scholarly journals Data assimilation using high-speed measurements and LES to examine local extinction events in turbulent flames

2019 ◽  
Vol 37 (2) ◽  
pp. 2259-2266 ◽  
Author(s):  
Jeffrey W. Labahn ◽  
Hao Wu ◽  
Bruno Coriton ◽  
Jonathan H. Frank ◽  
Matthias Ihme
Keyword(s):  
Data Assimilation ◽  
High Speed ◽  
Turbulent Flames ◽  
Local Extinction ◽  
Extinction Events

The Structure and Propagation Mechanism of Turbulent Flames in High Speed Flow

1955 ◽  
Vol 25 (8) ◽  
pp. 377-384 ◽  
Author(s):  
MARTIN SUMMERFIELD ◽  
SYDNEY H. REITER ◽  
VICTOR KEBELY ◽  
RICHARD W. MASCOLO
Keyword(s):  
High Speed ◽  
Turbulent Flames ◽  
Propagation Mechanism ◽  
High Speed Flow ◽  
Speed Flow

The Effect of Lewis Number on Instantaneous Flamelet Speed and Position Statistics in Counter-Flow Flames With Increasing Turbulence

2017 ◽  
Author(s):  
Sean D. Salusbury ◽  
Ehsan Abbasi-Atibeh ◽  
Jeffrey M. Bergthorson
Keyword(s):  
Flame Front ◽  
Turbulence Intensity ◽  
High Speed ◽  
Rayleigh Scattering ◽  
Turbulent Flame ◽  
Lewis Number ◽  
Turbulent Flames ◽  
Flame Speed ◽  
Laminar Flames ◽  
Counter Flow

Differential diffusion effects in premixed combustion are studied in a counter-flow flame experiment for fuel-lean flames of three fuels with different Lewis numbers: methane, propane, and hydrogen. Previous studies of stretched laminar flames show that a maximum reference flame speed is observed for mixtures with Le ≳ 1 at lower flame-stretch values than at extinction, while the reference flame speed for Le ≪ 1 increases until extinction occurs when the flame is constrained by the stagnation point. In this work, counter-flow flame experiments are performed for these same mixtures, building upon the laminar results by using variable high-blockage turbulence-generating plates to generate turbulence intensities from the near-laminar u′/SLo=1 to the maximum u′/SLo achievable for each mixture, on the order of u′/SLo=10. Local, instantaneous reference flamelet speeds within the turbulent flame are extracted from high-speed PIV measurements. Instantaneous flame front positions are measured by Rayleigh scattering. The probability-density functions (PDFs) of instantaneous reference flamelet speeds for the Le ≳ 1 mixtures illustrate that the flamelet speeds are increasing with increasing turbulence intensity. However, at the highest turbulence intensities measured in these experiments, the probability seems to drop off at a velocity that matches experimentally-measured maximum reference flame speeds in previous work. In contrast, in the Le ≪ 1 turbulent flames, the most-probable instantaneous reference flamelet speed increases with increasing turbulence intensity and can, significantly, exceed the maximum reference flame speed measured in counter-flow laminar flames at extinction, with the PDF remaining near symmetric for the highest turbulence intensities. These results are reinforced by instantaneous flame position measurements. Flame-front location PDFs show the most probable flame location is linked both to the bulk flow velocity and to the instantaneous velocity PDFs. Furthermore, hydrogen flame-location PDFs are recognizably skewed upstream as u′/SLo increases, indicating a tendency for the Le ≪ 1 flame brush to propagate farther into the unburned reactants against a steepening average velocity gradient.

scholarly journals High-speed, three-dimensional tomographic laser-induced incandescence imaging of soot volume fraction in turbulent flames

2016 ◽  
Vol 24 (26) ◽  
pp. 29547 ◽  
Author(s):  
Terrence R. Meyer ◽  
Benjamin R. Halls ◽  
Naibo Jiang ◽  
Mikhail N. Slipchenko ◽  
Sukesh Roy ◽  
...  
Keyword(s):  
High Speed ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Soot Volume Fraction ◽  
Turbulent Flames ◽  
Laser Induced Incandescence

The local extinction and the nonlinear behaviors of a premixed methane/air flame under low-frequency acoustic excitation

