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Understanding the droplet size distribution of subsea oil releasing is important to predict the subsequent transport and degradation of the spilled oil. Single- and multi-phase oil jet experiments were conducted in the Ohmsett facility, including pure oil jet and oil-air jet through a 10.7-mm pipe and a 4.7-mm pipe. Measurements of the vertical jet hydrodynamics and the oil size distribution were obtained. The reported results help to extend subsea oil spills experiment scale into a meso-scale, and the measurement range of the oil size is widened up to 2 cm. Moreover, the application of dispersant and involvement of air phase provided valuable scientific evidence for the usage of dispersants to treat oil spills. The data confirmed the effectiveness of the dispersant that reduces oil droplet size and also suggested that the participation of the gas phase facilitated the decreasing of oil droplet size. The results were compared to the numerical simulation tool VDROP-J. While the hydrodynamics showed good consistency, the systemdependent coefficient needed a slight revision to coincide with presented data. This also confirmed the significance of experimental materials for further validation and development of oil spill models, where we also provided guidance and discussion on conducting and post-processing the oil spill experiment. [ABSTRACT FROM AUTHOR]

Microplastics pose a significant and growing threat to marine ecosystems and human health. Rivers serve as critical pathways for the entry of inland-produced microplastics into marine environments. In this paper, we developed a numerical modeling scheme using OpenFOAM to investigate the fate and transport of microplastics in a river system. Our simulation results show that microplastics undergo significant aggregation and breakage as they are transported downstream by river flows. This significantly alters the particle size distribution of microplastics. The aggregation-breakage process is mainly controlled by river hydrodynamics and pollution scale. Our findings suggest that a significant extent of particle aggregation occurs at an early stage of the release of microplastics in the river, while the aggregation-breakage process becomes limited as the microplastic plume is gradually dispersed and diluted downstream. Eddy diffusivity drives the dispersion of the microplastic plume in the river, and its spatial patterns affect the aggregation-breakage process. • River hydrodynamics affect the aggregation and breakage processes of microplastics. • Great extent of aggregation occurs at early stage of the release of microplastics. • Interplay between microplastic transport and aggregation-breakage occurs in rivers. [ABSTRACT FROM AUTHOR]

Jets and plumes have been the focus of quantitative investigations since the mid-1950s. These investigations intensified following the Deepwater Horizon oil spill, in which thousands of tons of oil and natural gas were released into the Gulf of Mexico. This review focuses on plume dynamics that apply to both single-phase and multiphase liquid-in-liquid and liquid plus gas into liquid plumes, including bubble and droplet formation, and heat and mass transfer. Broadly, our work highlights several previously unknown or overlooked aspects of multiphase flow in the deep oceans. Upstream of the jet release, multiphase hydraulics can significantly affect the turbulence, for instance, through churn flow that enhances the turbulence in the free jet, affecting the conditions where bubbles and droplets are formed. Droplet formation was a major focus recently, with experiments covering a range of scales and flow rates of oil and gas at low and high pressure. Detailed observations of droplet formation at the jet-water boundary reveal the formation of compound droplets, which are emulsions of oil and water with implications for mass conservation and mass transfer. At the plume scale, integral models have been adapted to include the complex thermodynamics and chemistry of oil and gas plumes. In parallel, significant advances were made in numerical simulations of multiphase plumes through large eddy simulations by treating the oil and gas either a continuous or discrete phase. Through this work, a vivid picture of the complex droplet, chemical, and hydrodynamic behavior of multiphase plumes in the ocean is emerging. [ABSTRACT FROM AUTHOR]

Abstract Theoretical arguments and numerical investigations were conducted to understand the transport of oil droplets under ice. It was found that the boundary layer (BL) in the water under ice produces a downward velocity that reaches up to 0.2% of horizontal current speed, and is, in general, larger than the rise velocity of 70 μm oil droplets. The eddy diffusivity was found to increase with depth and to decrease gradually afterward. Neglecting the gradient of eddy diffusivity when conducting Lagrangian transport of oil droplets would result in an unphysical spatial distribution. When the downward velocity of water was neglected, oil accumulated at the water-ice interface regardless of the attachment efficiency. The lift force was found to scrape off droplets of the ice, especially for droplets ≤ 70 μm. These findings suggest that previous oil spill simulations may have overestimated the number of small droplets (≤70 μm) at the water-ice interface. Highlights • A downward water velocity occurs under the ice due to boundary layer (BL) hydrodynamics. • The gradient of eddy diffusivity needs to be considered in Lagrangian oil spill models. • Lift at the ice-water interface could scrape off oil droplets of the ice. • The findings suggest existing approaches overestimate the amount of small oil droplet (< 70 μm) at the water-ice interface. [ABSTRACT FROM AUTHOR]

