Regimes of wettability-dependent and wettability-independent bouncing of a drop on a solid surface

Sharma, Praveen K. and Dixit, Harish N (2020) Regimes of wettability-dependent and wettability-independent bouncing of a drop on a solid surface. Journal of Fluid Mechanics, 908. ISSN 0022-1120

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Tiny drops of millimetre size are known to bounce on a solid surface if the surface is superhydrophobic. Recent experiments show that bouncing can occur even on hydrophilic surfaces under conditions where the drop is supported on a thin cushion of gas preventing it from making contact with the surface. We present a detailed insight into this observation by simulating bouncing dynamics of a drop on a flat solid surface using axisymmetric direct numerical simulations. The dynamics of drop motion is governed by three important dimensionless parameters, namely, Reynolds number, Weber number, and capillary number,. We generate a phase diagram in the plane separating the wettability-independent (non-contact bouncing) and wettability-dependent (contact bouncing) regions. We show that is the optimum value of Weber number which can support a gas cushion for the widest range of Reynolds numbers. The phase diagram is further divided into five sub-regions based on the shape of the drop and the gas film beneath it. The simulations can reproduce experimentally reported gas films of with excellent agreement spatially and temporally. Simulations also reproduce well-known scaling laws for a variety of parameters characterising the gas film. New scaling laws for the radial extent of the gas film as well as time taken for impact are derived. For higher Weber and Reynolds numbers, a bouncing drop captures a gas bubble inside it consistent with simple experiments carried out for water drops bouncing on superhydrophobic surfaces.

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IITH Creators:
IITH CreatorsORCiD
Dixit, Harish N
Item Type: Article
Additional Information: P.K.S. thanks the Ministry of Human Resource Developement for a PhD fellowship and H.N.D. thanks the Science and Engineering Research Board (SERB), Department of Science and Technology through grant ECR/2015/000086 for funding this research. We also thank discussions with Dr S. Mandre and Dr J. de Ruiter for helpful clarifications during the research. We thank Dr B. Karri for proofreading the manuscript which helped us improve the overall presentation. We also thank an anonymous referee for insightful feedback and providing us with many important references. We express our gratitude to Dr S. Popinet and other developers of Gerris without whose efforts this work would not have been possible.
Uncontrolled Keywords: Capillary numbers; Contact bouncing; Dimensionless parameters; Hydrophilic surfaces; Optimum value; Solid surface; Super-hydrophobic surfaces; Weber numbers
Subjects: Physics > Mechanical and aerospace
Divisions: Department of Mechanical & Aerospace Engineering
Depositing User: . LibTrainee 2021
Date Deposited: 02 Aug 2021 05:56
Last Modified: 17 Nov 2022 11:40
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