Settling dynamics and interaction of mixed-density particle arrays in quiescent media*

We investigated the settling dynamics of particle arrays in water, with grains organized in a 10 by 10 pattern aligned in a horizontal plane. The experimental setup utilized spherical particles with a dimaeter of 4 mm and two different densities. Experiments were conducted in a 600 mm high tank with a cross-section of 300 mm by 300 mm. The particle array used a one-diameter spacing between adjacent particles, which were released simultaenously into the quiescent fluid medium. Various particle configurations were tested using particles with relative densities of 1.14 and 1.28 compared to water. The settling motions were captured using particle tracking velocimetry with three synchronized cameras, allowing us to determine the motions of the particles through triangulation during their settling to a depth of 40 particle diameters from their initial release position. Our observations revealed distinct dispersion patterns in mixed particle systems compared to homogeneous systems and dyanmics dependent on the relative particle arrangement. Characterization of the induced flow via stereo-particle image velocimetry provides additional insight into particle interactions and their settling behaviour.