Influence of a local change of depth on the behavior of walking oil drops
Bouncing liquid silicone oil drops on a vertically oscillating bath of the same liquid were studied experimentally. The different bouncing regimes previously described in the literature were observed, with transitions depending mainly on the droplet size and the forcing acceleration of the oil bath. In a particular range of forcing amplitudes, just below the Faraday instability threshold where standing waves appear on the free surface, walking drops traveling at a constant velocity over the surface were observed, consistent with previous studies. The influence of a local change of depth on this walking behavior was studied by submerging an obstacle in the oil bath. Notably different to the study of Eddi et al. (2009) , the depth change was such that walking was still observed over the obstacle. Previously unobserved drop trajectories, including trapping of a walking drop over the obstacle, crossing for non-normal drop approach to the obstacle, and reflection from the rear face of the obstacle were observed and explained in light of recent results and models in the literature.
© 2014 Elsevier Inc. Received 21 August 2013; Received in revised form 24 December 2013; Accepted 26 December 2013; Available online 11 January 2014. Support from a National Science Foundation Graduate Fellowship (S.S.) and the Graduate Aerospace Laboratories at the California Institute of Technology is gratefully acknowledged.