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Insights into the flame transitions and flame stabilization mechanisms in a freely falling burning droplet encountering a co-flow

Published online by Cambridge University Press:  18 December 2023

Gautham Vadlamudi Open the ORCID record for Gautham Vadlamudi [Opens in a new window] ,
Akhil Aravind Open the ORCID record for Akhil Aravind [Opens in a new window]  and
Saptarshi Basu Open the ORCID record for Saptarshi Basu [Opens in a new window]
Gautham Vadlamudi
Affiliation:
Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India
Akhil Aravind
Affiliation:
Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India
Saptarshi Basu*
Affiliation:
Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India Interdisciplinary Centre for Energy Research (ICER), Indian Institute of Science, Bangalore 560012, India
*
†Email address for correspondence: sbasu@iisc.ac.in
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Abstract

The present study investigates the flame dynamics of a contactless burning fuel droplet under free fall subjected to a co-flow. The dynamic external relative flow established due to co-flow and droplet acceleration results in a series of droplet flame transitions. Different flame structures were observed, including a wake flame, reversed wake flame and enveloped flame. Following ignition, the droplet is allowed to fall through the central tube of a co-flow arrangement, and, at its exit, the droplet flame encounters the co-flow. The wake flame, which was established based on the droplet's instantaneous velocity of descent, encounters the abrupt relative velocity jump due to the co-flow. This causes the droplet flame to go through various transitions as it approaches equilibrium with the surrounding flow. Once it equilibrates, the droplet flame evolves in response to the instantaneous relative flow velocity. The droplet flame evolves by altering both its shape and the stabilization mechanism. Two stabilization mechanisms were identified for the droplet wake flame: edge-flame stabilization and bluff-body stabilization. The stabilization mechanism for different flame structures and the transition events have been theoretically analysed, and the relation between flame shape evolution and flow velocity has been determined based on the flow-field characteristics at the corresponding Re (Reynolds number) range. Furthermore, these correlations are employed in a mathematical formulation based on the spring–mass analogy, which predicts the droplet flame evolution after encountering the co-flow, including all the transition events.

JFM classification

Drops and Bubbles: Drops Multiphase and Particle-laden Flows: Reacting multiphase flow Reacting Flows: Combustion
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 977 , 25 December 2023 , A29
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Copyright
© The Author(s), 2023. Published by Cambridge University Press

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Supplementary material: File

Vadlamudi et al. supplementary movie 1

Sequence of flame transitions in a freely falling burning droplet with a co-flow velocity of v_(o,i)=2.2 m/s.
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File 1.2 MB
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Vadlamudi et al. supplementary movie 2

Sequence of flame transitions in a freely falling burning droplet with a co-flow of velocity v_(o,i)=3 m/s.
Download Vadlamudi et al. supplementary movie 2(File)
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Supplementary material: File

Vadlamudi et al. supplementary movie 3

Sequence of flame transitions in a freely falling burning droplet with a co-flow of velocity v_(o,i)=4 m/s.
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File 3 MB
Supplementary material: File

Vadlamudi et al. supplementary material 4

Vadlamudi et al. supplementary material
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