Numerical simulations of environmentally relevant multiphase flows
File(s)
Author(s)
Abdal, Abdullah M S H
Type
Thesis or dissertation
Abstract
The accumulation of marine debris has become an environmental challenge, threatening marine ecosystems and coastal communities. The abundance of plastic debris in the ocean serves as the motivation for the work carried out in this thesis. The focus of this thesis is on the transport of particles in inhomogeneous fluids, as it is important to gain an understanding of what happens at the particle scale to help combat marine pollution. In the ocean, ambient stratification caused by salinity or temperature gradients can play a crucial role in the transport and fate of microplastics. In this thesis, our in-house solver, BLUE, is used to perform direct numerical simulations of particle transport and interactions in homogeneous and density-stratified fluids.
Firstly, an investigation on the effect of ambient fluid stratification on the vertical transport of particles with different geometries is performed, benchmarking the results against the literature. Furthermore, this thesis considers the rising dynamics of perforated discs in both homogeneous and density-stratified fluids, where the results present the effect of stratification and perforations to suppress the fluttering dynamics otherwise found for impervious discs in homogeneous fluids. A pairwise interaction study of spheroids with varying aspect ratios is also conducted at low Reynolds numbers, drawing comparisons to the behaviour of spheres under similar conditions. Increasing the particle count to a sparse cluster of spheres is then examined to assess how ambient fluid stratification influences the temporal evolution of the cluster variance opposed to its homogeneous counterpart. Lastly, microplastics in the ocean are susceptible to bubble scavenging, in which rising bubbles capture suspended particles by attaching to the air/water interface and carrying them upward. In the last chapter, we consider the interaction between a rising bubble and a settling sphere of a similar size, investigating the role of the dimensionless numbers, which characterise the flow.
Firstly, an investigation on the effect of ambient fluid stratification on the vertical transport of particles with different geometries is performed, benchmarking the results against the literature. Furthermore, this thesis considers the rising dynamics of perforated discs in both homogeneous and density-stratified fluids, where the results present the effect of stratification and perforations to suppress the fluttering dynamics otherwise found for impervious discs in homogeneous fluids. A pairwise interaction study of spheroids with varying aspect ratios is also conducted at low Reynolds numbers, drawing comparisons to the behaviour of spheres under similar conditions. Increasing the particle count to a sparse cluster of spheres is then examined to assess how ambient fluid stratification influences the temporal evolution of the cluster variance opposed to its homogeneous counterpart. Lastly, microplastics in the ocean are susceptible to bubble scavenging, in which rising bubbles capture suspended particles by attaching to the air/water interface and carrying them upward. In the last chapter, we consider the interaction between a rising bubble and a settling sphere of a similar size, investigating the role of the dimensionless numbers, which characterise the flow.
Version
Open Access
Date Issued
2026-03-02
Date Awarded
2026-08-01
Copyright Statement
Attribution-Non Commercial-No Derivatives 4.0 International Licence (CC BY-NC-ND)
Advisor
Matar, Omar K
Publisher Department
Department of Chemical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)