Extreme clusters and particle memory in decaying  hydrodynamic turbulence

Particles of different densities are known to show variations in acceleration statistics and preferential concentrations in statistically stationary turbulence. Yet, there is a limited understanding of whether a universal clustering response is possible in decaying isotropic turbulence. We show that decay can drive an increase in the clustering, exceeding even the upper bound of clustering possible in stationary turbulence. Standard deviation of cluster volumes show non-monotonic trends depending on the particle inertia and density ratio, although the mean cluster size does grow in decaying turbulence. We show that the fractal dimension of clusters for particles of wide-ranging densities may be collapsed using a revised effective evolving Stokes built on an intermediate sized eddy.