Droplet breakup is a complex process involving interfacial instability and transport across a wide range of length and time scales. Fundamental studies of shock-droplet interaction provide valuable insight into the physical processes behind droplet breakup at high Weber and Reynolds numbers. Many high-speed applications such as liquid-fueled detonations and hypersonic hydrometeor impacts involve small droplets under high Weber numbers and/or unsteady conditions. The work presented here will explore deformation and hydrodynamics leading to breakup for small droplets (< 200μm) at high Weber numbers. An experimental campaign is presented whereby droplet deformation is measured at high temporal and spatial resolution. Small rapidly evaporating droplets (≈ 150μm) at Weber numbers in excess of 1000 are studied. High-speed
(sub-microsecond image times) shadowgraphy provides measurement of the droplet deformation rate, acceleration, and breakup timing. DNS results are presented to further explore deformation rates for smaller droplets (≈ 5μm). Deformation rates are compared with existing models for both experimental and simulation cases. This ongoing work will provide additional data from which our understanding of complex droplet phenomena may be advanced and applied to physical systems.
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Evaporation and breakup effects in the shock-driven multiphase instability
Evaporation and breakup of liquid droplets are common in many applications of the shock-driven multiphase instability (SDMI), such as in liquid-fuelled detonation engines, multiphase ejector pumps and turbines and explosive dispersal of liquid particles (i.e. chemical or biological agents). In this paper, the effects of evaporation and breakup of droplets on the mixing induced by the SDMI are considered through simulations and compared with experimental results. The evaporation model is validated against previous experimental data. The capabilities of the simulations and particle models are then demonstrated through a qualitative comparison with experimental results where breakup effects are negligible (i.e. small droplets). The simulation results are explored further to quantify the effects of evaporation (i.e. mixing enhancement) in the SDMI, providing further insight into the experimental results. A new breakup model, derived from previous works, is then presented for low Reynolds number (below 500), low Weber number (below 100) droplets in a shock-driven multiphase instability. The breakup model capabilities are then demonstrated through a comparison with experimental results where breakup effects are significant (larger droplet sizes). Finally, the simulation results are used to highlight the importance of breakup parameters on the evaporation rate and large-scale mixing in the SDMI. Overall, it is shown that evaporation is enhanced by the large-scale hydrodynamics instability, the SDMI, and that breakup of the droplets significantly increases the strength of the instability, and rate of droplet evaporation.
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- PAR ID:
- 10269838
- Date Published:
- Journal Name:
- Journal of fluid mechanics
- Volume:
- 908
- ISSN:
- 1469-7645
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/https://doi.org/10.1017/jfm.2020.871
