Scale-dependent particle clustering in transitional wake flow

Dispersion and mixing of inertial point particles in the unsteady three-dimensional wake a circular cylinder at $Re=200$ are investigated via one-way coupled simulations. The presence streamwise-oriented vortical braids originating from mode A instability transition regime has profound impact on particle dynamics preferential concentration near wake. Particles trapped between Kármán rollers streamwise form an inner layer densely concentrated particles, while discrete clumps otherwise thin ribbon-like clusters two consecutive another manifestation braids. effect inertia size voids ascribed to centrifugal ejection is examined by volume-averaged Voronoï analysis. distinct dependence Stokes number ( $Sk$ ) seen cluster scale, whereas void scale exhibits self-similarity. New physics-based threshold values distinctly different probability-distribution-based scale. Increasing found suppress acceleration more than deceleration. velocity further suppressed effects vary non-monotonically with strongest $Sk=1$ when most tend reside high-strain/low-vorticity regions.