradient diffusion hypothesis (SGDH) approach to model the buoyancy source terms leads to underestimate the effect of buoyancy on turbulence and the comparison with the DNS data shows that the generalized gradient diffusion hypothesis (GGDH) give improved predictions of the mean flow and temperature field. Another issue addressed in this work involves the sensitiveness to the buoyancy production term in the ε or ω equations and after a detailed analysis, it is realized that the results are very sensitive to this term and the optimal value of the coefficient is linked to the choice of the turbulence model. To avoid this limitation, another expression for the model of the buoyancy source term in the ε or ω equations is applied which considers the flux Richardson number and it is observed that there is an improvement in the prediction of mean flow profiles.Three different regimes of convective flows are studied namely, forced, mixed and natural convection and the more challenging differentially heated vertical channel flow configuration which poses a major challenge to the eddy-viscosity models is considered to develop the buoyancy sensitized model. As an outcome of these studies, the more physical and simplified forms of buoyancy sensitized model are proposed which is considered as the best compromise between the physical accuracy and numerical stability for buoyancy-driven flows.These buoyancy-sensitized models provide an opportunity to investigate other buoyancy-driven flows and paves the way for these models to be applied in the under hood space simulation
6
Omara, Abdeslam. « Étude de la convection mixte transitoire conjuguée dans une conduite verticale épaisse ». Besançon, 2008. http://www.theses.fr/2008BESA2050.
Texte intégralRésumé :
On présente les résultats d’une simulation numérique de la convection mixte conjuguée transitoire dans un tube vertical soumis à un flux DED chaleur constant et uniforme. Le fluide pénètre au haut du tube pour se diriger vers le bas ; par conséquent on est en présence d’un écoulement de convection mixte contrariée. Les équations de conservation dans le fluide et dans la paroi sont résolues numériquement en utilisant la méthode des volumes finis. Le couplage pression-vitesse est assuré en utilisant l’algorithme simple. On étudie l’influence des propriétés physiques et géométriques sur l’évolution transitoire des grandeurs thermiques (flux de chaleur à l’interface paroi-fluide et distribution radiale de température) et sur les grandeurs dynamiques (coefficient de frottement et champs vecteurs vitesses)The proposed survey in this thesis appears in the setting of the conjugated laminar and transient mixed convection in a thick vertical conduct submitted to a constant and uniform heat flux. The fluid penetrates to the top of the conduct to head downwards, therefore one is in presence of opposed mixed convection flow. The governing transport equations were solved using the finite volume formulation and the simple algorithm is adopted. We study the effect of physical and geometrical properties of the physical system on the transient evolution of the thermal magnitudes (interfacial heat flux and radial distribution of the temperature) and the hydrodynamic magnitudes (friction coefficient and vector velocities)
7
Wong, William Chiu-Kit. « CFD Flame Spread Model Validation : Multi-Component Data Set Framework ». Digital WPI, 2012. https://digitalcommons.wpi.edu/etd-theses/918.
Texte intégralRésumé :
"Review of the literature shows that the reported correlation between predictions and experimental data of flame spread vary greatly. The discrepancies displayed by the models are generally attributed to inaccurate input parameters, user effects, and inadequacy of the model. In most experiments, the metric to which the model is deemed accurate is based on the prediction of the heat release rate, but flame spread is a highly complex phenomenon that should not be simplified as such. Moreover, fire growth models are usually made up of distinctive groups of calculation on separate physical phenomena to predict processes that drive fire growth. Inaccuracies of any of these “sub-models” will impact the overall flame spread prediction, hence identifying the sources of error and sensitivity of the subroutines may aid in the development of more accurate models. Combating this issue required that the phenomenon of flame spread be decomposed into four components to be studied separately: turbulent fluid dynamics, flame temperature, flame heat transfer, and condensed phase pyrolysis. Under this framework, aspects of a CFD model may be validated individually and cohesively. However, a lack of comprehensive datasets in the literature hampered this process. Hence, three progressively more complex sets of experiments, from free plume fires to fires against an inert wall to combustible wall fires, were conducted in order to obtain a variety of measurements related to the four inter-related components of flame spread. Multiple permutations of the tests using different source fuels, burner size, and source fire heat release rate allowed a large amount of comparable data to be collected for validation of different fire configurations. FDS simulations using mostly default parameters were executed and compared against the experimental data, but found to be inaccurate. Parametric study of the FDS software shows that there are little definitive trends in the correlation between changes in the predicted quantities and the modeling parameters. This highlights the intricate relationships shared between the subroutines utilized by FDS for calculations related to the four components of flame spread. This reveals a need to examine the underlying calculation methods and source code utilized in FDS."
