1 Introduction
Parameter | Values |
---|---|
Density of water ρ (kg/m3) | 999 |
Viscosity of water μ (kg/m.s) | 0.00099 |
Surface tension of water σ (kg/s2) | 0.0727 |
Droplet velocity U (m/s) | 1.40, 1.98, 2.43, 2.80, 3.13 |
Ohnesorge number Oh (–) | 0.002 |
Reynolds number Re (–) | 4900, 6900, 8500, 9800, 11,000 |
Froude number Fr (–) | 57, 114, 171, 228, 285 |
Film thickness h* (–) | 0.43, 0.86, 1.29 |
Weber number We (–) | 94, 189, 283, 378, 472 |
K = We OH
−0.4 (–) | 1138, 2277, 3415, 4554, 5693 |
2 Experimental procedure and methods
3 BB-LIF technique
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Case 1: Both droplet and film were doped with the fluorescent dye.
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Case 2: Only the film was doped.
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Case 3: Only the droplet was doped.
4 Results
4.1 Evolution of the cavity
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Prompt splash: small droplets can be seen in Fig. 3a, f, k showing that the splash contains liquid from both the film and the droplet. Droplet fluid is spread over the surface of the crater and runs up the sides.
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Crown formation: Fig. 3b, g, l shows that the crown also contains liquid from the droplet and the initiation of secondary droplet formation can be seen.
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Crown ligaments formed: as shown in Fig. 3c, h, m, both film and droplet liquid are entrained into the secondary droplets generated from the crown break-up.
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Secondary droplet impact: as shown in Fig. 3d, i, n, secondary droplets produce craters on surface of film after impact and liquid from film and droplet are draining back towards the centre of the crater.
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Jet formation: as shown in Fig. 3e, j, o, jet is formed of film and droplet liquid.
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Prompt splash: as shown in Fig. 4a, f, k, streaks (possibly ligaments) are seen around the point of impact containing film and droplet liquid.
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Crown formation: as shown in Fig. 4b, g, l, crown is formed, but in this case, the crown is sloped inwards. Droplet liquid spreads over surface of crater and up walls, but not as far as the surface and so is not collected in crown. Droplet liquid from prompt splash collects outside the crown.
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Crown receding: as shown in Fig. 4c, h, m, crown begins to recede. No secondary droplets are produced in this case.
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Fluid draining: as shown in Fig. 4d, i, n, droplet liquid and film liquid drain towards the centre of the crater to initiate the formation of the Worthington jet.
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Jet formation: as shown in Fig. 4e, j, o, surrounded by ripple wave that propagates out from the impact, most of the droplet fluid has collected in the jet.