Enhanced ablation of a vertical ice wall due to an external freshwater plume

2016 ◽  
Vol 810 ◽  
pp. 429-447 ◽  
Author(s):  
Craig D. McConnochie ◽  
Ross C. Kerr
Keyword(s):  
Laboratory Experiments ◽  
Buoyancy Flux ◽  
Interface Temperature ◽  
Volume Flux ◽  
Salty Water ◽  
Plume Velocity ◽  
Freshwater Plume ◽  
Wall Plume

We investigate the effect of an external freshwater plume on the dissolution of a vertical ice wall in salty water using laboratory experiments. We measure the plume velocity, the ablation velocity of the ice and the temperature at the ice wall. The freshwater volume flux, $Q_{s}$, is varied between experiments to determine where the resultant wall plume transitions from being dominated by the distributed buoyancy flux due to dissolution of the ice, to being dominated by the initial buoyancy flux, $B_{s}$. We find that when $B_{s}$ is significantly larger than the distributed buoyancy flux from dissolution, the plume velocity is uniform with height and is proportional to $B_{s}^{1/3}$, the interface temperature is independent of $B_{s}$, and the ablation velocity increases with $B_{s}$.

The effect of a salinity gradient on the dissolution of a vertical ice face

2016 ◽  
Vol 791 ◽  
pp. 589-607 ◽  
Author(s):  
Craig D. McConnochie ◽  
Ross C. Kerr
Keyword(s):  
Unit Area ◽  
Salinity Gradient ◽  
Ice Sheets ◽  
Interface Temperature ◽  
Volume Flux ◽  
Ice Shelves ◽  
Ocean Stratification ◽  
Salinity Gradients ◽  
Plume Velocity ◽  
The Antarctic

We investigate experimentally the effect of stratification on a vertical ice face dissolving into cold salty water. We measure the interface temperature, ablation velocity and turbulent plume velocity over a range of salinity gradients and compare our measurements with results of similar experiments without a salinity gradient (Kerr & McConnochie, J. Fluid Mech., vol. 765, 2015, pp. 211–228; McConnochie & Kerr, J. Fluid Mech., vol. 787, 2016, pp. 237–253). We observe that stratification acts to reduce the ablation velocity, interface temperature, plume velocity and plume acceleration. We define a stratification parameter, $S=N^{2}Q/{\it\Phi}_{o}$, that describes where stratification will be important, where $N$ is the Brunt–Väisälä frequency, $Q$ is the height-dependent plume volume flux and ${\it\Phi}_{o}$ is the buoyancy flux per unit area without stratification. The relevance of this stratification parameter is supported by our experiments, which deviate from the homogeneous theory at approximately $S=1$. Finally, we calculate values for the stratification parameter at a number of ice shelves and conclude that ocean stratification will have a significant effect on the dissolution of both the Antarctic and Greenland ice sheets.

Quasi-steady states in natural displacement ventilation driven by periodic gusting of wind

2012 ◽  
Vol 707 ◽  
pp. 1-23 ◽  
Author(s):  
Richard W. Mott ◽  
Andrew W. Woods
Keyword(s):  
Laboratory Experiments ◽  
Temporal Variations ◽  
The Body ◽  
Buoyancy Flux ◽  
Shopping Mall ◽  
Displacement Ventilation ◽  
Geometric Properties ◽  
Two Layer Model ◽  
High Level ◽  
Continuous Source

AbstractWe investigate the natural displacement ventilation of a space connected to a body of warm fluid through high- and low-level vents. The space is subject to discrete periodic gusts of wind entering at high level from a cold exterior. The cold exterior air entering the space produces buoyancy differences between the space and the body of warm fluid, driving a ventilation flow. Initially we examine the case of a series of identical gusts of wind modelled as turbulent buoyant thermals. New laboratory experiments show that an approximately two-layer stratification is established and the height of the interface is quasi-steady if the period between thermals is much less than the draining time of the space but longer than the fall time of individual thermals. Experiments also show that the interface height depends on the average buoyancy flux associated with the wind gusts, the time between thermals as well as the geometric properties of the vents. This contrasts with the case of a continuous source of buoyancy where the interface height depends only on the geometric properties of the vents and is independent of the buoyancy flux. We develop a quasi-steady two-layer model of the flow based on the classical theory of turbulent thermals and show that it is consistent with our new experimental data. We generalize the model to explore the sensitivity of the results to temporal variations in the size of thermals. We then extend the model to explore the effects of longer interval times between successive thermals and find a two-layer stratification still develops but that the interface height now varies cyclically in time. We then discuss the implications of these results for the ventilation of a shopping mall subject to gusts of wind.

