Inertial effects on settling of microplastics in turbulent wavy flows

Ziel

Millions of tons of plastic waste have been found in our oceans over the past 10 years, posing ingestion hazards to marine organisms and our food chain. These plastics enter the ocean either as microplastics (< 5 mm in size) or larger plastics which slowly disintegrate into smaller particles before sinking to the ocean bed due to polymer disintegration and biofouling. While past studies primarily focused on floating debris, the settling dynamics of microplastics below waves, which are turbulent in nature, are not well known. Although models exist and this problem has been looked at, due to the challenges in simulating finite-size particles, point-particle assumptions are generally applied in the analytical and numerical modeling of particle-laden flow. This neglects the effects of particle inertia. Moreover, the combined influence of waves and turbulence on particles of various shapes and sizes has never been coupled. This is a major deficiency in the state-of-the-art. Hence, in this work, I will focus on particle inertia, free stream turbulence, and the combined effects of waves, to pinpoint the key parameters that govern the particle motion in wavy turbulent flows. To represent the microplastics, various modeled particles will be fabricated and tested first in a quiescent flow. These particles will then be released into the large-scale water channel facility at NTNU subjected to free stream turbulence and waves. Two series of experiments will be conducted using advanced flow and wave imaging techniques to track the particle, turbulence, and wave motions simultaneously. The results of this work will lead to improved models for simulating the transport of plastic waste and pollutants in rivers and oceanic flows by incorporating the dominant parameters that have previously been neglected. It will also bridge the understanding between both oceanic and turbulence communities on the transport of microplastics.