Particle capture in aquatic systems

[Truncated abstract] Particle capture, whereby suspended particles contact and adhere to a solid surface (a ‘collector’), is an important mechanism for a range of processes. This thesis focuses on particle capture in aquatic environmental systems, where the rate of particle capture determines the efficiencies of processes such as seagrass pollination, suspension feeding by corals, larval settlement and ‘filtering’ by wetland vegetation. Particle-laden flows in aquatic systems are typically characterized by low-inertia particles and low collector Reynolds numbers (Re). Consequently, direct interception, the mechanism of capture of zero-inertia particles (i.e. particles that exactly follow fluid pathlines) is important in aquatic systems. However, the Reynolds number (Re) of the flow may well be above 1 (the limit of existing analytical theory), and even above the onset of vortex shedding (i.e. Re > 47 for cylindrical collectors of circular section). I use two and three-dimensional direct numerical simulations (DNS) to accurately quantify capture efficiency by direct interception for steady flow (i.e. Re ≤47) and also for the unsteady flow conditions in which vortex shedding is present (in the range 47 < Re ≤ 1000).