SEMINAR: Particle capture by cylindrical collectors in aquatic environmental processes

Particle capture, whereby suspended particles contact and adhere to a solid surface (a ‘collector’), is an important mechanism for a range processes. The filtering of aerosols and the analysis of particle deposition over heat exchanger surfaces are two examples of mayor importance for industry. In aquatic environmental systems, 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). But flow conditions may well be above Re=1 (the limit of the existing theory), and even above the onset of vortex shedding (i.e. Re > 47 for cylindrical collectors of circular section). We have used two- and three-dimensional direct numerical simulations (DNS) to accurately quantify the rate of capture of low-inertiaparticles from Re->0 up to Re =1000. By doing so, we were able to extend the applicability of the existing low-Re analytical expressions for estimating the fluid velocity around a circular cylinder at higher Re; and to describe thespatial variability of the self-induced oscillatory conditions near the leading face of the cylinder when vortex shedding is present, and their influence on particle trajectories and capture efficiency. Our results fill a gap between theory and experiment by providing, for the first time, predictive capability for particle capture by aquatic collectors in wide (and relevant) Reynolds number, particle size and particle density ranges