Slightly curved surfaces are capable of triggering the early transition of impacting behavior from spreading to splashing. In this study, the ejection dynamics of droplets impacting on superheated concave surfaces are experimentally and theoretically investigated. The changed ejection dynamics, including the delayed ejection but enhanced ejection velocity, are considered to be causes for the changed impacting behavior and the consequences from the change in the ejection mechanism on a concave surface. The curvature radius of the concave shape surface is found to significantly affect the ejection time and ejection velocity of the lamella. We propose a simplified model by ascribing the reacting force from the curved surface as the key factor in the changed ejection dynamics and predict the delayed ejection that matches reasonably with the measured values, suggesting its potential in predicting the spreading–splashing transition for impacting droplets on non-flat surfaces.
Hu et al. (Sun,) studied this question.