Internal gravity waves generated by convective plumes

Ansong, Joseph K.; Sutherland, Bruce

doi:10.1017/s0022112009993193

Cited by 51 publications

(62 citation statements)

References 73 publications

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“…This result is consistent with the theory first proposed by Kotsovinos (2000), and with observations by Ansong et al (2008) of fountains in stationary ambients and by Ansong & Sutherland (2010) of buoyant plumes in a uniformly stratified environment. Upstream currents were not measured because of difficulty in distinguishing their fronts from the upward flow of the fountain.…”

Section: One-layer Experimentssupporting

confidence: 93%

“…However, there was no obvious relationship between this speed and the parameters of the experiment as was found for fountains and plumes in stationary environments (Ansong et al 2008;Ansong & Sutherland 2010). The propagation of gravity currents arising from fountains in both one-and twolayer environments requires further investigation, particularly as these are relevant to the motivating problem of understanding pollutant dispersion in the presence of an atmospheric inversion.…”

Section: Discussionmentioning

confidence: 90%

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Turbulent fountains in one- and two-layer crossflows

2011

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The Lagrangian theory developed for fountains in a stationary fluid is extended to predict the path and breadth of a fountain in a one-and two-layer fluid with a moderate crossflow. The predictions compare well with the results of laboratory experiments of fountains in a one-layer fluid. The empirical spreading parameter determined from the one-layer experiments is used in the theory for fountains in a twolayer crossflow. Though qualitatively correct, the theory underpredicts the height and radius of the fountains. Similar to the behaviour of fountains in two-layer stationary ambients, the fountain in a two-layer crossflow is observed to exhibit three regimes of flow: it may penetrate the interface, eventually returning to the level of the source where it spreads as a propagating gravity current; upon descent, it may be trapped at the interface where it spreads as a propagating intrusion; it may do both, partially descending to the source and partially being trapped at the interface. These regimes are classified theoretically and empirically. The theoretical classification compared the buoyancy excess of the descending flow to the density difference between the two layers. The regimes are also classified using empirically determined regime parameters which govern the relative initial momentum of the fountain and the relative density difference of the fountain and the ambient fluid.

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Section: One-layer Experimentssupporting

confidence: 93%

Section: Discussionmentioning

confidence: 90%

Turbulent fountains in one- and two-layer crossflows

2011

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“…The dimensionless Coriolis parameter is defined by [15], in which only ∼ 4% of the flow energy was transferred to internal waves. This contrasts with other flows, such as intrusions generated by a sudden collapse of mixed fluid, in which internal waves can play a more significant role [9].…”

Section: Shallow Layer Modelmentioning

confidence: 99%

Sustained axisymmetric intrusions in a rotating system

Ungarish

Johnson

Hogg

2016

European Journal of Mechanics - B/Fluids

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We analyse the effects of rotation on the propagation of an axisymmetric intrusion through a linearly stratified ambient fluid, arising from a sustained source at the level of neutral buoyancy. This scenario occurs during the horizontal spreading of a large volcanic ash cloud, which occurs after the plume has risen to its neutral buoyancy level. A simple and well-accepted approximation for the flow at late times is that inertial effects are negligible. This leads to a lensshaped intrusion governed by a balance between Coriolis accelerations and horizontal pressure gradients, with a radius scaling with time as r N ∼ t 1/3 . However, we show using shallow-layer model that inertial forces cannot be neglected until significant times after the beginning of the influx. These inertial forces result in the flow forming two distinct domains, separated by a moving hydraulic jump: an outer 'head' region in which the radial velocity and thickness vary with time, and a thinner 'tail' region in which the flow is steady. Initially, the flow expands rapidly and this tail region occupies most of the flow. After about one half-revolution of the system, Coriolis accelerations halt the advance of the front, and the hydraulic jump separating the two regions propagates back towards the source of the intrusion. Only after approximately one and a half rotations of the system does inertia become insignificant and the Coriolis lens solution, with r N ∼ t 1/3 , become established. Importantly, this means that neither inertia nor Coriolis accelerations can be neglected when modelling intrusions from volcanic eruptions. We exploit the two-region flow structure to construct a new hybrid model, comprising just two ordinary differential equations for the intrusion radius and location of the hydraulic jump.This hybrid model is much simpler than the shallow-layer model, but nonetheless accurately predicts flow properties such as the intrusion radius at all stages of motion, without requiring fitted or adjustable parameters.

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“…Mixing, in turn, makes the fluid in the counterflow lighter than the lower layer of stratification, so that it bounces back to the thermocline where it finally spreads at the level of neutral buoyancy. This structure is characteristic of a two-layer stratification (Cotel et al 1997;Ansong et al 2005) as compared to fountains in homogeneous and linearly stratified media, where the counterflow simply protrudes to the bed or to the level of neutral buoyancy (Bloomfield and Kerr 1998).…”

Section: Resultsmentioning

confidence: 99%

“…The oscillatory dynamics of fountains in stratified fluids is, however, mostly unexplored. Interestingly, the only experimental investigation in a linear stratification has shown no direct connection between the frequency of the fountain oscillations and the frequency of internal waves (Ansong and Sutherland 2010).…”

Section: Introductionmentioning

confidence: 99%

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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Internal gravity waves generated by convective plumes

Cited by 51 publications

References 73 publications

Turbulent fountains in one- and two-layer crossflows

Turbulent fountains in one- and two-layer crossflows

Sustained axisymmetric intrusions in a rotating system

Interaction between a Vertical Turbulent Jet and a Thermocline

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