Water entry of spheres with various contact angles

Abstract

It is well known that the water entry of a sphere causes cavity formation above a critical impact velocity as a function of the solid–liquid contact angle; Duez et al. (Nat. Phys., vol. 3 (3), 2007, pp. 180–183). Using a rough sphere with a contact angle of $120^{\circ }$ , Aristoff & Bush (J. Fluid Mech., vol. 619, 2009, pp. 45–78) showed that there are four different cavity shapes dependent on the Bond and Weber numbers (i.e., quasistatic, shallow, deep and surface). We experimentally alter the Bond number, Weber number and contact angle of smooth spheres and find two key additions to the literature: (1) cavity shape also depends on the contact angle; (2) the absence of a splash crown at low Weber number results in cavity formation below the predicted critical velocity. In addition, we use alternate scales in defining the Bond, Weber and Froude numbers to predict the cavity shapes and scale pinch-off times for various impacting bodies (e.g., spheres, multidroplet streams and jets) on the same plots, merging the often separated studies of solid–liquid and liquid–liquid impact in the literature.