Numerical analysis and experimental validation of the interaction of droplet oscillation and gas flow separation for two adhering droplets in a channel flow

Abstract Droplets and their movement on solid walls can be observed in many technical applications. The droplets can be moved by external forces, e.g. aerodynamic or vibrational forces. If the velocity of the gas flow is higher than a critical one, the gliding motion of the droplet starts. Before the gliding motion, i.e. the droplet is still pinned, an oscillation of the contour can be observed. In this work, the interaction of the droplet oscillation and the surrounding gas flow is studied experimentally and numerically for two droplets with different diameters and in a channel flow which are positioned at various distances in flow direction. It can be shown, that the frequency of the gas flow separation corresponds to the Eigenfrequencies (EFs) of the droplets. For larger distances between droplets, only the second EF of the droplet in the backflow can be detected in the frequency spectra of the gas flow. If the distance is smaller than two droplet diameters, the first and second EF can be measured.