Abstract
Author(s): Hariharan, SB; Hu, Y; Gollner, MJ; Oran, ES | Abstract: The relative influence of circulation and buoyancy on fire whirls (FWs), blue whirls (BWs), and the transition between these regimes of a whirling flame is investigated using a combination of experimental data and scaling analyses. FWs are whirling, turbulent, cylindrical yellow (sooting) flame structures that form naturally in fires and are here created in laboratory experiments. In contrast, a BW is a laminar, blue flame (nonsooting) with an inverted conical shape. Measurements of the circulation and heat-release rate are combined with measurements of the flame geometry, defined by the flame width and the height, to provide characteristic length scales for these whirling-flame regimes. Using these, a nondimensional circulation (Γf) and a heat-release rate (Qf) were defined and shown to correspond to azimuthal and axial (buoyancy driven) momenta, respectively. The ratio R=Γf/Qf, a quantity analogous to the swirl number used to characterize swirling jets, was evaluated for FWs and BWs. For FWs, Rl1, so that axial momentum is greater than azimuthal momentum and the flame is dominated by buoyant momentum. For BWs, Rg1, so that the flame is circulation dominated. This is argued to be consistent with vortex breakdown being an important part of the transition of FWs to BWs. This work presents a basis for predicting when a BW will form and remain a stable regime.
Highlights
The interaction of reacting buoyant plumes and swirling flow fields gives rise to structures called fire whirls
The purpose of this work is to test this hypothesis: The flow field of the blue whirl is a state of vortex breakdown that occurs when the local azimuthal momentum becomes higher than the axial momentum, and this blue whirl retains properties of the bubble mode
We find that when the flow field is dominated by buoyancy, the traditional fire whirl develops, and when circulation dominates, there is a transition to the blue whirl
Summary
The interaction of reacting buoyant plumes and swirling flow fields gives rise to structures called fire whirls. HARIHARAN, HU, GOLLNER, AND ORAN effects they can have in urban and wildland fires [1,2,3] Both the structure and the dynamic behavior of fire whirls are dominated by the effects of buoyancy, which arises from heat release, and by circulation, determined by the level of ambient swirl. In laboratory-scale experimental investigations, the combination of the heat-release rate (Q ) and circulation ( ) can be controlled to determine the shapes of fire whirls, which have been classified into a number of regimes [4]. The blue whirl is a small, soot-free flame that was first observed in an experimental study of fire whirls formed on a water surface [5]. Various combinations of fuel flow rate (V ) and gap size (S) were used to generate fire whirls and blue whirls. The flow velocity into the enclosure was measured at selected axial (vertical) locations using a DANTEC 54T42 Mini
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
