Vadlamudi, G and Thirumalaikumaran, SK and Basu, S (2021) Insights into the dynamics of wake flame in a freely falling droplet. In: Physics of Fluids, 33 (12).
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Abstract
The combustion of a freely falling dodecane droplet has been studied experimentally in a droptower-like facility under ambient conditions. A unique ignition mechanism is used by igniting the droplet in pendant mode and releasing it to fall freely. This unveils a different type of droplet wake flame behavior which is explored in this study. Initially, the droplet flame transitions from fully enveloped to a wake flame configuration due to forward extinction. The wake flame has similar characteristics as a laminar lifted triple-flame. As the droplet accelerates, the flame stand-off increases continuously. The change in wake flame topology and intensity occurs in two different regimes corresponding to different droplet diameters. A new non-dimensional parameter has been derived to account for the local balance between buoyancy and momentum diffusion that alters the fuel availability. To explain the flame topological evolutions and transitions for different droplet diameters and Reynolds numbers, a theoretical formulation has been proposed based on the momentum diffusion from surrounding due to relative motion. Further, at very high Reynolds number, flame stretching or shedding regime occurs, causing momentary spikes in flame intensity due to the interaction with asymmetric vortex shedding induced by the Bernard-Von Karman instability. Interestingly, the flame shedding height follows the buoyant flickering scaling, even for the momentum-dominant droplet wake flame. Additionally, the circulation build-up mechanisms are shown to be responsible for the flame shedding events for droplet wake flame at high Reynolds number. © 2021 Author(s).
| Item Type: | Journal Article |
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| Publication: | Physics of Fluids |
| Publisher: | American Institute of Physics Inc. |
| Additional Information: | The copyright for this article belongs to the Author. |
| Keywords: | Buoyancy; Combustion; Drops; Momentum; Reynolds number; Topology, Ambient conditions; Dodecane; Droplet diameters; Droplet flames; Falling droplet; Flame behaviors; Flame intensity; High Reynolds number; Ignition mechanisms; Momentum diffusion, Wakes |
| Department/Centre: | Division of Interdisciplinary Sciences > Interdisciplinary Centre for Energy Research Division of Mechanical Sciences > Mechanical Engineering |
| Date Deposited: | 06 Jan 2022 11:38 |
| Last Modified: | 06 Jan 2022 11:38 |
| URI: | http://eprints.iisc.ac.in/id/eprint/70823 |
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