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Droplets bouncing on a wet, inclined surface
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10.1063/1.4771605
/content/aip/journal/pof2/24/12/10.1063/1.4771605
http://aip.metastore.ingenta.com/content/aip/journal/pof2/24/12/10.1063/1.4771605
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

A drop impacts an inclined coated surface and splits into four droplets. (a) Superposition of successive frames, taken at 300 fps, reveals the trajectory of the droplets. (b) The initial drop, before impact (time t = −7 ms). (c) The satellite droplets formed after impact (time t = 16 ms). Dimensionless parameters are , , and α = 14°.

Image of FIG. 2.
FIG. 2.

Impact scenarios at different Weber number , as revealed through a superposition of successive frames separated by δt milliseconds. (a) , δt = 10 ms. (b) , δt = 6 ms. (c) , δt = 4 ms. (d) , δt = 4 ms. Other dimensionless parameters are , and α = 14°. A detailed analysis of these impacts is found in Fig. 4.

Image of FIG. 3.
FIG. 3.

Shade code used in our presentation of experimental results. Different symbols correspond to different Ohnesorge numbers (between 0.007 and 0.35), while the shade indicates the value of the inclination angle α. Experiments with slightly different values of are grouped together with the same symbol; the dashed rectangle indicates the region described by the symbol. In subsequent figures, is denoted by bold symbols. The satellite droplets have a smaller , and so are represented by plain symbols.

Image of FIG. 4.
FIG. 4.

Bouncing, splitting, and merging: (a) , (b) , (c) , (d) and (e) , (f) . The other parameters are fixed for each droplet impact (α = 14°, and ). The frames are taken at identical times after impact, normalized by the capillary time τσ = 12.4 ms and indicated in the left column.

Image of FIG. 5.
FIG. 5.

Volume of the satellite droplets Ω s normalized by the volume of the impacting drop Ω, as a function of the incident normal Weber number . Other parameters are , and α = 14°. (Blue circle) Main droplet. (Red circle) Worthington satellite droplets, ejected above the main drop at t ≃ 0.7τσ. (Green circle) Satellite droplets from the pinch off, ejected below the main drop at t ∈ [1.16, 1.48]τσ. (Black square) Total volume ejected after impact.

Image of FIG. 6.
FIG. 6.

Normalized contact time t c σ as a function of the incident normal Weber number in the case of complete bouncing. Symbols are defined in Figure 3.

Image of FIG. 7.
FIG. 7.

Bouncing is seen as a black box that modifies the trajectory of the center-of-mass of the droplet, changing the velocity from to .

Image of FIG. 8.
FIG. 8.

Normalized time delay Δt/t c as a function of the incident normal Weber number . Symbols are defined in Figure 3.

Image of FIG. 9.
FIG. 9.

Slip length ΔL, normalized by the prediction ΔL 0 [Eq. (2)], as a function of the incident normal Weber number We 1n . Symbols are defined in Figure 3.

Image of FIG. 10.
FIG. 10.

Normal coefficient of restitution: Ratio of the normal Weber number after and before impact, as a function of . The dashed curve corresponds to Eq. (3) with . Symbols are defined in Figure 3.

Image of FIG. 11.
FIG. 11.

Prefactor as defined in the scaling law (3). Symbols are defined in Figure 3.

Image of FIG. 12.
FIG. 12.

Tangential coefficient of restitution: ratio of the tangential Weber number after and before impact, as a function of . Symbols are defined in Figure 3.

Image of FIG. 13.
FIG. 13.

Corrected tangential coefficient of restitution [defined in Eq. (4)], as a function of . The dashed line corresponds to Eq. (5). Symbols are defined in Figure 3.

Image of FIG. 14.
FIG. 14.

Time evolution of the energy, for : (a) and (b) and (c) and (d) . In (a) and (c), the snapshots are taken every 3 ms, the third frame corresponding to the impact time (t = 0). In (b) and (d), the dashed and solid lines represent the surface energy of the droplet and the mechanical energy (kinetic + gravity) of its center-of-mass.

Image of FIG. 15.
FIG. 15.

Stored energy E S , normalized by 4πR 2σ, as a function of the input Weber number , for . The solid line corresponds to the scaling law . Error bars are smaller than the symbol size.

Image of FIG. 16.
FIG. 16.

Output Weber number as a function of the stored energy E S normalized by 4πR 2σ. The solid line corresponds to the scaling law . Error bars are smaller than the symbol size.

Image of FIG. 17.
FIG. 17.

Snapshots of the impacts corresponding to the experiments depicted in Fig. 14 [ , (a) and (b) ]. Frames are separated by 1.33 ms. Time is increasing from left to right on the first row, then from right to left on the second row, in order to reveal the strong time asymmetry at .

Image of FIG. 18.
FIG. 18.

Detail of the compression phase for the experiment depicted in Figs. 14(c) and 14(d) and Fig. 17(b) [ and ]. Frames are separated by 0.33 ms.

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/content/aip/journal/pof2/24/12/10.1063/1.4771605
2012-12-13
2014-04-21
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Droplets bouncing on a wet, inclined surface
http://aip.metastore.ingenta.com/content/aip/journal/pof2/24/12/10.1063/1.4771605
10.1063/1.4771605
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