Crown and drop rebound on thin curved liquid films

Abstract

Experimental and theoretical work was conducted to enrich the previous study concerning a single liquid drop impinging on curved liquid films. Two typical outcomes including crown sheet at high impact velocity and drop rebound at low impact velocity were mainly discussed. Different from the traditional crown on a flat film, the crown on curved films has larger upper size but smaller base size. Increasing Weber number produces a positive influence on crown diameter when sphere-drop curvature ratio is higher than 0.303. While this effect is minor for curvature ratio of less than 0.114. By reducing curvature ratio, crown diameter first increases then remains unchanged. An empirical formula was also provided to predict the crown scale. With respect to drop rebound, a physical model was established to assist theoretical derivations. Based on energy conservation, a theoretical formula for predicting the inferior limit of rebound thresholds was obtained to offset deficiency in experiments, which involves Froude number and a deformation factor. In this work, the inferior limit of the critical Weber number is 0.8, applied to drop bouncing off both a curved film and a flat film.