Research Training Group 2160/1: Droplet Interaction Technologies

Università degli Studi di BergamoItaly

Università di TrentoItaly

Universität StuttgartGermany

Subproject C1: Micro and Macro Drop Impact Dynamics with Miscible Liquids

Scholar: R. Bernard, Institute of Aerospace Thermodynamics (ITLR), University of StuttgartSupervisors: G. Lamanna (University Stuttgart), N. Roth (University Stuttgart), S. Tonini (University Bergamo)

Two-Component Droplet Impact Upon Thin Films

Influence of the micro-dynamics on the large-scale features

Text

Coupling of the micro- and macro-visualisation techniques

Future Work

Investigation of Particular Features

Contact

Understanding of interplay between small-scale flowfeatures and overall macroscopic impact dynamics

Extension of the high-speed visualisation database fortwo-component droplet impacts

Development of micro-visualisation techniques to studythin film dynamics

Micro Particle Image Velocimetry (micro PIV)

Holes in the crown Crown bottom breakdown

[1] Geppert et al., Atomization and Sprays, 10.1615/AtomizSpr.2015013352, 2015.[2] Cossali et al., Experiments in Fluids, 22(6), 463-472, 1997.[3] Vander Wal et al., Experiments in Fluids 40, 53-59, 2006.[4] Bernard et al., 28th ILASS-Europe, accepted on 25.04.2017.

Two-perspective High-speed Shadowgraphy

Fig.5. Double-frame images of seeded thin film (left) and resultingvelocity and vorticity fields (right) during impact.

Micro visualisation techniques (Micro PIV, TIRFM)

High-speed shadowgraphy

Specific features of two-componentinteractions [1]

No clear triggering conditions

Observed for a droplet impact on a thin /very thin wall-film of a less viscous liquid

Generalized Deposition/Splashing Limit

References

tt + Δt

Experimental Setup:

Dropper

Impact area

Imaging system

Fig.1 Experimental setup of the two-perspective high-speed shadowgraphy imaging system. Adapted from [1]

Inverted microscope

Micro PIV Setup:

Double-pulsedNd:YAG Laser

CCD Camera

Velocity field in the thin film

- Boundary layer / Viscous losses- Feeding of the crown- Liquids distribution Thin film buffer / Mixture

Growth / Break-downOutcome

Fig.7. Crown bottom breakdown of oil-oil combinations.Fig.6. Holes in the crown for hexadecane-oil interactions.

Ronan BERNARDEmail: ronan.bernard@itlr.uni-stuttgart.deTelephone: +49 (0) 711 685-62325Fax: +49 (0) 711 685-62317

Institute of Aerospace ThermodynamicsUniversity of Stuttgart

Pfaffenwaldring 3170569 Stuttgart

• Droplet detachment by gravity• Impact velocity adjusted with the fall height

• Triggered by a laser light barrier• CMOS Camera with 20,000 fps• Simultaneous recording of frontal and

lateral view

• Thin film made from metallic ring glued onsmooth sapphire plate

• Non intrusive measurement of the filmthickness with Confocal Chromatic Imaging(CCI) technique

Averaged properties lead to a good repartition towards the limit

Fig. 4. Unified deposition/splashing limit (black surface) [4]Left: view from the top (splashing, red symbols)Right: view from the bottom (deposition, blue symbols)

Unified deposition/splashing limit of one- and two-component experiments

𝑂ℎ 𝑅𝑒1.29 = (4400 + 8900 𝛿1.44) ൗ1 1.6

• Color Legend: Splashing, Deposition• Accuracy of the limit of 75.6% over 2197 experiments

Measurements of the velocity field in the thin film during impact

Extension of the database for two-component interactions of high viscous liquids

• Magnification 5x – 40x• Micrometric Z-translation

Fig.2. Common mapping of one- and two-component droplet impacts upon thin films in (Oh, Re, δ) from the referenced sources. [4]

Unified mapping of one- and two-component experiments

• Large database from literature [1-3]• Study of two-component interactions (silicon oil combinations and hexadecane)• Averaged liquid properties of the droplet and the wall-film for Oh and Re

𝑅𝑒 =2 𝑉 𝐷

𝜐𝑓 + 𝜐𝑑

𝑂ℎ =𝜐𝑓 + 𝜐𝑑

2

𝜌𝑓 + 𝜌𝑑

𝐷 (𝜎𝑓 + 𝜎𝑑)