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Snow, Kate. « Antarctic Bottom Water response to Varying Surface Fluxes ». Phd thesis, 2016. http://hdl.handle.net/1885/110705.
Texte intégralRésumé :
Antarctic Bottom Water (AABW) is one of the densest and most
voluminous water masses of the global ocean. It forms the lower
limb of the global overturning circulation and plays an important
role in transporting carbon, heat and freshwater sequestered from
the atmosphere to the deep ocean. Surface buoyancy fluxes
modulate the production of AABW through the formation of Dense
Shelf Water (DSW) on the Antarctic continental shelf. The DSW
flows down the continental slope as an overflow, entraining
ambient Circumpolar Deep Water (CDW), to form AABW. The AABW
spreads through the abyssal ocean, influencing global deep
stratification, water properties and circulation over centennial,
and even millennial, time scales
While surface fluxes play a key role in defining AABW production
rates, the role of varying surface fluxes in influencing AABW
properties and variability remains uncertain. Broad scale
observational analysis of AABW processes is hindered by the
extreme conditions particular to the Southern Ocean and Antarctic
regions, and climate models struggle to accurately represent AABW
formation processes. The difficulty climate models have in
representing AABW formation originates from challenges in
simulating DSW formation and the resultant overflow. Through both
observational analysis and novel model development, this thesis
provides insight into the role of varying surface fluxes in
controlling AABW responses and feedbacks, and the limitations of
climate models in representing such responses.
A coarse resolution sector model of the Atlantic Ocean is
developed to aid in testing the limitations of climate model
representation of AABW formation. With realistic forcing and
bathymetry, the sector model efficiently emulates climate model
processes and allows AABW sensitivity to overflow
parameterisations to be assessed. While AABW proves relatively
insensitive to most current generation overflow
parameterisations, understanding the importance of DSW formation
in defining AABW's role in a changing climate remains an
important challenge.
Increased horizontal and vertical resolution allows the sector
model to maintain DSW as the dominate mode of AABW formation.
Under such formation conditions, the influence of varying surface
buoyancy fluxes on DSW sourced AABW is assessed. Increased
buoyancy fluxes decrease the cross-shelf exchange of DSW and CDW.
The reduced exchange cools DSW and propagates changes to the
abyssal ocean, driving a decadal scale variability of AABW.
The role of surface buoyancy variations in driving the
cross-shelf exchange and AABW production, is further revealed at
seasonal time scales through an observational analysis of
circulation on the Adelie Land continental shelf, East
Antarctica. The seasonality of surface buoyancy fluxes leads to
enhanced cross-shelf exchange of DSW and CDW in winter, at an
order of magnitude larger than that in summer. The enhanced
exchange sets up a cyclonic flow on the shelf and highlights the
influence of buoyancy fluxes in controlling circulation on the
continental shelf.
The influence of surface buoyancy fluxes on AABW formation, shelf
circulation and cross-shelf exchange, occurs through inclusion of
DSW sourced AABW, a process absent from most climate models.
Without correct representation of AABW formation mechanisms,
climate models are missing key responses and feedbacks driven
from changes in surface fluxes. On-going work into climate model
development of AABW formation processes is thus essential to
develop an increased understanding of AABW dynamics, variability
and response to climate change.
Livres sur le sujet "Buoyancy fluxe"
1
Kraus, Eric B., et Joost A. Businger. Atmosphere-Ocean Interaction. Oxford University Press, 1995. http://dx.doi.org/10.1093/oso/9780195066180.001.0001.
