Unraveling the persistence and dynamics of high-concentrated regions of inertial particles in turbulent flows

Inertial particles in turbulent flows preferentially concentrate forming regions of high particle concentrations. The persistence of these high-concentrated regions over time and the associated dynamical behavior of the particles confined in these regions are investigated in this study. Time-resolved data of sub-Kolmogorov solid particles is collected at the central plane of a vertical channel for varying Reynolds number and particle volume fraction. Local regions of high concentration are identified based on the particle number density surrounding a particle in its neighborhood. To quantify the persistence of these high-concentrated regions, temporal autocorrelation of local concentration fluctuations along the particle-tracks is studied conditioning on the initial local concentration. The timescale for which the autocorrelation function remains above 0.5, is defined as the coherence time of the local concentrated region. The variation of the coherence time with the initial local concentration is reported. The effect of Stokes number on the coherence time for a particular value of initial local concentration is also examined. The kinematics of the particles confined in these concentrated regions are analyzed to gain insights into the influence of collective inertia of high-concentrated regions on particle behavior.