Abstract
Turbulent buoyant plumes moving through density stratified environments transport large volumes of fluid vertically. Eventually, the fluid reaches its neutral buoyancy level at which it intrudes into the environment. For single-phase plume, the well-known theory of Morton, Taylor and Turner (Morton BR, Taylor GI, Turner JS. 1956 Turbulent gravitational convection from maintained and instantaneous sources. Proc. R. Soc. A 234, 1–23. (doi:10.1098/rspa.1956.0011)) describes the height of the intrusion with great accuracy. However, in multiphase plumes, such as descending particle plumes formed from the surface vessel during deep-sea mining operations, or ascending volcanic plumes, consisting of hot gas and dense ash particles, the sedimentation of particles can change the buoyancy of the fluid very significantly. Even if the plume speed far exceeds the sedimentation speed, the ultimate intrusion height of the fluid may be significantly affected by particle sedimentation. We explore this process, illustrating the phenomena with a series of analogue experiments and some simple modelling, and we discuss the applications in helping to quantify some environmental impacts of deep-sea mining and in helping to assess the eruption conditions leading to the formation of large laterally spreading ash clouds in the atmosphere.This article is part of the theme issue ‘Stokes at 200 (part 2)’.
Highlights
Turbulent plumes are produced by the release of buoyant fluid from a localized source
The particle-laden fluid is supplied through a localized nozzle of an internal diameter 1 mm, which is either located at the top of the tank in the case of a pure particle plume, or at the base of the tank in the case of a buoyant plume of fresh water, laden with particles, which provides a simplified model of the buoyant part of a volcanic eruption column
We have demonstrated that even if the particle fall speed is much smaller than the characteristic speed of royalsocietypublishing.org/journal/rsta Phil
Summary
Turbulent plumes are produced by the release of buoyant fluid from a localized source. Improving our understanding of the controls on the height and dynamics of these intrusions is valuable for the assessment of the hazards of volcanic ash, for air-traffic safety In this context, it is important to note that there are several very detailed numerical models of the eruption column and umbrella cloud which have been developed to account for effects of buoyancy-driven spreading of the umbrella cloud [16,17,18] and in some cases the effect of wind on the eruption column and neutral cloud [12,13,19]. The main emphasis of these papers was related to the height of rise of the plume, as well as aspects of the re-entrainment of the particles into the plume They did not explore the change in buoyancy of the radially intruding fluid supplied by the plume as a result of the sedimentation of the particles. We explore the interaction of the stratification in the ambient with the particleladen buoyant plume, and the role of the particle–fluid separation in influencing the intrusion height of the fluid above the plume
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