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During undersea oil blowout in crossflow conditions, the oil droplets entrained horizontally which increased the residence time of droplets in the water column. Knowledge of the trajectory of an oil plume is important for predicting the pathways of hydrocarbons and to devise countermeasures. We conducted large-scale experiments in the Ohmsett tank where we released oil from a one-inch vertical orifice that was towed to produce the behavior of a jet in crossflow. The average oil velocity at the orifice was 1.36 m/s and the crossflow velocity was around 0.27 m/s which resulted in a jet-to-crossflow velocity ratio of 5.0. The results were simulated numerically using the Large Eddy Simulation (LES) turbulence model and the mixture multiphase model within the open-source software OpenFOAM. The instruments including ADVs, LISSTs, shadowgraph cameras, holographic camera, and fluorometers were employed. The oil jet released from the nozzle started to meander in the vertical direction most probably due to weak crossflow. The trajectory and meandering behavior of the oil jet, wavy pattern along the leading edge of the jet and column breakup observed in the experiments were captured well with the numerical simulation. The surface breakup just above the orifice created ligaments and droplets downstream of the jet. Larger oil droplets were observed near the upper boundary of the plume due to their higher buoyancy while the smaller droplets were suspended in the water column and they were entrained by water crossflow. This work reveals that different size of droplets determines the overall shape of plumes mostly the upper and lower boundaries of the plume.

This paper presents the details of a numerical model that is capable of simulating the droplet size distribution emanating from blowouts. The model was obtained as a result of combination of traditional mechanistic models developed in reactors with jet (or plume) models to predict the evolution of the plume away from the orifice. Inputs to the model include the energy dissipation rate (or the mixing energy) and holdup, which is the volume fraction of oil in the control volume. These parameters vary as the plume spreads away from the orifice. They have a maximum value near the orifice and rapidly decrease as moving away from the orifice. The model was validated using experimental data available in the literature. Subsequently, the model was used to predict the evolution of droplets in the Deepwater Horizon incident. The model provides the variation of the mean diameter and the droplet size distribution with depths away from the orifice. The sensitivity of different parameters, such as interfacial tension which could present the addition of dispersants was also evaluated.

As part of the response to the BP Deepwater Horizon spill in 2010, we have been funded by the Gulf of Mexico Research Initiative to construct a nested model suite that can follow an oil particle from its first release to its arrival on a shoreline, taking into account natural rates of mixing and degradation of the oil components. The model suite incorporates (at increasing levels of resolution) a coupled ocean-atmosphere model of the full Gulf of Mexico and North Atlantic Ocean, a deep Gulf of Mexico model, a regional model of the Texas-Louisiana shelf, a 3D, non-hydrostatic bay model, a 3D Navier-Stokes model of the spill plume, and a particle tracking and transformation model for dispersed and dissolved oil and gas fate and transport integrated within the full flow domain. The models are supported by a series of laboratory and field experiments, including studies of single droplets, with and without dispersant, plumes, a deep-sea tracer release experiment and bubble releases to simulate an underwater blowout. The laboratory experiments will improve modeling of small-scale, near-field processes such as bubble and droplet formation, dissolution, droplet-turbulence interaction, and evaporation and dispersion at the air-sea interface. We show how the models are linked and how we are making progress towards the complete nested model suite, which will be available for use in future spills.