Modeling the movement of oil released underwater is a challenging task due to limitations in measuring the hydrodynamics in an oil-water system. In this work, we conducted an experiment of horizontal release of oil without and with dispersant. The model VDROP-J was used and compared to the model JETLAG, a miscible plume trajectory model. Both models were found to reproduce the oil jet hydrodynamics for oil without and with dispersant. The predicted DSD from VDROP-J matched closely observation for untreated oil. For oil with dispersant, experimental results have shown evidence that tip streaming occurred. For this purpose, a new conceptual module was developed in VDROP-J to capture the tip streaming phenomenon and an excellent match was achieved with observation. This study is the first to report tip streaming occurring in underwater oil jets, which should have consequences on predicting the DSD when dispersant are used on an underwater oil release. © 2017 American Institute of Chemical Engineers AIChE J, 2017 [ABSTRACT FROM AUTHOR]

The interaction of oil and sediment in the environment determines, to a large extent, the trajectory and fate of oil. Using confocal microscope imaging techniques to obtain detailed 3D structures of oil-particle aggregates (OPAs) formed in turbulent flows, we elucidated a new mechanism of particle attachment, whereby the particles behave as projectiles penetrating the oil droplets to depths varying from ~2 to 10 µm due to the hydrodynamic forces in the water. This mechanism results in a higher attachment of particles on oil in comparison with adsorption, as commonly assumed. The projectile hypothesis also explains the fragmentation of oil droplets with time, which occurred after long hours of mixing, leading to the formation of massive OPA clusters. Various lines of inquiry strongly suggested that protruding particles get torn from oil droplets and carry oil with them, causing the torn particles to be amphiphillic so that they contribute to the formation of massive OPAs of smaller oil droplets (<~5-10 µm). Low particle concentration resulted in large, irregularly shaped oil blobs over time, the deformation of which without fragmentation could be due to partial coverage of the oil droplet surface by particles. The findings herein revealed a new pathway for the fate of oil in environments containing nonnegligible sediment concentrations. [ABSTRACT FROM AUTHOR]

Deepwater hydrocarbon releases experience complex chemical and physical processes. To assess simplifications of these processes on model predictions, we present a sensitivity analysis using simulations for the Deepwater Horizon oil spill. We compare the buoyant multiphase plume metrics (trap height, rise time etc), the hydrocarbon mass flowrates at the near-field plume termination and their mass fractions dissolved in the water column and reaching the water surface. The baseline simulation utilizes a 19-component hydrocarbon model, live-fluid state equations, hydrate dynamics, and heat and mass transfer. Other simulations turn-off each of these processes, with the simplest one using inert oil and methane gas. Plume metrics are the least sensitive to the modeled processes and can be matched by adjusting the release buoyancy flux. The mass flowrate metrics are more sensitive. Both liquid- and gas-phase mass transfer should be modeled for accurate tracking of soluble components (e.g. C 1 − C 7 hydrocarbons) in the environment. • Sensitivity analysis simulations for the Deepwater Horizon oil spill sub sea plume • Integral multiphase plume model for subsea oil and gas blowouts • Simulations for subsea live-fluid releases • Chemical and physical processes associated with bubbles and droplets [ABSTRACT FROM AUTHOR]

We report a field study and numerical modeling of multicomponent flow in a tidal gravel beach in Knight Island, Prince William Sound, Alaska, where oil from the 1989 Exxon Valdez oil spill persisted. Field measurements of water table, salinity, and tracer (lithium) concentration were obtained for around a week during the summer of 2008. The numerical model MARUN was used to simulate the field observations. On the basis of field experiments and numerical simulations, the beach was identified to have a two-layered hydraulic structure: a high-permeability surface layer underlain by a low-permeability lower layer. The hydraulic conductivity was found to be 5 × 10−2 m s−1 for the surface layer and 7 × 10−6 m s−1 for the lower layer. The simulations reproduced the observed water table, salinity, and lithium concentrations accurately. The small flow entering the beach from the land side resulted in a beach water table dropping below the interface of the two layers. This seems to be the major reason for the presence of oil in the lower layer. The exchange flow between the beach and the sea due to tidal influence was ∼2.12 m3 d−1 m−1. The patterns of inflow and outflow rates showed that the maximum seawater-groundwater exchange occurred in the middle to high intertidal zone, which explains the persistence of oil in the lower intertidal zone. To explore bioremediation of the beach with nutrient amendment, a numerical simulation of nutrient application on the beach surface was conducted, where the applied nutrient concentration was 5,000 mg L−1. The results showed that the nutrient concentration remaining in oiled areas after a week was larger than 50 mg L−1, which is larger than that needed for maximum microbial growth (2-10 mg L−1). This implies that the bioremediation via nutrient application on the beach surface could be adopted if nutrients were the only limiting factor. [ABSTRACT FROM AUTHOR]