Texte intégralRésumé :
With both the growing importance of integrating studies of air-sea interaction and the interest in the general problem of global warming, the appearance of the second edition of this popular text is especially welcome. Thoroughly updated and revised, the authors have retained the accessible, comprehensive expository style that distinguished the earlier edition. Topics include the state of matter near the interface, radiation, surface wind waves, turbulent transfer near the interface, the planetary boundary layer, atmospherically-forced perturbations in the oceans, and large-scale forcing by sea surface buoyancy fluxes. This book will be welcomed by students and professionals in meteorology, physical oceanography, physics and ocean engineering.
Chapitres de livres sur le sujet "Buoyancy fluxe"
1
Ivey, G. N., J. Imberger et J. R. Koseff. « Buoyancy fluxes in a stratified fluid ». Dans Physical Processes in Lakes and Oceans, 377–88. Washington, D. C. : American Geophysical Union, 1998. http://dx.doi.org/10.1029/ce054p0377.
Texte intégral
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Bacon, Sheldon, Paul G. Myers, Bert Rudels et David A. Sutherland. « Accessing the Inaccessible : Buoyancy-Driven Coastal Currents on the Shelves of Greenland and Eastern Canada ». Dans Arctic–Subarctic Ocean Fluxes, 703–22. Dordrecht : Springer Netherlands, 2008. http://dx.doi.org/10.1007/978-1-4020-6774-7_29.
Texte intégral
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Sidi, C., et F. Dalaudier. « Temperature and Heat Flux Spectra in the Turbulent Buoyancy Subrange ». Dans Middle Atmosphere, 547–69. Basel : Birkhäuser Basel, 1989. http://dx.doi.org/10.1007/978-3-0348-5825-0_24.
Texte intégral
4
Macintyre, Sally, Werner Eugster et George W. Kling. « The Critical Importance of Buoyancy Flux for Gas Flux Across the Air-Water Interface ». Dans Gas Transfer at Water Surfaces, 135–39. Washington, D. C. : American Geophysical Union, 2013. http://dx.doi.org/10.1029/gm127p0135.
Texte intégral
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Kuznetsov, V. D. « Magnetic Buoyancy with Viscosity and Ohmic Dissipation and Flux Tube Formation ». Dans Basic Plasma Processes on the Sun, 58–59. Dordrecht : Springer Netherlands, 1990. http://dx.doi.org/10.1007/978-94-009-0667-9_11.
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Korotaev, G. K. « Circulation in Semi-Enclosed Seas Induced by Buoyancy Flux through a Strait ». Dans Sensitivity to Change : Black Sea, Baltic Sea and North Sea, 395–401. Dordrecht : Springer Netherlands, 1997. http://dx.doi.org/10.1007/978-94-011-5758-2_30.
Texte intégral
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Kraus, Eric B., et Joost A. Businger. « Large-Scale Forcing by Sea Surface Buoyancy Fluxes ». Dans Atmosphere-Ocean Interaction. Oxford University Press, 1995. http://dx.doi.org/10.1093/oso/9780195066180.003.0012.
Texte intégralRésumé :
This chapter deals with convective fluxes of sensible heat, moisture, and salinity that originate at the sea surface. In Section 8.1 we consider the relative influence of oceanic and atmospheric variability upon these fluxes. The general character of deep convection and its occurrence in the polar oceans is discussed in Section 8.2. The case of deep convection over the ocean in the tropical atmosphere, which is somewhat more complicated because of compressibility and cloud formation, is discussed in Section 8.3. Finally, in Section 8.4, we consider some of the long-term ocean-atmosphere feedback processes. Kinetic energy in the atmosphere-ocean system is derived mainly from an upward flux of buoyancy. The resulting redistribution of mass reduces available potential energy APE and lowers the centre of gravity. In turn, APE is generated, primarily by non-adiabatic processes: unequal absorption and emission of radiation; local release of latent heat in the atmosphere; local salinity changes in the ocean; and unequal heat conduction from the boundaries. The total mass of the oceans is about 280 times that of the atmosphere; their heat capacity is nearly 1200 times larger. Oceanic response times to external forcing are correspondingly slower. Although the annual irradiation cycle affects only a small part of the water mass, the thermal inertia is strong enough to prevent large or fast temperature variations. It is well known that this has a dominant influence on the whole terrestrial climate. This influence is particularly strong in the marine temperate regions. Figure 5.10 showed that even the daily temperature changes of the surface waters are smaller than those in the air. By virtue of their mechanical and thermal inertia, the oceans tend to play the role of a flywheel in the air-sea system. The atmosphere is the more volatile and more variable partner. It supplies mechanical energy to the oceans at a rate that has a very skewed distribution in space and time because the work of the wind stress is proportional to the third power of the windspeed. This creates a strong bias in favour of restricted stormy areas.