The turbulent wall plume from a vertically distributed source of buoyancy

2015 ◽  
Vol 787 ◽  
pp. 237-253 ◽  
Author(s):  
Craig D. McConnochie ◽  
Ross C. Kerr
Keyword(s):  
Theoretical Model ◽  
Reynolds Numbers ◽  
Vertical Surface ◽  
Distributed Source ◽  
Plume Model ◽  
Plume Velocity ◽  
Entrainment Coefficient ◽  
Turbulent Plume ◽  
Turbulent Wall ◽  
Wall Plume

We experimentally investigate the turbulent wall plume that forms next to a uniformly distributed source of buoyancy. Our experimental results are compared with the theoretical model and experiments of Cooper & Hunt (J. Fluid Mech., vol. 646, 2010, pp. 39–58). Our experiments give a top-hat entrainment coefficient of $0.048\pm 0.006$. We measure a maximum vertical plume velocity that follows the scaling predicted by Cooper & Hunt but is significantly smaller. Our measurements allow us to construct a turbulent plume model that predicts all plume properties at any height. We use this plume model to calculate plume widths, velocities and Reynolds numbers for typical dissolving icebergs and ice fronts and for a typical room with a heated or cooled vertical surface.

Source and boundary condition effects on unconfined and confined vertically distributed turbulent plumes

2018 ◽  
Vol 850 ◽  
pp. 1032-1065 ◽  
Author(s):  
N. B. Kaye ◽  
P. Cooper
Keyword(s):  
Volume Flow Rate ◽  
Volume Flow ◽  
Buoyancy Flux ◽  
Boundary Effects ◽  
Volume Flux ◽  
Distributed Source ◽  
Physical Geometry ◽  
Self Similar ◽  
The Mean ◽  
The Impact

Plumes generated by vertically distributed sources of buoyancy have been observed to have substantially lower entrainment coefficients than their equivalent-geometry constant buoyancy flux plumes. Two differences between distributed and localized sources of buoyancy are the presence of a wall shear stress at the source and that non-ideal source conditions are distributed over the whole height of the enclosure for a vertically distributed source. Herein the impact of non-ideal source and boundary conditions on vertically distributed plumes is analysed. It is shown that, at small heights, the plume volume flow rate is significantly influenced by the wall-source volume flux. At larger heights the wall-source buoyancy is greater than the mean plume buoyancy, creating a non-self-similar horizontal buoyancy distribution within the plume. Recent experiments into the behaviour of a vertically distributed source of buoyancy in a confined region have also shown that the plume partially detrains in the stratified region of the enclosure. This detrainment has not been observed for constant buoyancy flux plumes in a confined region. Although models have been proposed to quantify the detrainment process, it is still unclear why vertically distributed buoyancy sources detrain while constant buoyancy flux plumes do not in the same physical geometry. The impact of source and boundary effects on previously published experiments on vertically distributed plumes are reviewed and the possible implications for plume entrainment and detrainment are discussed.

scholarly journals Entrainment in two coalescing axisymmetric turbulent plumes

2014 ◽  
Vol 752 ◽  
Author(s):  
C. Cenedese ◽  
P. F. Linden
Keyword(s):  
Large Scale ◽  
Laboratory Experiments ◽  
Dynamical Evolution ◽  
The Other ◽  
Volume Flux ◽  
Ambient Fluid ◽  
Plume Dynamics ◽  
Complex Models ◽  
Definition Of ◽  
Reduced Surface

AbstractA 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, $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\alpha _{eff}$, as the value of $\alpha $ needed to obtain the same total volume flux in two independent plumes as that occurring in two coalescing plumes. The definition of $\alpha _{eff}$ 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.

scholarly journals The Intrusion Depth of Density Currents Flowing into Stratified Water Bodies

2009 ◽  
Vol 39 (8) ◽  
pp. 1935-1947 ◽  
Author(s):  
Mathew Wells ◽  
Parthiban Nadarajah
Keyword(s):  
Water Column ◽  
Large Scale ◽  
Laboratory Experiments ◽  
Buoyancy Flux ◽  
Density Current ◽  
Density Currents ◽  
Coriolis Parameter ◽  
Entrainment Ratio ◽  
Geostrophic Balance ◽  
Intrusion Depth

Abstract Theory and laboratory experiments are presented describing the depth at which a density current intrudes into a linearly stratified water column, as a function of the entrainment ratio E, the buoyancy flux in the dense current B, and the magnitude of the stratification N. The main result is that Z ∼ E−1/3B1/3/N. It is shown that the depth of the intrusion scales as Z ∼ (3 ± 1)B1/3/N for laboratory experiments, and as for oceanic density currents. The velocity of a large-scale density current is controlled by a geostrophic balance defined as Ugeo = 0.25g′s/f, where s is the slope and f is the Coriolis parameter. The geostrophic buoyancy flux is then defined by Bgeo = g′Ugeoh, with g′ the reduced gravity and h the thickness of the current. The scaling herein implies that the depth of an oceanic intrusion is relatively insensitive to changes in source water properties but is very sensitive to changes in the stratification of the water column, consistent with the previous scaling of Price and Baringer. For example, if the buoyancy flux of a dense current were to double while the stratification remained constant, then there would only be a 25% increase in the intrusion depth, whereas doubling the stratification would result in a 50% decrease of the intrusion depth.

