Computations of Buoyancy Driven Motion of a Single Droplet in Another Immiscible Liquid

Buoyancy driven motion of a single droplet in another quiescent fluid was simulated by a Front-Tracking method. The rising velocity and the projected area of the droplet were obtained in spherical, ellipsoidal, and wobbling regimes. Form and skin drag forces were calculated by integrating pressure distribution and velocity profiles along the interface of the droplet. Drag coefficient was obtained from those values when the rising velocity reached the terminal velocity. The scaling for drag of a liquid droplet was compared with the theoretical model. When the viscosity of the droplets was lower than that of the surrounding fluid, the drag coefficients can be predicted by the model for the limiting case of gas bubbles. When the viscosity of the droplets was larger than that of the surrounding fluid, on the other hand, the drag coefficients can be predicted by the model when solid particles are assumed.