Numerous laboratory test systems have been developed for the comparison of efficacy between various chemical oil dispersant formulations. However, for the assessment of chemical dispersant effectiveness under realistic sea state, test protocols are required to produce hydrodynamic conditions close to the mixing, transport, and dilution effects found in the natural environment. To this end, we have designed and constructed an experimental wave tank system capable of generating waves of different energy levels, ranging from regular nonbreaking waves to plunging breakers. The hydrodynamics of these wave conditions were characterized using an autocorrelation function method applied to in situ velocity measurements. We report here an investigation of the effectiveness of two chemical dispersants (Corexit 9500 and SPC 1000) on two crude oils (weathered MESA and fresh ANS) under three different wave conditions in the wave tank operated in batch mode. Corexit 9500 dispersed approximately 75% of the weathered MESA and more than 90% of the fresh ANS crude, and SPC 1000 dispersed about 53 and 64%, respectively. Under control conditions (absence of chemical dispersant), only 10 to 20% of the crude oils were dispersed. Quantitative relationships were established between dispersant effectiveness and energy dissipation rate under the different simulated wave conditions. These relationships are essential for the development of accurate predictive models on dispersant effectiveness and operational guidelines for dispersant use. [ABSTRACT FROM AUTHOR]

• Multiphase large eddy simulation of an oil jet in crossflow was conducted. • Oil trajectory and dilution rate were compared to experiments and integral model. • Multiphase model was modified to include the transport term due to the rise velocity of oil droplets. • Jet and crossflow interference created small-sized eddies near the upper edge of the plume. • Counter rotating vortex pair is likely to enhance the mixing of chemicals and droplets within the plume. Experimental results were presented for the release of diesel oil from a one-inch (2.5 cm) vertical pipe in a crossflow at 0.27 m/s. The ratio of jet velocity to crossflow speed was 5.0 and the Reynolds number based on jet velocity and pipe diameter was 7.1 × 10 3. In the experiments, the plume shape was photographed, and the oil droplets were measured at two vertical locations on the center axis of the plume. Acoustic Doppler velocimetry (ADV) data was also obtained and compared to numerical predictions. The plume was simulated using large eddy simulation (LES), and the mixture multiphase model. The impact of the oil buoyancy was captured by adding a transport term to the volume fraction equation. Using the rise velocity based on d 50 (volume-median) droplet size in the lower part of the plume allowed us to capture the lower boundary of the plume, but the estimated upper boundary of the plume penetrated less into the crossflow as compared to the experimental findings. However, using the rise velocity of the d 50 at the upper part of the plume allowed one to estimate the upper boundary of the plume. As the droplets are too small to be resolved by the LES, we could not use a systematic approach to allow the multiphase plume to spread to mimic the observations. Based on the simulation results, the interaction between the jet and crossflow yielded small-sized flow structures near the upper boundary of the plume. The wake vortices initiated from the leeward side of the plume showed an alternating vorticity pattern in the wake. The shear layer vortices were induced by Kevin-Helmholtz instabilities mostly on the windward side of the plume. The formation of counter rotating vortex pair (CVP) altered greatly the hydrodynamics of the jet from that of a vertical jet to manifest flow reversals in all directions. The formation of CVP is likely to enhance the mixing of chemicals and droplets within the plume. [ABSTRACT FROM AUTHOR]

