Turbulent plumes, such as the BP oil plume in the Gulf of Mexico or the Icelandic volcanic plume, can mix and carry large quantities of fluid from the surrounding atmosphere or ocean. The process of mixing is called entrainment, and is determined by the turbulent shear stresses, buoyancy forces, and the similarity drift of the radial distributions of velocity and buoyancy in the plume.
Multiphase plumes have both continuous and discrete phases, which may interact through dissolution, phase-change and reaction processes. For example, in the BP oil plume gaseous methane and liquid oil dissolved into seawater. Additionally, methane reacted with seawater to produce hydrates. The presence of droplets and/or bubbles may also modulate turbulence levels in the plume. All these internal processes affect the motion and entrainment into the plume.
New theoretical and experimental work in the Fluids and Environment Group, published recently in the Journal of Fluid Mechanics , has determined the rate of entrainment of external fluid into a multiphase plume. The contributions from shear, buoyancy and similarity drift of profiles are measured for inert plumes, as well as for plumes with reaction or phase change. This research has implications for the understanding of the behaviour of large-scale plumes, such as the BP oil plume and the Icelandic volcanic plume, and their impact on our environment. The work can also help us predict the motion of a potential leak of carbon dioxide from storage in saline aquifers under the sea bed - one of the many methods being explored to mitigate rising CO2 levels in the atmosphere. The work was funded by the Royal Society and the Cambridge Gates Trust.
Image: A turbulent multiphase, reacting plume rising in a uniform environment (left) and corresponding flow field (right). The turbulent eddies, responsible for the irregular edge of the plume, drive entrainment of external fluid into the plume. This mixing causes radial expansion.