Breakup of individual colloidal aggregates in turbulent flow investigated by 3D particle tracking velocimetry

Aggregates grown in mild shear flow are released, one at a time, into homogeneous isotropic turbulence where their breakup is recorded by three-dimensional particle tracking velocimetry (3D-PTV). The aggregates have an open structure with fractal dimension around 2.2, and their size varies from 0.9 to 3.1 mm which is large compared to the Kolmogorov length scale η = 0.15 mm. 3D-PTV allows for the simultaneous measurement of aggregate trajectories and the full velocity gradient tensor along their pathlines which enables us to access the Lagrangian stress history of individual breakup events. The analysis suggests that aggregates are mostly broken due to accumulation of drag stress over a time interval of order Kolmogorov time scale, O(τη). This finding is explained by the fact that the aggregates are large, which gives their motion inertia and which increases the time for stress propagation inside the aggregate.