8
Zhang, Jiawei, Marwan Katurji, Peyman Zawar-Reza et cTara Strand. « The role of helicity and fire-atmosphere turbulent energy transfer on potential wildfire behavior ». Dans Advances in Forest Fire Research 2022, 1539–49. Imprensa da Universidade de Coimbra, 2022. http://dx.doi.org/10.14195/978-989-26-2298-9_235.
Texte intégralRésumé :
Understanding near surface fire-atmosphere interactions at turbulence scale is fundamental for predicting fire spread behavior. This study investigated the fire-atmosphere interaction and the accompanying energy transport processes within the convective boundary layer. Three groups of large eddy simulations (LES) representing common ranges of convective boundary layer conditions (resulting from land surface heat flux ranging from 120 to 360W/m2) and fire intensities (50 to 150kW/m2) were used to examine how ambient buoyancy-induced atmospheric turbulence can impact fire region heat and momentum transport. In a relatively weak convective boundary layer, the change of near-surface atmospheric turbulence caused by the buoyancy force from the fire heat release is substantial and can cause an anticorrelation of the helicity between the ambient atmosphere and the fire-induced flow. Fire-induced impact becomes much smaller in a relatively strong convective environment with ambient atmospheric flow maintaining coherent structures including vortices across the fire heating region. The helicity also shows strong correlation between the ambient atmosphere and the fire-induced flow. A further energy transport efficiency analysis shows a narrow heat transport zone above the fire line for the weak convective boundary layer scenario. This indicates confined heat release and stronger fire-induced buoyancy force. The high-efficiency heat transport zone becomes much wider in a stronger convective boundary layer which leads to a wider distribution of heat released from fire, the weaker fire-induced buoyancy force and causes less fire-induced flow-field change. The work also found counter-gradient transport zones of both momentum and heat in fire cases in the weak convective boundary layer group. The counter-gradient transport might indicate the existence of strong buoyancy-induced mixing processes.
9
Verma, Mahendra K., Abhishek Kumar et Anando G. Chatterjee. « Energy Spectrum and Flux of Buoyancy-Driven Turbulence ». Dans Advances in Computation, Modeling and Control of Transitional and Turbulent Flows, 442–51. WORLD SCIENTIFIC, 2015. http://dx.doi.org/10.1142/9789814635165_0044.
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Gong, Weixuan, Juan Cuevas et Albert Simeoni. « A Study of the Ignition Mechanism for Dead Pinus Palustris Needles ». Dans Advances in Forest Fire Research 2022, 498–504. Imprensa da Universidade de Coimbra, 2022. http://dx.doi.org/10.14195/978-989-26-2298-9_77.
Texte intégralRésumé :
Combinations of cumulative impacts of drought, invasive species, climate variability, and ever-expanding wildland-urban interface make landscapes more susceptible to devastating wildland fires. To treat the increasing risks of wildland fires, one of the ways is to mitigate the risk of ignition, which requires a solid understanding of the ignition mechanism of vegetation fuels. This can be achieved mainly through discerning the degradation stage and the ignition criteria. Scaling up the experiments for the degradation stage and evaluating the suitability of existing ignition criteria are two of the primary challenges for ignition studies on vegetation fuels. Motivated by the challenges, two series of experiments were conducted using a modified Cone Calorimeter to understand the mechanisms driving the ignition of dead Pinus palustris needles. In the first set of experiments, the ignition of pine needles was studied for varied incident heat fluxes (20-35 kW/m2) and air flow rates (buoyancy-induced - 100 l/min forced flow). In the second set of experiments, Fourier transform infrared (FTIR) spectroscopy was used to characterize the composition of the pyrolysis gases generated from the thermal degradation of pine needles when exposed to various incident heat fluxes (20-35 kW/m2) under an inert atmosphere obtained using a flow of pure nitrogen (50-100 l/min). The results for the first series of experiments show that critical mass loss rate at ignition increase with both flow rates and heat flux, while the heat release rate at ignition was only influenced by the flow conditions. From the second set of experiments, it was found that methane (CH4), carbon monoxide (CO), carbon dioxide (CO2), and water vapor (H2O) are the main constituents of the pyrolysis gases. The predominance of these compounds was found to be independent of the external heat flux while their individual concentrations are sensitive to it. The flammability of pyrolysis gas was found to increase with external heat flux. The average content of flammable species, CH4 and CO, in the pyrolysis gas account for more than 31% at 20 kW/m2 and more than 40% at 30 kW/m2.
