Insight into flickering/shedding in buoyant droplet-diffusion flame during interaction with vortex

Thirumalaikumaran, S. K.; Vadlamudi, Gautham; Basu, Saptarshi

doi:10.1016/j.combustflame.2022.112002

Cited by 5 publications

(2 citation statements)

References 19 publications

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“…Many studies [12][13][14][15] have shown that the buoyancy-induced flickering of flames is a hydrodynamic global instability rather than a convective instability. Interestingly, similar flickering phenomena were observed in buoyant jet and plume flows [16][17][18] and the wake of droplets and porous spheres flame [19][20][21]. Such axisymmetric periodic oscillation can be observed in premixed and partially premixed flames [22,23].…”

Section: Introductionsupporting

confidence: 60%

Dynamical Behavior of Small-Scale Buoyant Diffusion Flames in Externally Swirling Flows

Yang,

Ma,

Zhang

2024

Symmetry

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This study computationally investigates small-scale flickering buoyant diffusion flames in externally swirling flows and focuses on identifying and characterizing various distinct dynamical behaviors of the flames. To explore the impact of finite rate chemistry on flame flicker, especially in sufficiently strong swirling flows, a one-step reaction mechanism is utilized for investigation. By adjusting the external swirling flow conditions (the intensity R and the inlet angle α), six flame modes in distinct dynamical behaviors were computationally identified in both physical and phase spaces. These modes, including the flickering flame, oscillating flame, steady flame, lifted flame, spiral flame, and flame with a vortex bubble, were analyzed from the perspective of vortex dynamics. The numerical investigation provides relatively comprehensive information on these flames. Under the weakly swirling condition, the flames retain flickering (the periodic pinch-off of the flame) and are axisymmetric, while the frequency nonlinearly increases with the swirling intensity. A relatively high swirling intensity can cause the disappearance of the flame pinch-off, as the toroidal vortex sheds around either the tip or the downstream of the flame. The flicker vanishes, but the flame retains axisymmetric in a small amplitude oscillation or a steady stay. A sufficiently high swirling intensity causes a small Damköhler number, leading to the lift-off of the flame (the local extinction occurs at the flame base). Under the same swirling intensity but large swirling angles, the asymmetric modes of the spiral and vortex bubble flames were likely to occur. With R and α increasing, these flames exhibit axisymmetric and asymmetric patterns, and their dynamical behaviors become more complex. To feature the vortical flows in flames, the phase portraits are established based on the velocity information of six positions along the axis of the flame, and the dynamical behaviors of various flames are presented and compared in the phase space. Observing the phase portraits and their differences in distinct modes could help identify the dynamical behaviors of flames and understand complex phenomena.

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Section: Introductionsupporting

confidence: 60%

Dynamical Behavior of Small-Scale Buoyant Diffusion Flames in Externally Swirling Flows

Yang,

Ma,

Zhang

2024

Symmetry

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“…Results show that the flame stabilizes in the droplet wake when ignited in a flow at the Reynolds number, Re ∼ (45 and 67), whereas an enveloped flame was observed at Re ∼ 11 (lower Reynolds number). Likewise, Thirumalaikumaran, Vadlamudi & Basu (2022) and Pandey et al (2021) showed that local flow-field variations alter the droplet flame behaviour. The envelope-to-wake flame transition was observed when the burning droplet was incident with vortical structures.…”

Section: Introductionmentioning

confidence: 98%

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

Vadlamudi,

Aravind,

Basu

2023

J. Fluid Mech.

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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.

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Faster flicker of buoyant diffusion flames by weakly rotatory flows

Yang

Zhang

2023

Theor. Comput. Fluid Dyn.

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Insight into flickering/shedding in buoyant droplet-diffusion flame during interaction with vortex

Cited by 5 publications

References 19 publications

Dynamical Behavior of Small-Scale Buoyant Diffusion Flames in Externally Swirling Flows

Dynamical Behavior of Small-Scale Buoyant Diffusion Flames in Externally Swirling Flows

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

Faster flicker of buoyant diffusion flames by weakly rotatory flows

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