Interfacial deformation between an impacting water drop and a silicone-oil surface.

Abstract Detailed observations have been conducted on the interfacial deformation of a silicone oil surface and a water drop falling on it. Eleven kinds of silicone oils with wide variations of kinematic viscosity, ν T =1–10 5  mm 2 /s, have been tested. The oil surface is disturbed by a water drop with a diameter d L =3.1 mm, which falls freely on it from a height of 100–1000 mm. Special attention has been directed to the maximum depth of the cavity formed on the oil surface D M and to the maximum diameter of the water drop spreading on the oil surface d M . We have categorized the configurations of the oil cavity into seven patterns, and those of the water drop at the oil–water interface into five patterns. The maximum cavity depth D M / d L can be well correlated by a dimensionless group Re TL We TL , where Re TL is Reynolds number based on d L and ν T and We TL is Weber number with the water density and surface tension of oil. The maximum diameter of the impacting water drop d M / d L can be correlated by the Reynolds number with a viscosity of water ( Re L ) and the Ohnesorge number ( Oh ). Moreover, the condition under which the impacting water drop is smashed into pieces has been also examined based on Re L and Oh .