Simultaneous observation of organized density structures and the visible field in pool fires

Schönbucher, Axel; Arnold, Benjamin; Banhardt, V.; Bieller, V.; Kasper, H. M.; Kaufmann, Michael; Lucas, Richard W.; Schieß, Norbert

doi:10.1016/s0082-0784(88)80234-0

Cited by 19 publications

(6 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Here, different 9 single pool flames with varying (4.9, 9.8 and 19.6 m/s 2 ) and (10, 15, 20, 30 mm) were simulated, and the simulation results in Fig. 3 agree well with previous experiments [42][43][44][45] and the scaling relation [24,40], verifying that the present numerical methods are suitable for studying the flickering of pool flames. To study the essence of dual flickering flames, it is necessary to summarize the existing perspectives on interpreting the unsteady characteristics of a single flickering flame.…”

Section: Flckering Of a Single Pool Flamesupporting

confidence: 83%

Vortex-dynamical interpretation of anti-phase and in-phase flickering of dual buoyant diffusion flames

2019

View full text Add to dashboard Cite

Anti-phase and in-phase flickering modes of dual buoyant diffusion flames were numerically investigated and theoretically analyzed in this study. Inspired by the flickering mechanism of a single buoyant diffusion flame, for which the deformation, stretching, or even pinch-off of the flame surface result from the formation and evolution of the toroidal vortices, we attempted to understand the antiphase and in-phase flickering of dual buoyant diffusion flames from the perspective of vortex dynamics.The interaction between the inner-side shear layers of the two flames was identified to be responsible for the different flickering modes. Specifically, the transition between anti-phase and in-phase flickering modes can be predicted by a unified regime nomogram of the normalized flickering frequency versus a characteristic Reynolds number, which accounts for the viscous effect on vorticity diffusion between the two inner-side shear layers. Physically, the transition of the vortical structures from symmetric (in-phase) to staggered (anti-phase) in a dual-flame system can be interpreted as being similar to the mechanism causing flow transition in the wake of a bluff body and forming the Karman vortex street.

show abstract

Section: Flckering Of a Single Pool Flamesupporting

confidence: 83%

Vortex-dynamical interpretation of anti-phase and in-phase flickering of dual buoyant diffusion flames

2019

View full text Add to dashboard Cite

show abstract

“…The phenomenon is dominated by, but not solely dependent upon, buoyancy. I n contrast, recent studies of the formation of organized structures in pool fires by Zukoski, Cetegen & Kubota (1984) and Schonbucher et al (1986) indicate that the natural frequency in this case does scale with the buoyancy timescale of the flow over a wide range of fire diameters. From a study of this work it appears that one might understand the scaling properties of flickering flames by distinguishing various cases on the basis of how buoyancy is released near the jet exit.…”

Section: Introductionmentioning

confidence: 69%

Investigation of a co-flowing buoyant jet: experiments on the effect of Reynolds number and Richardson number

Subbarao

Cantwell

1992

J. Fluid Mech.

View full text Add to dashboard Cite

Experiments have been carried out on a vertical jet of helium issuing into a co-flow of air at a fixed exit velocity ratio of 2.0. At all the experimental conditions studied, the flow exhibits a strong self-excited periodicity. The natural frequency behaviour of the jet, the underlying flow structure, and the transition to turbulence have been studied over a wide range of flow conditions. The experiments were conducted in a variable-pressure facility which made it possible to vary the Reynolds number and Richardson number independently. A stroboscopic schlieren system was used for flow visualization and single-component laser-Doppler anemometry was used to measure the axial component of velocity. The flow exhibits several interesting features. The presence of co-flow eliminates the random meandering typical of buoyant plumes in a quiescent environment. The periodicity of the helium jet under high-Richardson-number conditions is striking. Under these conditions transition to turbulence consists of a rapid but highly structured and repeatable breakdown and intermingling of jet and free-stream fluid. At Ri = 1.6 the three-dimensional structure of the flow is seen to repeat from cycle to cycle. The point of transition moves closer to the jet exit as either the Reynolds number or the Richardson number increases. The wavelength of the longitudinal instability increases with Richardson number. At low Richardson numbers, the natural frequency scales on an inertial timescale, τ1 = D/Uj where D is the jet diameter and Uj is the mean jet exit velocity. At high Richardson number, the natural frequency scales on a buoyancy timescale, τ2 = [ρjD/g(ρ∞ -ρj)]½ where g is the gravitational acceleration and ρj and ρ∞ are the jet and free-stream densities respectively. The transition from one flow regime to another occurs over a narrow range of Richardson numbers from 0.7 to 1. A buoyancy Strouhal number is used to correlate the high-Richardson-number frequency behaviour.

show abstract

“…In general, for a given burner and fuel type, oscillation has been noted to begin at a particular flow rate, although Maxworthy [8] has clearly established this 'setting in point' of oscillatory nature to be a small range of flow rates. This phenomenon has mostly been associated with the heated jet flow or plume generated by the flame and the subsequent formation of large vortices which cause a visible fluctuation in the flame height [9,10]. Katta et al [11] have presented an important summary paper on the numerical computation of axisymmetric diffusion flames that exhibit oscillatory trends of interest in this study.…”

Section: Introductionmentioning

confidence: 94%

Dynamic Characterization of Candle Flame

Ghosh

Mondal

et al. 2010

International Journal of Spray and Combustion Dynamics

View full text Add to dashboard Cite

The present work focuses on studying the flickering of a candle placed in a hollow cylindrical glass tube. Variations in flame area and intensity have been studied as the oscillating parameters of the flame with a camera and a Photomultiplier tube (PMT), and results have been found to be indicative of the presence of some well defined peaks in the amplitude spectrum of the flame intensity. Tests have been carried out with a range of candle diameters for the same glass tube giving similar results. Fluctuations in fractal dimension of the flame structure have also been studied in the course of the work. The time series data generated by processing camera images and also the PMT voltage output has been studied for existence of periodicity in the signal recorded. The correlation dimension has been determined for a number of experiments to characterize the dynamics of the signal.

show abstract

Simultaneous observation of organized density structures and the visible field in pool fires

Cited by 19 publications

References 6 publications

Vortex-dynamical interpretation of anti-phase and in-phase flickering of dual buoyant diffusion flames

Vortex-dynamical interpretation of anti-phase and in-phase flickering of dual buoyant diffusion flames

Investigation of a co-flowing buoyant jet: experiments on the effect of Reynolds number and Richardson number

Dynamic Characterization of Candle Flame

Contact Info

Product

Resources

About