Actes de conférences sur le sujet "Buoyancy fluxe"
1
Du, Zhongxuan, Wensheng Lin et Anzhong Gu. « Numerical Study on Supercritical CH4/N2 Cooling in a Horizontal Tube ». Dans ASME 2012 Heat Transfer Summer Conference collocated with the ASME 2012 Fluids Engineering Division Summer Meeting and the ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/ht2012-58259.
Texte intégralRésumé :
Coalbed methane (CBM) is a kind of mixed gas with the principal component of methane and nitrogen. Supercritical convective heat transfer of CH4/N2 cooled in horizontal circular tubes is one of the most important heat transfer processes during CBM liquefaction. In this paper, supercritical CH4/N2 cooling has been numerically investigated in a horizontal tube by using the low Reynolds number turbulence model proposed by Lam and Bremhorst. The study first focuses on the effect of nitrogen content on CBM heat transfer characteristics. The results indicate that supercritical convective heat transfer of CBM is mainly affected by the fact that the CBM properties change with nitrogen content. Then the study focuses on the buoyancy effect on heat transfer characteristics at different mass fluxes, heat fluxes and pressures. The results show that buoyancy effect increases with the decrease of mass flux or with the increase of heat flux, and the relationship Gr/Re2.7 predicts the buoyancy effect onset better than Gr/Re2. When the buoyancy effect is considerably strong, buoyancy effect on heat transfer in the top line of the horizontal circular tube is equivalent to buoyancy-opposed heat transfer, and buoyancy effect on heat transfer in the bottom line to buoyancy-aided heat transfer. The correlation of buoyancy-opposed heat transfer proposed by Bruch et al. predicts well for the supercritical heat transfer of methane. When the buoyancy effect is negligible, the calculated results agree well with the Gnielinski correlation.
2
Togia, Harrison F. R., Clinton P. Conrad, Paul Wessel et Garrett Ito. « NEW CONSTRAINTS ON TEMPORAL VARIATIONS IN HAWAIIAN PLUME BUOYANCY FLUX ». Dans 113th Annual GSA Cordilleran Section Meeting - 2017. Geological Society of America, 2017. http://dx.doi.org/10.1130/abs/2017cd-292624.
Texte intégral
3
Smith, Madison N., et Claudia Adam. « TEMPORAL EVOLUTION OF BUOYANCY AND VOLCANISM FLUXES ALONG THE LOUISVILLE HOTSPOT ». Dans GSA Annual Meeting in Phoenix, Arizona, USA - 2019. Geological Society of America, 2019. http://dx.doi.org/10.1130/abs/2019am-331191.
Texte intégral
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Xu, X. Y., T. Ma, M. Zeng et Q. W. Wang. « Numerical Study of the Effects of Different Buoyancy Models on Supercritical Flow and Heat Transfer ». Dans ASME 2013 Heat Transfer Summer Conference collocated with the ASME 2013 7th International Conference on Energy Sustainability and the ASME 2013 11th International Conference on Fuel Cell Science, Engineering and Technology. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/ht2013-17295.
Texte intégralRésumé :
Due to the dramatic changes in physical properties, the flow and heat transfer in supercritical fluid are significantly affected by buoyancy effects, especially when the ratio of inlet mass flux and wall heat flux is relatively small. In this study, the heat transfer of supercritical water in uniformly heated vertical tube is numerically investigated with different buoyancy models which are based on different calculation methods of the turbulent heat flux. The applicabilities of these buoyancy models are analyzed both in heat transfer enhancement and deterioration conditions. The simulation results show that these buoyancy models make few differences and give good wall temperature prediction in heat transfer enhancement condition when the ratio of inlet mass flux and wall heat flux is very small. With the increase of wall heat flux, the accuracy of wall temperature prediction reduces, and the differences between these buoyancy models become larger. No buoyancy model can currently make accurate wall temperature prediction in deterioration condition in this study.
