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Settling and Rising Hydrodynamics of Microplastic Contaminants: A Numerical Investigation

Author(s): Zihe Zhao; Shooka Karimpour

Linked Author(s): Zihe Zhao, Shooka Karimpour

Keywords: Microplastics; Settling and rising; Environmental hydrodynamics; Computational fluid dynamics; ANSYS Fluent

Abstract: With ever-growing plastic production rates, the pollution of microplastics (MPs) has become a major environmental problem in the 21st century. MPs, which are typically defined as plastic particles having diameters smaller than 5 mm, can be transported far into various aquatic environments. Due to MPs’ widespread pollution in aquatic environments, it is crucial to investigate their hydrodynamics. MPs, apart from having a wide range of sizes and densities, are found with highly variable shapes. This makes MPs particularly difficult to characterize. So far, numerical investigation that sufficiently accounts for MPs’ complex shapes does not exist. To accurately predict the fate and transport history of MPs in natural aquatic environments, a model that could simulate the settling and rising hydrodynamics of intricately shaped microplastics is particularly useful. In the present study, a Finite Volume-based three-dimensional numerical model is used to investigate the trajectory and settling or rising patterns of MP particles of wide variety of shapes and densities. To accurately represent the MP particle, a numerical cavity with a predefined shape, density, and moment of inertia is introduced in the model. This cavity is coupled with the six degree-of-freedom (6DOF) solver in ANSYS Fluent so that the cavity moves according to its gravitational force and the drag force it receives at its boundary. Our initial results suggest that the present model is capable of simulating the dynamics of micro-sized plastics in a quasi-static fluid. Preliminary results with MP particles of regular shapes are shown to be consistent with previous experimental data available for both MPs and sediment particles. Irregularly shaped MP fibers and sheets are also tested with the model. Results from the present model will be used to parameterize MP particles with irregular shapes, enabling the prediction of MPs’ transport history through large-scale models.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221436

Year: 2022

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