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: [email protected]: +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)
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