Study of morphological characteristics and gravitational potential energy of crater formed by droplet impact

The processes of single droplets with different diameters and different speeds impacting on the liquid pool with different depths were captured using a high-speed camera. The morphological characteristics of the craters were analyzed. For the deep liquid pools, when the volume of the crater reaches the maximum, its shape is approximately a hemi-sphere. However, for the shallow liquid pools, due to the restriction of the pool bottom, the crater cannot fully develop. Thus, when its volume reaches the maximum, the shape of the crater looks like a hemi-sphere with the bottom being cut-off. For the deep liquid pools, the liquid jet is thick and short, and the number of the secondary liquid droplets is less. For the shallow liquid pools, the liquid jet is fine and high, and the number of the secondary liquid droplets is more. The dimensionless maximum horizontal length and the dimensionless maximum depth of the crater increase with the increase of the Weber number. The larger the diameter of the droplet is, the smaller the dimensionless maximum horizontal length and the dimensionless maximum depth are. For the deep pools, both the dimensionless maximum horizontal length and dimensionless depth increase with the decrease of the pool depth. However, when the pool depth is decreased to a certain value, the dimensionless maximum horizontal length and dimensionless maximum depth decrease significantly. The existing gravitational potential energy model of the crater was extended, and the law of the gravitational potential energy of the crater was analyzed. The gravitational potential energy of the crater increases with the increase of the initial kinetic energy of the droplet. For the deep liquid pools, the gravitational potential energy of the crater increases as the depth of the crater decreases. For the shallow liquid pools, the ratio of the gravitational potential energy to the initial kinetic energy of the droplet is lower.