5
So, R. M. C., L. H. Jin et T. B. Gatski. « An Explicit Algebraic Model for Turbulent Buoyant Flows ». Dans ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45347.
Texte intégralRésumé :
This paper presents a derivation of an explicit algebraic stress model (EASM) and an explicit algebraic heat flux model (EAHFM) for buoyant shear flows. The models are derived using a projection methodology. The derived EASM has a four-term representation and is applicable to 2-D and 3-D flows. It is an extension of the three-term EASM for incompressible flow and the fourth term is added to account for the effect of buoyancy. The projection methodology is further extended to treat the heat flux transport equation in the derivation of an EAHFM. Again, the weak equilibrium assumption is invoked for the scaled heat flux equation. The basis vector used to represent the scaled heat flux vector is formed with the mean temperature gradient vector and 3×3 tensors, not necessarily symmetric or traceless, deduced from the shear and rotation rate tensors and the stress anisotropy tensor. An explicit algebraic model for buoyant shear flows is then formed with the derived EASM and EAHFM. From the derived EAHFM, an expression for the thermal diffusivity tensor in buoyant shear flows can be deduced. Thus, a turbulent Prandtl number for each of the three heat flux directions can be determined. These Prandtl numbers are functions of the gradient Richardson number. Alternatively, a scalar turbulent Prandtl number can be derived; its value is compared with the directional turbulent Prandtl numbers. The EASM and EAHFM are specialized to calculate 2-D homogeneous buoyant shear flows and the results are compared with direct numerical simulation (DNS) data and other model predictions. Good agreement with DNS data and other model predictions is obtained.
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Pantzlaff, Lars, et Richard M. Lueptow. « Transient Character of Positively and Negatively Buoyant Turbulent Jets ». Dans ASME 1997 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/imece1997-1247.
Texte intégralRésumé :
Abstract The transient character of the jet issuing from an upward nozzle centered in the bottom of a vertical cylindrical tank into bulk liquid of a different density was measured for varying jet Reynolds numbers and ratios of fluid densities using flow visualization and PIV. Positively buoyant jets penetrate to the free surface, driven by both momentum and buoyancy in the upward direction. The lighter jet fluid stratifies in a layer above the bulk liquid. Upon starting, a negatively buoyant jet has three stages. First the jet penetrates to its maximum height in the tank. Then the jet penetration decreases due to the downward backflow of heavier fluid surrounding the jet, which reduces the jet’s upward momentum. Finally the jet penetration height fluctuates around a mean value about 70% the maximum height of penetration. For small negative densimetric Froude numbers (−6075 ≤ Fr ≤ −250), the flow is fountain-like. The downward flow turns radially outward as it reaches the bottom of the tank and eventually an annular recirculation zone forms at the bottom of the tank with vortical motion opposite the vorticity of the inflowing jet. For large negative Froude numbers (Fr ≤ −7770), the spreading of the jet extends far enough so the annular downward flow is along the walls of the tank resulting in a large annular recirculation zone. Scaling the jet penetration and time with the buoyancy flux and the jet momentum flux results in collapse of the transient jet penetration over a wide range of Froude numbers.
7
Randle, Lindsey V., et Brian M. Fronk. « Investigation of Buoyancy Effects in Asymmetrically Heated Near-Critical Flows of Carbon Dioxide in Horizontal Microchannels Using Infrared Thermography ». Dans ASME 2021 Heat Transfer Summer Conference collocated with the ASME 2021 15th International Conference on Energy Sustainability. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/ht2021-63004.
