Transport and Capture of Neutrally Buoyant Particles in Streams: Investigating the Effect of Obstacle Configuration

The transport of particles in water is a mechanism observed from various scientific and engineering problems such as the removal of polluted particles, optimal sampling of organic matter, transport of fish eggs and plant seeds. Thus, it is necessary to understand the transport mechanism of particulate matter in water thoroughly to manage the aquatic ecosystem effectively. In this study, we analyze the transport of neutrally buoyant particles in a laboratory setting when obstacles are fixed at the bottom with different configurations, focusing on the spacing between neighboring obstacles at different flow depths and velocities. The spatial and temporal analysis of two-dimensional velocity fields yield valuable information on flow-structure-particle interactions and their response to changing hydrodynamic conditions. We conducted experiments on a closed-loop racetrack flume, using Particle Tracking Velocimetry (PTV) to identify plastic transport and their preferred locations relative to the obstruction, and Particle Image Velocimetry (PIV) to identify specific mean and turbulent conditions that determine particle retention or redirection. Based on the result, we computed two parameters, the dimensionless capture ratio and retention time of particles to quantify the effect of submerged obstructions on the transport of particles. Spectrum analysis and quadrant analysis are applied to show that large scale eddies appear at the threshold gap length and lead to high concentration of particles inside the gap between adjacent obstacles, creating a favorable condition to capture particles effectively.