Interface-dominated sliding compound drops.

We investigate compound drops composed of two immiscible nonvolatile partially wetting liquids that slide down an inclined homogeneous smooth solid substrate based on a mesoscopic hydrodynamic two-layer model in full-curvature formulation. First, we briefly investigate the reference case of a liquid drop that stationarily slides on a liquid layer representing an adaptive substrate. Subsequently, we focus on sliding compound drops employing a parameter study to identify qualitative transitions between different drop configurations and time-periodic behavior as well as the underlying bifurcation structure. After analyzing the dependence of drop velocities and dynamic Young and Neumann angles on driving force, also the influence of the ratios of drop volumes and viscosities is briefly considered. An accompanying discussion of the lateral dissipation profile is used to explain the encountered dependence of drop velocity on their configuration. Finally, we consider the time-periodic fusion-overtaking-splitting behavior found outside the existence range of the stationary sliding compound drops.