We numerically investigate the effects of rotation on the turbulent dynamics of thermally driven buoyant plumes in stratified environments at the large Rossby numbers characteristic of deep oceanic releases. When compared to nonrotating environments, rotating plumes are distinguished by a significant decrease in vertical buoyancy and momentum fluxes leading to lower and thicker neutrally buoyant intrusion layers. The primary dynamic effect of background rotation is the concentration of entraining fluid into a strong cyclonic flow at the base of the plume resulting in cyclogeostrophic balance in the radial momentum equation. The structure of this cyclogeostrophic balance moving upward from the well head is associated with a net adverse vertical pressure gradient producing an inverted hydrostatic balance in the mean vertical momentum budgets. The present simulations reveal that the primary response to the adverse pressure gradient is an off‐axis deflection of the plume that evolves into a robust, organized anticyclonic radial precession about the buoyancy source. The off‐axis evolution is responsible for the weaker inertial overshoots, the increased thickness of lateral intrusion layers, and the overall decrease in the vertical extent of rotating plumes at intermediate Rossby numbers compared to the nonrotating case. For inlet buoyancy forcings and environmental Rossby numbers consistent with those expected in deepwater blowout plumes, the speed of the organized precession is found to be as large as typical oceanic cross‐flow speeds.
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.
The effects of system rotation on the turbulent dynamics of bubble plumes evolving in stratified environments are numerically investigated by considering variations in both the system rotation rate and the gas‐phase slip velocity. The turbulent dispersion of a passive scalar injected at the source of a buoyant plume is strongly altered by the rotation of the system and the nature of the buoyancy at the source. When the plume is driven by the density defect associated with the presence of slipping gas bubbles, the location of the main lateral intrusion decreases with respect to the single‐phase case with identical inlet volume, momentum, and buoyancy fluxes. Enhanced downdrafts of carrier phase fluid result in increased turbulent mixing and short‐circuiting of detraining plume water that elevate near‐field effluent concentrations. Similarly, rotation fundamentally alters dynamic balances within the plume leading to the encroachment of the trapping height on the source and an increase in turbulent dispersion in the near field. System rotation, even at modest Rossby numbers, produces a sustained, robust, anticyclonic precession of the plume core. The effects of rotation and the presence of bubbles are cumulative. The vertical encroachment of the primary intrusion and the overall dispersion of effluent are greatest at smallest Rossby numbers and largest slip velocities. The main characteristic feature in rotating single‐phase plumes, namely the robust anticyclonic precession, persists in bubble plumes. Analysis of the momentum budgets reveal that the mechanism responsible for the organized precession, i.e., the establishment of an unstable vertical hydrostatic equilibrium related to radial cyclostrophic balance, does not differ from the single‐phase case.
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