Entrapment of air at 45° oblique collision of a water drop with a smooth solid surface at room temperature

This paper treats the oblique impact of a water drop onto a smooth optical glass surface at room temperature. The impact angle between the incoming drop and the surface is 45°. The preimpact diameter of spherical drops is 2.55 mm. The time evolution of the water/solid direct contact area is observed from the reverse side of the impact surface by a flash-photographic technique. It is found that the drop directly contacts the solid surface in a ring shape, and some air is entrapped between the bottom of the drop and the solid surface. Thereafter, a bubble is formed at the impact point. For the case of impact velocity at 1.31 m/s, a fingering pattern is developed from within a ring-shaped wet area, then satellite bubbles in a ring are formed around the bubble at the impact point. No satellite bubble is observed for the case of a higher impact velocity (=2.11 m/s).