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

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.