MEASURING FLUID INTERFACES, CORNERS, AND ANGLES FROM HIGH-SPEED DIGITAL IMAGES OF IMPACTING DROPS

Modern high-speed digital cameras enable the investigation of fluid flows with unprecedented resolution in both space and time. A remarkable example is given by the study of drop impact and dynamic wetting phenomena, which occur on time scales of few milliseconds and exhibit features, such as the contact angle, which are often treated as geometric singularities. Whilst a good resolution of the camera sensor and a high-quality optics are obvious prerequisites to obtain accurate measurements, the extraction of quantitative information from digital images always requires some kind of processing algorithm. In particular, the accurate measurement of the position and velocity of fluid interfaces, and that of contact angles, require the identification of image features such as contours, edges, and corners, which represents a nontrivial problem of digital image processing with fundamental applications in machine vision systems. This work illustrates systematic analytical procedures to identify fluid interfaces, corners, and angles in high-speed digital images of fluid flows, with focus on their application to the study of drop impact and dynamic wetting phenomena.