Droplet impact on a dry surface: triggering the splash with a small obstacle

Droplet impact on a dry solid surface is investigated experimentally. A small obstacle made by layers of adhesive tape is located on the solid surface at some distance from the impact centre. The splashing of the drop starts at the tape, as a sheet of liquid shoots upwards. Angle, speed and dynamics of this liquid sheet are investigated as a function of the distance from the impact centre to the obstacle and its height. Reynolds and Weber numbers are kept constant. Volume-of-fluid simulations reproduce the experiments qualitatively. Measured sheet angles are compared with the predictions of a simple theory.