Experimental Splash Studies of Monodisperse Sprays Impacting Variously Shaped Surfaces

Abstract

Despite numerous studies of the drop impact phenomena, studies of the fundamental mechanisms of how the splash corona and subsequent necking yield splashed droplets, not to mention characteristics of these splashed droplets, remain a subject of great interest. Here, we consider a simple question: After impact, what are the characteristics of splashed droplets? Spatial variations in the fraction of splashed liquid, Sauter mean diameter, and drop-size distribution for water and diesel impacting onto variously shaped rods are reported. Liquid drops of nearly uniform size are continuously injected onto a 2-mm-diameter aluminum cylindrical rod at velocities of up to 17 m/s. The impact face of the rod is flat with angles from θ = 0 to 60° or it has a concave, convex, or conical shape. The experimental results indicate that diesel breaks up more easily than water due to its low surface tension. However, due to increased energy loss through viscous dissipation during drop collapse and spreading, dispersion of diesel drops upon and after impact is less energetic than that of water since diesel droplets do not travel as fast or as far as water droplets. During corona formation, stretching and necking of diesel drops before their snap-off are particularly evident due to diesel's high viscosity. Size distribution of splashed diesel droplets is more uniform than that of water near the impact region and water is more uniform further away.