Researchers model high-speed drop impact on thin films

The seemingly simple phenomenon of a liquid drop striking a surface, called drop impingement, requires rather complex modeling. Drop size, impact velocity, and surface tension must be factored into the model to predict behavior of the drop upon impact.

Drop impingement has many applications including spray cooling and inkjet printing. The same principles apply to droplets of supercooled liquid water that accumulate on the surface of an aircraft, which can be hazardous to flight. Two University of Louisville engineers, who focus on this type of aircraft icing, numerically investigated high-speed drop impact on thin liquid films. They report their findings in Physics of Fluids.

The numerical simulation code used by Yisen Guo and Yongsheng Lian solves the Navier-Stokes equations, which describe fluid motion. The moment-of-fluid (MOF) method was used to construct the interface between the drop and liquid film.

Guo and Lian validated their code against experimental data from water drop impact onto water film. They found good agreement for low-speed impact on thick liquid film, and both low- and high-speed impact on thin liquid film. The numerical simulation also matched theoretical predictions of crown radius change.

For the high-speed model, the authors found that a higher tangential velocity leads to lower lamellar height and radius on the side behind the advancing drop. Also, a thinner liquid film led to a thinner expanding crown and earlier crown breakup. Lastly, Guo and Lian observed that lower film density causes an earlier splash to occur, but the drop then later tends to move beneath the liquid film.

Next, Guo and Lian plan to simulate the icing process of supercooled drop impact on a solid surface.

Source: “High-speed oblique drop impact on thin liquid films,” by Yisen Guo and Yongsheng Lian, Physics of Fluids (2017). The article can be accessed at https://doi.org/10.1063/1.4996588 .