EXP 1-4 Description
Axisymmetric drop impact dynamics on a wall film of the same liquid
Description of Study Test Case
A sketch of the general set-up of the experiment and the geometry is shown in Fig. 3 in Section Lib:EXP 1-4 Experimental Set Up while the principal quantities measured are given in Section Lib:EXP 1-4 Measurement Quantities and Techniques. The liquid used in the experiments is silicone oil (density ρ = 920 kg/m3, kinematic viscosity ν = 5 ⋅ 10-6 m2/s, surface tension σ = 0.0177 N/m) and the ambient gas is air (density 1.2 kg/m3, kinematic viscosity 1.52 ⋅ 10-5 m2/s). The film height h = 500 μm as well as the drop diameter D = 1.5 mm are kept fixed, resulting in the dimensionless film thickness δ = h/D = 0.33. The drop velocity U is varied from 1 to 3 m/s. Accordingly, the Weber number We = ρDU2/σ is in the range 78 – 702 while the Reynolds number Re = DU/ν is in the range 300 – 900, see Table 1.
| Impact energy | Impact velocity | Weber number | Reynolds number | Link for video download |
|---|---|---|---|---|
| Low | 1 m/s | 78.0 | 300 | Download S5_D1p5_H500_U1 |
| Moderate | 2 m/s | 311.9 | 600 | Download S5_D1p5_H500_U2 |
| High | 3 m/s | 701.7 | 900 | Download S5_D1p5_H500_U3 |
For each impact velocity a video is provided in Table 1 for download. The meaning of the file names is as follows: S5 = silicon oil with kinematic viscosity 5 mm^2/s, D1p5 = drop diameter 1.5 mm , H500 = film height 500 µm. The digit after U denotes the drop impact velocity in m/s, e.g. U3 = 3 m/s. The drop-film interaction in the three videos can be characterized as follows.
For the low energy impact the drop joins the liquid film smoothly without formation of a rim or crown. In this deposition regime, the drop spreads on the surface of the liquid film forming a disk-shaped structure. In the late stage, capillary waves propagate on the surface of the film without formation of a notable central dome.
For the moderate energy impact a rising crown is formed at the boundary between the residual and the initial film where there is a kinematic discontinuity due to the jump in both the film thickness and the local velocity field. The crown ascend continues as long as the inertial forces dominate the surface tension forces. The upper free rim of the crown remains stable and fully axisymmetric and the case corresponds to the crown formation without break-up regime. In the late stage after collapse of the crown, a dome like structure forms at the impact center without generation of a jet.
The case of the high energy impact corresponds to the crown formation without break-up regime as well. However, the increased magnitude of inertial forces causes the crown to grow much higher (approximately twice) as compared to the moderate energy impact. While the upper free rim remains axisymmetric during the ascend of the crown, slight deviations from axisymmetry can be noticed during the collapse of the crown. Moreover, the energy of the impact is high enough to form a central Worthington jet which emerges from the impact center. The central jet experiences rupture (pinch-off) and forms satellite droplets. These droplets bounce on the surface of the disturbed film before merging into it.
Contributed by: Milad Bagheri, Bastian Stumpf, Ilia V. Roisman, Cameron Tropea, Jeanette Hussong, Martin Wörner, Holger Marschall — Technical University of Darmstadt and Karlsruhe Institute of Technology
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