Texte intégralRésumé :
Abstract In this study, we use infrared thermography to calculate local heat transfer coefficients of top and bottom heated flows of near-critical carbon dioxide in an array of parallel microchannels. These data are used to evaluate the relative importance of buoyancy for different flow arrangements. A Joule heated thin wall made of Inconel 718 applies a uniform heat flux either above or below the horizontal flow. A Torlon PAI test section consists of three parallel microchannels with a hydraulic diameter of 923 μm. The reduced inlet temperature (TR = 1.006) and reduced pressure (PR = 1.03) are held constant. For each heater orientation, the mass flux (520 kgm−2s−2 ≤ G ≤ 800 kgm−2s−2) and heat flux (4.7 Wcm−2 ≤ q″ ≤ 11.1 Wcm−2) are varied. A 2D resistance network analysis method calculates the bulk temperatures and heat transfer coefficients. In this analysis, we divide the test section into approximately 250 segments along the stream-wise direction. We then calculate the bulk temperatures using the enthalpy from the upstream segment, the heat flux in a segment, and the pressure. To isolate the effect of buoyancy, we screen the data to omit conditions where flow acceleration may be important or where relaminarization may occur. In the developed region of the channel, there was a 10 to 15 percent reduction of the local heat transfer coefficients for the upward heating mode compared to downward heating with the same mass and heat fluxes. Thus buoyancy effects should be considered when developing correlations for these types of flow.
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Sakamoto, Hitoshi, et Francis A. Kulacki. « Buoyancy-Driven Flow in Saturated Porous Media ». Dans ASME 2005 Summer Heat Transfer Conference collocated with the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems. ASMEDC, 2005. http://dx.doi.org/10.1115/ht2005-72435.
Texte intégralRésumé :
Buoyancy-driven convection on a vertical, constant heat flux surface that bounds a fluid-saturated porous medium is experimentally studied with a primary focus on developing steady-state heat transfer correlations for porous media comprising different particulate solid with water being the interstitial fluid. Results show that heat transfer coefficients can be adequately determined via a Darcy-based model, and our results confirm a correlation proposed by Bejan [1]. It is speculated that the reason that the Darcy model works well in the present case is that the porous medium has a lower effective Prandtl number near the wall than in the bulk medium. The factors that contribute to this effects include the thinning of the boundary layer near the wall and an increase of effective thermal conductivity.
9
Jiang, Peixue, Yu Zhang et Runfu Shi. « Experimental and Numerical Investigation of Convection Heat Transfer of CO2 at Super-Critical Pressures in a Vertical Mini Tube ». Dans ASME 4th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2006. http://dx.doi.org/10.1115/icnmm2006-96110.
Texte intégralRésumé :
Convection heat transfer of CO2 at supercritical pressures in a 0.27mm diameter vertical mini tube was investigated experimentally and numerically. The tests investigated the effects of inlet temperature, pressure, mass flow rate, heat flux, buoyancy and flow direction on the convection heat transfer. The experimental results indicate that for inlet Reynolds numbers exceeding 4000, the flow direction and buoyancy force have little influence on the local wall temperature, with no deterioration of the convection heat transfer observed in either flow direction. The convection heat transfer coefficient initially increases with increasing heat flux and then decreases with further increases in the heat flux for both upward and downward flows. These effects are due to the variation of the thermophysical properties, especially cp. For inlet Reynolds numbers less than 2900, the local wall temperature varies nonlinearly for both flow directions. The numerical results correspond well with the experimental data for inlet Reynolds numbers exceeding 4000 using several turbulence models, especially the Realizable k-ε turbulence model. However, for inlet Reynolds numbers less than 2900, none of the turbulence models could properly simulate the convection heat transfer at super-critical pressures with high heat fluxes.
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BRUSSTAR, MATTHEW, et HERMAN MERTE, JR. « The effects of buoyancy on the critical heat flux in forced convection ». Dans 31st Aerospace Sciences Meeting. Reston, Virigina : American Institute of Aeronautics and Astronautics, 1993. http://dx.doi.org/10.2514/6.1993-575.
Texte intégralRapports d'organisations sur le sujet "Buoyancy fluxe"
1
Koseff, Jeffrey R., Joel H. Ferziger et Stephen G. Monismith. Turbulence Modeling in Stratified Flows Subject to Advective Buoyancy Fluxes. Fort Belvoir, VA : Defense Technical Information Center, septembre 2003. http://dx.doi.org/10.21236/ada618364.
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