fragmentation of bubbles in turbulence by small eddies
TRANSCRIPT
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NI RESEARCH GROUP
Fragmentation of bubbles in turbulence by small eddies
Yinghe Qi
Noah Corbitt, Carl Urbanik, Shiyong Tan, Ashwanth Salibindla, Rui Ni
Department of Mechanical Engineering
Johns Hopkins University
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NI RESEARCH GROUP2
Fragmentation in turbulence
Villermaux Annu. Rev. Fluid Mech. (2007)Enders, et al. Marine pollution bulletin (2015)Li, C., et al. J. Geophys. Res.: Oceans 122.10 (2017): 7938-7957.Dean & Stokes. Nature. (2002)
Breaking wave
Fragmentation Size spectrum Interfacial area (mass transfer)Rise velocity (lifetime)Dispersion
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Kolmogorov-Hinze (KH) framework
3
Basic assumption: bubble is broken by the eddy with similar size
Large eddies only advect the bubble without deforming it
Small eddies effect can be filter by the bubble
KH theory --> bubble size is the only scale in the breakup problem
ππ =ππ’2π·
π~π ππ· 2/3π·
π=ππ2/3π·5/3
π
The critical Weber number ππππππππ~[0.59, 7.8]
Is this right?Can we ignore small eddy contribution?
Sevik & Park 1973; Deane & Stokes 2002; Martinez-Bazan et al.1999; Risso & Fabre 1998
Kolmogorvo 1949; Hinze 1955;
ππ > 1, breakups happen.
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NI RESEARCH GROUP
Introduction to the vortex ring collision
4
McKeown et al. 2018. PRF
Instability leads to two stagesFrom large scale to small scale
credit: Rodolfo Ostilla Monico (University of Houston)
Early
stage
Late
stage
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Experimental setup
5
Linear actuator, syringe pump and cameras are all synchronized.
Shake the box
Particle trajectory
Visual hull method
Bubble geometry and breakup
Tan et al. 2020., Mausk et al. 2019.
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Large vortex
100
101
10-3
10-2
10-1
100
101
10-3
10-2
10-1
ππ π = π’ π₯ + π β π’ π₯ 2
π ππ
From large to small scale
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NI RESEARCH GROUP 7
Bubble breakup modes
Primary breakup (slow and moderate)
π‘π = 34 ms
π‘π = 5 ms
Secondary breakup (rapid and violent)
Breakup time PDF
Can KH theory explain this?
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πππ =π π3π·
2π·
πππΞ© =
π ππ· 2π·
π
Secondary breakups generally have smaller weber number
Weber number (Kolmogorov-Hinze)
Weber number around the bubble
Secondary breakups are more violent. Expect larger Weber number
Why?
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Flow around the bubble
9
Filtered
large eddies
Remaining small eddies
Pri
mar
y b
reak
up
Seco
nd
ary
bre
aku
p
How to improve KH framework
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A new breakup model
10
Stress criterion:ππ’π
2 > π/π·π
Time criterion:
π·π/π’π < 2π ππ·3/96π
Minimum eddy velocity required to break a bubble
π«ππ«
α
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Eddy contribution
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Distribution of dissipation rate
Meneveau & Sreenivasan 1991Kolmogorov 1962
Sub-bubble-scale eddies are more important for bubble fragmentation.
Considering collision frequency
Distribution of eddy velocity
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Our experiment (vortex ring collision)
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Fully-developed turbulence
Vejrazka et al. 2018
Kolmogorov-Hinze framework
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Summary
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β’ Vortex ring collision provides a magic knife to separate different eddy scale
β’ Secondary breakups with smaller Weber number exhibit violent breakup mode
β’ Sub-bubble scale eddies play an important role in breakups
β’ A new bubble breakup model is proposed considering the eddy scale