Buoyant Tsuji diffusion flames: global flame structure and flow field. (25th July 2020)

• Record Type: Journal Article
• Authors: Donini, Mariovane S.; Cristaldo, Cesar F.; Fachini, Fernando F.
• Is Part Of: Journal of fluid mechanics. Volume 895(2020)
• Publication Date: 2020-07-25
• Subjects: laminar reacting flows, -- buoyancy-driven instability, -- vortex dynamics; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2020.266
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract : Abstract : The present work analyses how buoyancy is impacting the topology of diffusion flames established around a horizontal cylindrical burner. The flow conditions are chosen such that the system is subjected to negative and positive buoyant forces. It is proposed in this study to investigate the effect of a modulation of the balance between these buoyant forces on the flame structure by varying the temperature of the ambient atmosphere. More specifically, conditions are sought for establishing a buoyant Tsuji diffusion flame characterized by a very low level of strain rate in its lower part (i.e. below the burner). To understand the fundamental mechanisms controlling the whole flame topology, a model is proposed which assumes steadiness and incompressibility of the flow while retaining buoyancy effects in the momentum balance. The results showed that an increase of the ambient temperature leads to the appearance of a counterflow zone below the burner where the flame is undergoing very low levels of strain rate. The overall flame proves to be shorter than its counterpart observed in the forced convection regime. In addition, it is shown that an order of magnitude analysis is able to recover the sensitivity of the flame behaviour to the Péclet and Froude numbers as well as to the combustion parameters. In a certain range of the ambient-atmosphere temperature, the flow field changes dramatically: for the same boundary conditions, there are two steady-state solutions which depend on the initial conditions, i.e. the system presents a hysteresis.