Clustering of inertial particles in sheared flows

The formation of clusters is one of the most prominent phenomena associated with the transport of inertial particles in turbulent flows. This mechanism plays a key role in a variety of environmental and industrial contexts, including sediment transport in rivers, microplastics in oceans, and pollutant dispersion in the atmosphere, among others. While most real-world scenarios involve inhomogeneous turbulent flows, clustering in such systems has rarely been explored experimentally.

We present wind tunnel experiments in which micrometric water droplets are uniformly seeded into the flow. By employing different grids to generate either homogeneous or inhomogeneous turbulence, we test background flows that are nearly homogeneous and isotropic, as well as flows with imposed uniform shear. Various experimental conditions are explored, including different distances from the grids and freestream velocities. A Voronoi analysis is used to quantify differences in clustering behavior between the two turbulence regimes. In addition, particle image velocimetry, performed using the seeded inertial droplets, enables us to investigate the rotation of clusters under shear conditions.