Although the image may evoke the impression of a clear night sky, it captures an instantaneous snapshot revealing micron-sized glass particles (depicted as white dots) being transported through a channel by fully-developed turbulent airflow. Despite being initially seeded uniformly, the particles evidently do not distribute homogeneously in space. Instead, they preferentially accumulate in certain areas, forming distinct clusters (regions of high particle-density) and void regions. Interestingly, this preferential accumulation occurs spontaneously due to complex multiscale interactions between the inertial (heavier than air) particles and turbulent eddies of the underlying flow. While the exact mechanism of particle clustering is not fully understood to date, it significantly influences various natural and industrial processes, including cloud formation, atmospheric pollutant dispersion, sediment transport, fluidized-bed combustion, etc. Most strikingly, such particle clustering follows a self-similar (scale-invariant) distribution. This implies that, with appropriate non-dimensionalization, the cluster statistics obtained in a small laboratory-scale channel (~50 mm) would accurately represent atmospheric cloud formation phenomena (~several kilometers). Furthermore, recognizing that the formation and spatial distribution of celestial objects are influenced by interstellar turbulence, it’s no wonder that the image resembles the view of a night-sky!
