The entrainment due to a turbulent fountain at a density interface

Lin, Yi Hung; Linden, P. F.

doi:10.1017/s002211200500635x

Cited by 50 publications

(74 citation statements)

References 23 publications

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“…For Ri 1, the entrainment rate has been found to vary like Ri −3/2 , whereas for moderate Ri the entrainment rate decreases like Ri −1 (e.g. Turner, 1973, p. 294;Lin and Linden, 2005) and tends to a constant as Ri → 0 (e.g. Lin and Linden, 2005).…”

Section: Entrainment In Stratocumulusmentioning

confidence: 99%

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Droplet growth in warm turbulent clouds

Devenish

Bartello

Brenguier

et al. 2012

Quart J Royal Meteoro Soc

245

281

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In this survey we consider the impact of turbulence on cloud formation from the cloud scale to the droplet scale. We assess progress in understanding the effect of turbulence on the condensational and collisional growth of droplets and the effect of entrainment and mixing on the droplet spectrum. The increasing power of computers and better experimental and observational techniques allow for a much more detailed study of these processes than was hitherto possible. However, much of the research necessarily remains idealized and we argue that it is those studies which include such fundamental characteristics of clouds as droplet sedimentation and latent heating that are most relevant to clouds. Nevertheless, the large body of research over the last decade is beginning to allow tentative conclusions to be made. For example, it is unlikely that small-scale turbulent eddies (i.e. not the energy-containing eddies) alone are responsible for broadening the droplet size spectrum during the initial stage of droplet growth due to condensation. It is likely, though, that small-scale turbulence plays a significant role in the growth of droplets through collisions and coalescence. Moreover, it has been possible through detailed numerical simulations to assess the relative importance of different processes to the turbulent collision kernel and how this varies in the parameter space that is important to clouds. The focus of research on the role of turbulence in condensational and collisional growth has tended to ignore the effect of entrainment and mixing and it is arguable that they play at least as important a role in the evolution of the droplet spectrum. We consider the role of turbulence in the mixing of dry and cloudy air, methods of quantifying this mixing and the effect that it has on the droplet spectrum. Copyright

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Section: Entrainment In Stratocumulusmentioning

confidence: 99%

“…Turner, 1973, p. 294;Lin and Linden, 2005) and tends to a constant as Ri → 0 (e.g. Lin and Linden, 2005). When the distortion of the interface is taken into account, Mahrt (1979) suggests that the entrainment rate associated with the horizontal and vertical components of the entrainment velocity may differ.…”

Section: Entrainment In Stratocumulusmentioning

confidence: 99%

Droplet growth in warm turbulent clouds

Devenish

Bartello

Brenguier

et al. 2012

Quart J Royal Meteoro Soc

245

281

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“…Firstly, it drains through the top opening as a continuation of the upward ventilation flow. Secondly, the continuing turbulent plume may entrain some of the upper-layer fluid since, although it is relatively dense, it can overshoot the interface, thereby mixing with some of the original upper-layer fluid, before falling back into the lower layer (Baines 1975;Baines, Turner & Campbell 1990;Bloomfield & Kerr 2000;Linden 1973;Kumagai 1984;Lin & Linden 2005;McDougall 1981). We refer to this regime as the 'intruding' regime.…”

Section: Introductionmentioning

confidence: 99%

Transient ventilation dynamics following a change in strength of a point source of heat

Bower¹,

Caulfield

Fitzgerald³

et al. 2008

J. Fluid Mech.

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We investigate the transient ventilation flow within a confined ventilated space, with high-and low-level openings, when the strength of a low-level point source of heat is changed instantaneously. The steady-flow regime in the space involves a turbulent buoyant plume, which rises from the point source to a well-mixed warm upper layer. The steady-state height of the interface between this layer and the lower layer of exterior fluid is independent of the heat flux, but the upper layer becomes progressively warmer with heat flux. New analogue laboratory experiments of the transient adjustment between steady states identify that if the heat flux is increased, the continuing plume propagates to the top of the room forming a new, warmer layer. This layer gradually deepens, and as the turbulent plume entrains fluid from the original warm layer, the original layer is gradually depleted and disappears, and a new steady state is established. In contrast, if the source buoyancy flux is decreased, the continuing plume is cooler than the original plume, so that on reaching the interface it is of intermediate density between the original warm layer and the external fluid. The plume supplies a new intermediate layer, which gradually deepens with the continuing flow. In turn, the original upper layer becomes depleted, both as a result of being vented through the upper opening of the space, but also due to some penetrative entrainment of this layer by the plume, as the plume overshoots the interface before falling back to supply the new intermediate layer. We develop quantitative models which are in good accord with our experimental data, by combining classical plume theory with models of the penetrative entrainment for the case of a decrease in heating. Typically, we find that the effect of penetrative entrainment on the density of the intruding layer is relatively weak, provided the change in source strength is sufficiently large. However, penetrative entrainment measurably increases the rate at which the depth of the draining layer decreases. We conclude with a discussion of the importance of these results for the control of naturally ventilated spaces.

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“…This important question has been before investigated for a jet in two-layer stratification with a density interface experimentally (Cotel et al 1997;Lin and Linden 2005) and theoretically (Shrinivas andHunt 2014, 2015). In this study, we investigate the mean flows in the thermocline and compare the entrainment flux of the jet in stratifications characterized by a finite thickness of the thermocline with the results of the theoretical model by Shrinivas and Hunt (2014).…”

Section: Introductionmentioning

confidence: 93%

Interaction between a Vertical Turbulent Jet and a Thermocline

Ezhova

Cenedese

Brandt

2016

Journal of Physical Oceanography

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The behavior of an axisymmetric vertical turbulent jet in an unconfined stratified environment is studied by means of well-resolved, large-eddy simulations. The stratification is two uniform layers separated by a thermocline. This study considers two cases: when the thermocline thickness is small and on the order of the jet diameter at the thermocline entrance. The Froude number of the jet at the thermocline varies from 0.6 to 1.9, corresponding to the class of weak fountains. The mean jet penetration, stratified turbulent entrainment, jet oscillations, and the generation of internal waves are examined. The mean jet penetration is predicted well by a simple model based on the conservation of the source energy in the thermocline. The entrainment coefficient for the thin thermocline is consistent with the theoretical model for a two-layer stratification with a sharp interface, while for the thick thermocline entrainment is larger at low Froude numbers. The data reveal the presence of a secondary horizontal flow in the upper part of the thick thermocline, resulting in the entrainment of fluid from the thermocline rather than from the upper stratification layer. The spectra of the jet oscillations in the thermocline display two peaks, at the same frequencies for both stratifications at fixed Froude number. For the thick thermocline, internal waves are generated only at the lower frequency, since the higher peak exceeds the maximal buoyancy frequency. For the thin thermocline, conversely, the spectra of the internal waves show the two peaks at low Froude numbers, whereas only one peak at the lower frequency is observed at higher Froude numbers.

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The entrainment due to a turbulent fountain at a density interface

Cited by 50 publications

References 23 publications

Droplet growth in warm turbulent clouds

Droplet growth in warm turbulent clouds

Transient ventilation dynamics following a change in strength of a point source of heat

Interaction between a Vertical Turbulent Jet and a Thermocline

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