Splashing generation by water jet impinging on a horizontal plate

The report of COVID-19 virus in municipal wastewater raises the question of whether viruses can become airborne during wastewater transport in sewer systems. The present work experimentally investigates a water jet impinging vertically onto a horizontal plate and the behaviours of the generated tiny droplets. Depending on whether the jet breaks into primary drops before the impingement, three regimes can be defined: non-splashing, jet-splashing and drop-splashing regimes. The splashing ratio, i.e., the portion of jet flow rate becoming splashing droplets, ranges from 1% to 70% in the drop-splashing regime, while it remains less than 2% in the jet-splashing regime. For the splashing droplets, their size and velocity distributions follow log-normal laws. Their diameters are mainly in the range from 0 to 0.3 of the impact jet or drop diameter with the median less than 0.1. Their velocities mostly range from 0 to 3.0 times of the impact velocity with the median around 1.0. The medians of both the dimensionless diameter and velocity of splashing droplets decrease with the impact Weber number. The ejection angles of splashing droplets obey a bell-shaped distribution with the maximum around 70° and the median ranging from 16° to 30°.