Temporal variation of non-ideal plumes with sudden reductions in buoyancy flux

2008 ◽  
Vol 600 ◽  
pp. 181-199 ◽  
Author(s):  
M. M. SCASE ◽  
C. P. CAULFIELD ◽  
S. B. DALZIEL
Keyword(s):  
Temporal Evolution ◽  
Buoyancy Flux ◽  
Passive Tracer ◽  
Volume Flux ◽  
Finite Radius ◽  
Previous Theory ◽  
Sudden Drop ◽  
Model Predictions ◽  
Theoretical Predictions ◽  
The Individual

We model the behaviour of isolated sources of finite radius and volume flux which experience a sudden drop in buoyancy flux, generalizing the previous theory presented in Scase et al. (J. Fluid Mech., vol. 563, 2006, p. 443). In particular, we consider the problem of the source of an established plume suddenly increasing in area to provide a much wider plume source. Our calculations predict that, while our model remains applicable, the plume never fully pinches off into individual rising thermals.We report the results of a large number of experiments, which provide an ensemble to compare to theoretical predictions. We find that provided the source conditions are weakened in such a way that the well-known entrainment assumption remains valid, the established plume is not observed to pinch off into individual thermals. Further, not only is pinch-off not observed in the ensemble of experiments, it cannot be observed in any of the individual experiments. We consider both the temporal evolution of the plume profile and a concentration of passive tracer, and show that our model predictions compare well with our experimental observations.

Abrupt Transitions and Hysteresis in Thermohaline Laboratory Models

2009 ◽  
Vol 39 (5) ◽  
pp. 1231-1243 ◽  
Author(s):  
J. A. Whitehead
Keyword(s):  
Ocean Circulation ◽  
Room Temperature ◽  
Laboratory Experiments ◽  
Internal Circulation ◽  
Abrupt Transition ◽  
Salty Water ◽  
Temperature Mode ◽  
Large Tank ◽  
History Of ◽  
Laboratory Models

Abstract As a driving parameter is slowly altered, thermohaline ocean circulation models show either a smooth evolution of a mode of flow or an abrupt transition of temperature and salinity fields from one mode to another. An abrupt transition might occur at one value or over a range of the driving parameter. The latter has hysteresis because the mode in this range depends on the history of the driving parameter. Although assorted ocean circulation models exhibit abrupt transitions, such transitions have not been directly observed in the ocean. Therefore, laboratory experiments have been conducted to seek and observe actual (physical) abrupt thermohaline transitions. An experiment closely duplicating Stommel’s box model possessed abrupt transitions in temperature and salinity with distinct hysteresis. Two subsequent experiments with more latitude for internal circulation in the containers possessed abrupt transitions over a much smaller range of hysteresis. Therefore, a new experiment with even more latitude for internal circulation was designed and conducted. A large tank of constantly renewed freshwater at room temperature had a smaller cavity in the bottom heated from below with saltwater steadily pumped in. The cavity had either a salt mode, consisting of the cavity filled with heated salty water with an interface at the cavity top, or a temperature mode, in which the heat and saltwater were removed from the cavity by convection. There was no measurable hysteresis between the two modes. Possible reasons for such small hysteresis are discussed.

Covering of cometary nucleus by refractory crust and its evolution into asteroid-like body

1999 ◽  
Vol 173 ◽  
pp. 365-370
Author(s):  
Kh.I. Ibadinov
Keyword(s):  
Laboratory Experiments ◽  
Cometary Nucleus ◽  
Sublimation Rate ◽  
Cometary Nuclei ◽  
Short Period Comet ◽  
Short Period ◽  
Brightness Decrease ◽  
Crust Thickness ◽  
Ice Sublimation ◽  
Period Comet

AbstractFrom the established dependence of the brightness decrease of a short-period comet dependence on the perihelion distance of its orbit it follows that part of the surface of these cometary nuclei gradually covers by a refractory crust. The results of cometary nucleus simulation show that at constant insolation energy the crust thickness is proportional to the square root of the insolation time and the ice sublimation rate is inversely proportional to the crust thickness. From laboratory experiments resulted the thermal regime, the gas productivity of the nucleus, covering of the nucleus by the crust, and the tempo of evolution of a short-period comet into the asteroid-like body studied.

When Does Voice Have to be More Than Only Listening? Procedural Justice Effects as a Function of Confident Leadership

2010 ◽  
Vol 9 (2) ◽  
pp. 69-78 ◽  
Author(s):  
David De Cremer ◽  
Maarten Wubben
Keyword(s):  
Procedural Justice ◽  
Interaction Effect ◽  
Laboratory Experiments ◽  
Negative Emotions

The present research examined how voice procedures and leader confidence affect participants’ negative emotions and willingness to withdraw. It was predicted that receiving voice would be valued out of instrumental concerns, but only when the enacting leader was high in confidence. Two laboratory experiments indeed showed an interaction between type of voice (pre-decisional vs. post-decisional) and leader’s confidence (low vs. high) on participants’ negative emotions and willingness to withdraw. In particular, post-decision voice only led to more negative responses than did pre-decision voice when the enacting leader was high in confidence. Negative emotions mediated this interaction effect of type of voice on willingness to withdraw. Implications for integrating the leadership and procedural justice literatures are discussed.

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