Abstract
Drop motion on a dry solid substrate is determined by the lateral adhesion force associated with the contact angle hysteresis and by any applied external forces. In this experimental and computational study the lateral adhesion force is measured directly, through dragging of a drop along a surface by a cantilever. These force measurements are compared with the estimated value of the aerodynamic force needed to displace a wall-bound drop in a channel flow. The scaled lateral adhesion and aerodynamic forces are functions of the capillary number. Their values agree for capillary numbers higher than . For smaller capillary numbers, , the value of the required aerodynamic force can be smaller than the lateral adhesion force. This unexpected result is explained by the complex three-dimensional periodic motion of the drop, similar to a shuffling gait. During the shuffling gait propagation, at any instant only a part of the drop contact line propagates, which requires a smaller force to displace the drop. Alternating motion of different parts of the contact line forms a continuous shuffling gait propagation. As soon as the aerodynamic force exceeds a threshold value the drop slides nearly steadily.
5 More- Received 29 January 2020
- Accepted 19 August 2020
DOI:https://doi.org/10.1103/PhysRevFluids.5.094006
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