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Title: Drop impact on solids: contact-angle hysteresis filters impact energy into modal vibrations
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.  more » « less
Award ID(s):
1935590
PAR ID:
10311622
Author(s) / Creator(s):
; ;
Date Published:
Journal Name:
Journal of Fluid Mechanics
Volume:
923
ISSN:
0022-1120
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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