Dynamics of multiphase turbulent plumes with hybrid buoyancy sources in stratified environments

Abstract

Deepwater oil blowouts typically generate multiphase hybrid plumes where the total inlet buoyancy flux is set by the combined presence of gas, oil, and heat. We numerically investigate the effects of combined sources of inlet buoyancy on turbulent plume dynamics by varying the inputs of a dispersed, slipping gas phase and a non-slipping buoyant liquid phase in thermally stratified environments. The ability of a single momentum equation, multiphase model to correctly reproduce characteristic plume heights is validated for both dispersed liquid phase and pure gas bubble plumes. A hybrid case, containing buoyancy contributions from both gas and liquid phases, is also investigated. As expected, on the plume centerline, the presence of a slipping gas phase increases both the vertical location of the neutrally buoyant equilibrium height and the maximum vertical extent of the liquid effluent relative to non-bubble plumes. While producing an overall increase in the plume height, the presence of a slipping gas phase also significantly enhances both the extent and magnitude of negatively buoyant downdrafts in the outer plume region. As a result, the intrusion or trapping height, the vertical distance where liquid phase plume effluent accumulates, is found to be significantly lower in both bubble and hybrid plumes. Below the intrusion level, the simulations are compared to an integral model formulation that explicitly accounts for the effects of the gas slip velocity in the evolution of the buoyancy flux. Discrepancies in the integral model and full solutions are largest in the source vicinity region where vertical turbulent volume fluxes, necessarily neglected in the integral formulation, are significant.

Numerical simulations of rotating bubble plumes in stratified environments

“…In the absence of rotation, the presence of a slipping gas phase also produces lowering and thickening of the primary lateral intrusion layer (Figures a, d, and g) due to enhancement of the recirculating downdrafts and increased turbulent mixing [ Fabregat et al ., ]. The dramatic difference in the distribution of β between the and cases is consistent with a change in the topological classification from Type 1 to Type 2 bubble plumes [ Asaeda and Imberger , ; Socolofsky and Adams , ].…”

“…[] and further investigated in stratified environments by Fabregat et al . []. The primary assumptions are (i) Boussinesq flow (density variations only accounted in the buoyancy term) and (ii) due to the considerable difference in density, the gas phase carries a negligible amount of momentum compared to the liquid phase [ Sokolichin et al ., ].…”

“…The mesh is identical to the one reported in Fabregat et al . [] for rotating single‐phase plumes. The boundary conditions are also the same, i.e., Dirichlet at the bottom where the inlet is defined with constant values, no‐shear at the top for the momentum and zero derivative for the scalars.…”

“…Numerical stability at these open boundaries is ensured using numerical sponge regions [ Applequist and Schlatter , ] where local diffusivity coefficients for momentum and scalars smoothly increase to damp arriving perturbations. Grid and lateral boundary sensitivity analysis suggest that mesh resolution and domain size have negligible impact on the solution [ Fabregat et al ., ].…”

“…In the absence of interphase mass transfer, the model is equivalent to that used by Alendal and Drange [] to model oceanic carbon sequestration. The primary role of the slip velocity on the plume topology, investigated in bubble plume experiments by Asaeda and Imberger [] and Socolofsky and Adams [] over a range of parameter values, is correctly reproduced by the model in numerical simulations [ Fabregat et al ., ].…”