Experimental investigation of droplet descent dynamics and dry surface impacts in a variable ambient pressure environment.

In this study, the effects of ambient pressure on the descent and subsequent impact of a Newtonian fluid droplet on a dry smooth surface are investigated using high-speed photography. Video acquisition of droplet decent and impact was performed at 20,000 frames per second in a transparent vertical chamber pressurized up to 4 atm.



Previous studies have shown that ambient pressure can affect splash dynamics on a dry surface due to changes in the entrapment of ambient gas between the droplet and the surface. The present study considers the impact dynamics in conjunction with the effect of the change in atmospheric pressure on the shape of the descending droplet.



The experiments show that under an ambient pressure of 4 atm, average droplet shape became oblate, and the fluctuations of the aspect ratio of the droplet increased during its descent, compared to standard atmospheric pressure conditions, where the droplet shape was nominally spherical, and the shape oscillations were smaller. During the subsequent impacts of the droplets on a dry smooth surface at the velocity of approximately3 m/s, small secondary droplets of ~50 µm in diameter were ejected in the higher ambient pressure scenario, while no secondary droplets were observed under standard atmospheric pressure conditions.