We conducted a large scale experiment of underwater oil release of 6.3 L/s through a 25.4 mm (one inch) horizontal pipe. Detailed measurements of plume trajectory, velocity, oil droplet size distribution, and oil holdup were obtained. The obtained experimental data were used for the validation of the models JETLAG and VDROP-J. Key findings include: (1) formation of two plumes, one due to momentum and subsequently plume buoyancy, and another due mostly to the buoyancy of individual oil droplets that separate upward from the first plume; (2) modeling results indicated that the traditional miscible plume models matched the momentum and buoyancy plume, but were not able to simulate the upward motion plume induced by individual oil droplets; (3) high resolution images in the jet primary breakup region showed the formation of ligaments and drops in a process known as “primary breakup”. These threads re-entered the plume to re-break in a process known as “secondary breakup”; (4) the plume velocity was highly heterogeneous with regions of high velocity surrounded by stagnant regions for various durations. The results from this study revealed that the primary breakup is a key factor for quantifying the droplet size distribution which plays a crucial role in determining the ultimate fate and transport of the released oil in the marine environment. The observed spatial heterogeneity in the oil plume implies that the effectiveness of applied dispersants may vary greatly when applying directly in the discharged oil flow. [ABSTRACT FROM AUTHOR]

In situ burning (ISB) hasn't been widely used for offshore oil spill response for various reasons. We present a feasibility study for a new ISB method – the Burning Tongue (BT) concept. We conducted scaled experiments in the Ohmsett wave tank to demonstrate its feasibility. We produced a 35-m long "tongue" of burnable oil (average oil thickness 4.2 mm – above the thickness needed for ISB) by towing a conventional boom (with a 12″ (0.3 m) deep skirt) partially filled with crude oil and then released the oil through a 6″ (0.15 m) wide opening at the apex. We found that the boom movement produced a convergence zone just downstream that kept released oil thick and also pulled oil that entrained under the boom skirt into the thick "tongue" of oil. CFD modeling was performed to explain the flow hydrodynamics and the formation of the convergence zone, which indicates the phenomenon is universal. We used small harbor boom only partially filled with oil for this study and believe that a full-scale marine boom filled with oil would achieve an even thicker "burning tongue." The BT concept could make ISB more widely used for oil spill response in offshore areas. [Display omitted] • A new ISB concept for offshore application – the Burning Tongue is introduced. • Scaled experiments in a large wave tank successfully demonstrated its feasibility. • The produced 35-m long, 4.2 mm thick oil tongue was well above burning requirements. • A convergence zone was formed downstream of the boom to keep the oil tongue thick. • CFD modeling explained the flow hydrodynamics. [ABSTRACT FROM AUTHOR]

• Experiments and large eddy simulations (LES) of oil jet with different orifice types. • The size of shed droplets in the shear layer increased in the jet direction. • The characteristic size of shed droplets (d 50) was up to 40% larger in the shear layer with pipe orifice. • The energy dissipation rate was higher, and its peak values were found closer to the jet centerline with pipe orifice. • The Reynolds shear stress was found significantly larger with nozzle orifice in the near field of the jet. Experiments were performed to understand the impact of the orifice on droplet size in the shear breakup region. Oil jet was released vertically from two orifice types: a pipe and a converging nozzle. The roll-up vortices were observed clearly near the edge of the jet with nozzle orifice while elongated oil ligaments in the jet direction were mostly observed near the edge of the jet with pipe orifice. The size of the droplets shed from the near field shear layer increased along the jet direction for both orifice types. At different distances from the orifice, the characteristic shed droplet size (d 50) was up to 40% larger with pipe orifice. Multiphase, large-eddy simulations (LES) with two orifice types were conducted to interpret the droplet size distribution (DSD) observed in the experiments. A thicker boundary layer that was initially formed inside the pipe dominated the near field of the jet with the pipe. The turbulent kinetic energy dissipation rate (ε) was higher with pipe orifice and the peak values of ε were found closer to the jet centerline with the pipe where oil holdup is larger. The viscous shear stress with the nozzle was higher than that of the pipe orifice within the initial two diameters from the orifice and slightly lower or higher at the following distances studied. The Reynolds shear stress was significantly larger with the nozzle at different distances from the orifice. The tangential vorticity within one diameter from the orifice was also dramatically higher with the nozzle. The key parameter in the shed droplet size of a liquid jet in liquid was found to be the shear layer thickness at the orifice, similar to prior works of a liquid jet in gas. A thicker shear layer at the pipe orifice induced a larger droplet size. The increase in the instabilities and shear layer thickness in the jet direction increased the droplet size in the jet direction. [ABSTRACT FROM AUTHOR]