Inhibition of oil plume dilution in Langmuir ocean circulation

Abstract

Oil spills from deep‐water blowouts rise through and interact with the ocean mixed layer and Langmuir turbulence, leading to considerable diversity of oil slick dilution patterns observed on the ocean surface. Certain conditions can drive oil droplet plumes to organize into distinct bands called windrows, inhibiting oil dilution. Observations of blurred or even diffused plumes are also common, but conditions under which these various dilution regimes emerge are not well understood. Here we use large eddy simulations to explain and quantify the dilution patterns and their dependence on relevant physical parameters. Two mechanisms, the downwelling and dilution due to Langmuir cells and the inhibition of dilution due to buoyancy of oil droplets, compete. This competition can be characterized by the ratio of Stokes drift to droplet rise velocity—the drift‐to‐buoyancy parameter, Db. We find that plume appearance and quantitative measures of relative dilution depend mainly on Db.

Large-eddy simulation and parameterization of buoyant plume dynamics in stratified flow

“…Using various types of SGS closures, these LES models were able to capture instantaneous fine-scale flow structures which were missing in RANS models. Very recently, Yang, Chamecki & Meneveau (2014a) and Yang et al (2015) developed a hybrid LES model for simulating hydrocarbon plume dispersion in ocean turbulence. Using their LES model, Yang et al (2014aYang et al ( , 2015 studied the complex dispersion phenomena of oil plumes released into the ocean mixed layer, and investigated the effects of various environmental mixing mechanisms such as shear turbulence, waves and Langmuir circulations.…”

“…In this study, the hybrid LES model developed by Yang et al (2014aYang et al ( , 2015) is adopted and modified to simulate bubble-driven buoyant plumes in vertically stratified ambient fluid. To validate the model and investigate the essential plume characteristics in a controlled environment, the key simulation parameters are chosen to be similar to those of the laboratory measurements of Seol et al (2009).…”

How Do Oil, Gas, and Water Interact Near a Subsea Blowout?

“…Using LES, Yang et al (2014Yang et al ( , 2015 and Chen et al (2016b) studied oil dispersion in ocean Langmuir turbulence, a flow system that combines the aforementioned fine-scale flow phenomena in the OML. Their LES model solved the filtered Craik-Leibovich equations, which comprise a wave-averaged version of the Navier-Stokes equations but differ from the regular Navier-Stokes equations by inclusion of an extra vortex force term that accounts for the cumulative effects of surface waves on the shear turbulence responsible for generating Langmuir circulations.…”

“…Using their LES model, Yang et al (2014Yang et al ( , 2015 studied the complex dispersion of oil plumes in the OML, capturing simultaneously the effects of Langmuir circulation, turbulence, Stokes drift, and oil droplet buoyancy (Figure 4b-d). Their results reveal that instantaneous oil plume patterns as well as the averaged plume transport direction are affected by two competing mechanisms, downward mixing induced by Langmuir turbulence, characterized by the velocity U S , and the droplet rise, given by w r , summarized by the ratio Db = U S /w r .…”

Oil Droplet Transport under Non-Breaking Waves: An Eulerian RANS Approach Combined with a Lagrangian Particle Dispersion Model

“…The "rule of thumb" [5] is that droplets smaller than 100 µm remain below the surface whereas those larger than 100 µm return to the water surface. Waves combined with wind generate Langmuir turbulence characterized by Langmuir cells which also play a significant role in the vertical and horizontal distribution of oil slicks [6].…”