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Effect of wettability on the water entry problem of aluminum spheres

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Abstract

We investigated the hydrodynamics of water entry by aluminum spheres varying in wettability, assisted by nano/microscaled surface morphology. A wide range of contact angle (C.A.: 0° ≤ θ0 < 170°) on the test spheres was prepared via inexpensive single-step anodization method. The water entry events: Splash and cavity formation, were visualized by a high-speed camera to understand the fast transient features affected by the surface wettability. In terms of hydrodynamics, cavity formation and air entrainment during the water entry were analyzed via dynamic wetting of liquid film flow along the sphere surface. It was confirmed that wettability was a determinant factor of both splash shape and cavity formation, especially in hydrophobic condition (90° ≤ θ0). Furthermore, the analysis of dynamic contact angle of liquid film front in this study was able to classify the water entry events more detail than previous literature. In addition, we also recorded audio signals to evaluate acoustic pressures produced by the impact between spheres and water pool. The audio signals, which are expected to be proportional to acoustic pressures, differed when hydrophilic and hydrophobic spheres entered water.

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Abbreviations

θ :

Contact angle [Rad]

v, U :

Velocity [m/s]

ξ:

Numerical prefactor [-]

σ :

Surface tension [N/m]

µ :

Viscosity [Pas]

r :

Radius of sphere [m]

α :

Numerical prefactor [-]

L c :

Logarithmic ratio lengths [-]

0:

Static

d :

Dynamic

*:

Threshold

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Acknowledgments

This research was supported by the Science Research Program of the National Research Foundation of Korea (NRF) funded by the Ministry of Education (grant no. 2016R1A6A3 A03008942).

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Authors and Affiliations

  1. Department of Precision Mechanical Engineering, Kyungpook National University, Sangju, Korea

    Seolha Kim

  2. Aircraft System Technology Group, KITECH, Cheonan, 31056, Korea

    Dongseob Kim

  3. Versatile Reactor System Technology Development Division, KAERI, Daejeon, 34057, Korea

    Hyungmo Kim

Authors
  1. Seolha Kim
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  2. Dongseob Kim
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  3. Hyungmo Kim
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Correspondence to Hyungmo Kim.

Additional information

Recommended by Editor Chang-Soo Han

SeolHa Kim graduated from POSTECH, (South Korea) for Bachelor (Mechanical Engineering) to and Doctor degree (Nuclear Engineering). He worked in Korea Atomic Energy Research Institute and Chinese Academy of Science for researcher. Currently, he is working in Kyungpook National University as an Assistant Professor.

Dongseob Kim received his Ph.D. in Mechanical Engineering from POSTECH in 2010. Currently, he is a Principal Researcher in the Aircraft System Technology Group at KITECH working. His main research interests focus on the fields of analysis and fabrication of nanostructures for mechanical characterization and nanofabrications for metamaterials and nanomechanics.

Hyungmo Kim received his Ph.D. (Mechanical Engineering) from POSTECH. He is currently a Senior Researcher in the Advanced Reactor Development Team of Korea Atomic Energy Research Institute. His research interests include various kinds of heat and mass transport phenomena in practical systems.

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Kim, S., Kim, D. & Kim, H. Effect of wettability on the water entry problem of aluminum spheres. J Mech Sci Technol 34, 1257–1263 (2020). https://doi.org/10.1007/s12206-020-0224-2

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  • DOI: https://doi.org/10.1007/s12206-020-0224-2

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