Forced Liquid Droplet Oscillations

The behavior of liquid droplets in the presence of an acoustic field is one of the fundamental problems in fluid mechanics. There are a variety of applications in which droplets are excited by acoustic energy, such as meteorological physics, containerless processing, and atomization. The primary motivation for this research is to study the behavior of acoustically influenced droplets as they pertain to atomization applications.

Droplet oscillations in the absence of external excitation will ultimately dissipate, and the drop will return to its equilibrium state. However, a strong acoustic field may be present, such is the case in airborne combustors and acoustic levitators. In such a situation, the droplet will experience forced oscillations. This oscillatory behavior of drops may greatly affect the process of atomization. For this reason, there are researchers who have studied this phenomenon analytically and experimentally.

The focus of this work is to examine the nonlinear interaction between a droplet and an acoustic disturbance in surrounding gas flow. The liquid and gas domains were assumed to be inviscid and incompressible. The interaction between the droplet and the perturbation is characterized by the ratio of gas to liquid density, Weber number, and the frequency ratio. The Weber number (We) is a ratio of inertial and liquid surface tension forces. In this problem, changes in the magnitude of the acoustic disturbance are introduced through the Weber number. The ratio of the acoustic frequency of the gas and the linear natural frequency of the second mode for a fluid drop is defined as the frequency ratio.