Consideration of Airflow Aided Single High-Speed Droplet Generation Method

Abstract

The water hammer pressure at the high-speed droplet impact has not yet been elucidated, and a reproducible droplet generator is needed to investigate it. We developed a single droplet generation device using airflow with an abrupt contraction pipe. We obtained higher velocity droplets than the smooth convergence tube of the early study. To clarify the reasons, we investigated the details of the droplet acceleration using the fluid analysis software OpenFOAM, especially focusing on the pressure gradient force in the abrupt contraction pipe. Comparing the experimental and simulation results, we found that the pressure gradient force has a small contribution to the droplet acceleration and the drag force is dominant for the motion. After examining various shapes, such as a combination of a smooth convergence with a straight pipe, we found that applying as large a drag force as possible at the beginning of acceleration leads to efficient acceleration.