Droplet arrival pattern, clustering and settling velocity in a polydisperse droplet field

Understanding the onset of clustering is an essential consideration in many engineering and natural systems. High operating costs and sophisticated methods associated with the existing spatial measurement techniques in clustering analysis call upon the use of low-dimensional measurements. In this experimental study, we study the 1D temporal droplet diameter data in a polydisperse droplet field with a background turbulence, to directly demonstrate a viable relationship between inertial clustering and the droplet arrival pattern. Upon the onset of clustering, a substantial increase is observed in the occurrence of ordinal patterns containing monotonically increasing sub-patterns, where smaller droplets are followed by bigger droplets, and a clear bifurcation in the occurrence of these patterns with downstream location is observed. These trends are understood in terms of droplet settling velocity. The mean flow dominated background turbulence enhances the settling velocity of clustered droplets, which induces a size–velocity correlation of the droplets and, as a result, increases the occurrence of ordinal patterns containing monotonically increasing sub-patterns. This study shows the potential of using low-dimensional measurements for the qualitative understanding of complex flows in different natural and engineering systems.