Article contents
Drop impact on solids: contact-angle hysteresis filters impact energy into modal vibrations
Published online by Cambridge University Press: 21 July 2021
Abstract
The energetics of drop deposition are considered in the capillary-ballistic regime characterized by high Reynolds number and moderate Weber number. Experiments are performed impacting water/glycol drops onto substrates with varying wettability and contact-angle hysteresis. The impacting event is decomposed into three regimes: (i) pre-impact, (ii) inertial spreading and (iii) post contact-line (CL) pinning, conveniently framed using the theory of Dussan & Davis (J. Fluid Mech., vol. 173, 1986, pp. 115–130). During fast-time-scale inertial spreading, the only form of dissipation is CL dissipation ($\mathcal {D}_{CL}$). High-speed imaging is used to resolve the stick-slip dynamics of the CL with
$\mathcal {D}_{CL}$ measured directly from experiment using the
$\Delta \alpha$-
$R$ cyclic diagram of Xia & Steen (J. Fluid Mech., vol. 841, 2018, pp. 767–783), representing the contact-angle deviation against the CL radius. Energy loss occurs on slip legs, and this observation is used to derive a closed-form expression for the kinetic K and interfacial
$\mathcal{A}$ post-pinning energy
$\{K+\mathcal {A}\}_p/\mathcal {A}_o$ independent of viscosity, only depending on the rest angle
$\alpha _p$, equilibrium angle
$\bar {\alpha }$ and hysteresis
$\Delta \alpha$, which agrees well with experimental observation over a large range of parameters, and can be used to evaluate contact-line dissipation during inertial spreading. The post-pinning energy is found to be independent of the pre-impact energy, and it is broken into modal components with corresponding energy partitioning approximately constant for low-hysteresis surfaces with fixed pinning angle
$\alpha _p$. During slow-time-scale post-pinning, the liquid/gas (
$lg$) interface is found to vibrate with the frequencies and mode shapes predicted by Bostwick & Steen (J. Fluid Mech., vol. 760, 2014, pp. 5–38), irrespective of the pre-impact energy. Resonant mode decay rates are determined experimentally from fast Fourier transforms of the interface dynamics.
- Type
- JFM Papers
- Information
- Copyright
- © The Author(s), 2021. Published by Cambridge University Press
References
REFERENCES
- 9
- Cited by