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An experimental Stommel Retention Zone facility with an application to oil droplet dispersion
Summary
This laboratory study designed and tested a novel facility to reproduce Stommel Retention Zone flow patterns associated with Langmuir circulation, which are known to influence subsurface retention of particles such as oil droplets and microplastics. Oil jet injection experiments were conducted in the facility and analyzed using particle image velocimetry and computational fluid dynamics to characterize droplet retention behavior. The results provide foundational data on how buoyant particles accumulate in these ocean circulation features, with implications for oil spill modeling and microplastic transport.
Abstract Stommel Retention Zones (SRZs) associated with wind‐driven Langmuir circulation (LC) facilitate the subsurface retention of particles and thus affect processes such as oil spill dispersion, sediment suspension, oil–particle aggregation, and plankton distribution. Since the effect of SRZs on these processes is difficult to study in the field, we present a novel laboratory facility designed to recreate the counterrotating vortex pair flow pattern associated with small‐scale SRZs of various strengths in two dimensions (2D). We then inject an oil jet into this facility to study buoyant oil droplet retention in these SRZs. 2D particle image velocimetry and hybrid Reynolds‐averaged Navier–Stokes/large eddy simulation are used to characterize the flow. Large‐scale oil droplet trajectories in the SRZs are visualized, and oil droplet statistics in the downwelling region and vortex core are measured using high‐magnification brightfield imaging and a droplet detection algorithm. Values of maximum velocity (7.7–32.2 mm s −1 ), turbulent kinetic energy (10 −6 to 10 −4 m 2 s −2 ), and turbulent kinetic energy dissipation rate (10 −7 to 10 −5 m 2 s −3 ) in the downwelling region of the facility fall within the range of values observed in the field. Flow field strength strongly influences oil droplet trajectories, the shape and size of the SRZ, and oil droplet statistics over time, with stronger flows retaining larger oil droplets in the downwelling region over longer periods of time. Indeed, droplets of almost 400 μ m diameter are observed in the downwelling region after almost 10 min for the strongest flow. The facility may be used to study the behavior of microplastics, sediments, and zooplankton in LC in the future.