Time-resolved measurements of clustered particles in channel flow turbulence

Small heavy particles in turbulent flows preferentially concentrate forming clusters, regions of high local concentration. The temporal persistence of these clusters and the dynamics of clustered and non-clustered particles are experimentally investigated in the core region of a vertical turbulent channel flow for different particle to flow time scales ratios (St_η) by independently varying particle and flow parameters. The Stokes number is varied in the range 0.6 to 54 while keeping particle sizes smaller than the dissipative scales in all cases, and particle volume loadings at about 4.8x10^-5 to minimize global flow modification by particles. Synchronous high-speed imaging from two cameras with different but overlapping fields of view is used to measure particle trajectories and velocity statistics, and cluster dynamics. We focus on the kinematics of clustered particles conditioned on local concentration and explore their correlation with cluster size and lifetime. This research aims to develop phenomenological models for particle cluster evolution and to advance our understanding of particle preferential concentration in turbulence.