2020 ◽  
Vol 34 (13) ◽  
pp. 2050138 ◽  
Author(s):  
Yongchao Sun ◽  
Mingbo Sun ◽  
Jiajian Zhu ◽  
Yang Xie ◽  
Hongbo Wang ◽  
...  
Keyword(s):  
High Speed ◽  
Excitation Frequency ◽  
Dominant Frequency ◽  
Local Extinction ◽  
Acoustic Excitation ◽  
Flame Extinction ◽  
Buoyant Force ◽  
Hot Gas ◽  
Nature Frequency ◽  
Production Zone

The local extinction and the nonlinear behavior of a premixed methane/air flame under acoustic excitation are investigated experimentally. High-speed photography and high-speed schlieren imaging are used to investigate the oscillation characteristics of the premixed methane/air flame. The flame structure shows a periodic fluctuation when the acoustic excitation is performed to the flame. The local flame extinction can be observed during the flame evolution process. During the local flame extinction process, the flame is found to be cut into two components, then the downstream one extinguishes shortly. The Particle Image Velocimetry (PIV) results suggest that the lower velocity at the separation point is one of the reasons for the flame local extinction. The flame without the acoustic excitation oscillates with a dominant frequency of 18 Hz, which is shown by the schlieren images to be related to the evolution of the hot gas around the flame driven by the buoyant force. When the acoustic excitation frequency is 100 Hz, the structure of the hot gas is destroyed, meanwhile the amplitude of the nature frequency decreases significantly. The hot gas structure appears regularly with the increasing excitation frequency. As a result, the amplitude of the nature frequency also increases gradually. Proper Orthogonal Decomposition (POD) analysis shows that the dominant frequency of the flame without the acoustic excitation is mainly caused by the evolution of the production zone of the flame and the fluctuation of the flame tip. The evolution of the production zone is driven by the buoyant force, which indicates that the result from POD method is consistent with the conclusion obtained from the high-speed schlieren images. Two dominant modes are obtained when the excitation frequencies are 100 and 200 Hz. The two modes are mainly caused by the process of the local flame extinction and the increasing flame length.

scholarly journals Large vapour cloud explosions, with particular reference to that at Buncefield

2012 ◽  
Vol 370 (1960) ◽  
pp. 544-566 ◽  
Author(s):  
D. Bradley ◽  
G. A. Chamberlain ◽  
D. D. Drysdale
Keyword(s):  
Land Use Planning ◽  
High Speed ◽  
Phase 1 ◽  
Turbulent Flames ◽  
Major Incident ◽  
Advisory Group ◽  
Storage Site ◽  
Two Phase ◽  
Underlying Mechanisms ◽  
The Uk

This paper first briefly surveys the energy releases in some major accidents. It then examines the analyses of the explosion at the Buncefield fuel storage site in the UK, one of the most intense accidental explosions in recent times. This followed the release of approximately 300 tonnes of winter-grade gasoline, when a 15 m high storage tank was overfilled for about 40 min before ignition of the resulting flammable mixture. The ensuing explosion was of a severity that had not been identified previously in a major hazard assessment of this type of facility. It was therefore imperative to investigate the event thoroughly and develop an understanding of the underlying mechanisms to inform future prevention, mitigation and land-use planning issues. The investigation of the incident was overseen by the Buncefield Major Incident Investigation Board. A separate Explosion Mechanism Advisory Group examined the evidence and reported on the severity of the explosion. It concluded that additional work was necessary and recommended that a two-stage project be initiated, phase 1 of which has been completed. The analyses of the damage and the derivation of explosion over-pressures are described. Possible explosion mechanisms and the evidence for them at Buncefield are discussed, in the light of other major incidents. Mechanisms that are reviewed include high-speed turbulent combustion, quasi-detonations, fully developed detonations, the generation of fireballs, flame instabilites, radiative heat transfer and aspects of two-phase burning. Of particular importance is the acceleration of turbulent flames along the line of trees and hedgerows. A number of conclusions are drawn and suggestions made for further research.

Propagation of Turbulent Natural Gas/Air Flames in Tubing With 90° Bends

2003 ◽  
Vol 125 (4) ◽  
pp. 304-310
Author(s):  
Michael D. Morgan ◽  
S. A. (Raj) Mehta ◽  
T. J. Al-Himyary ◽  
R. G. (Gord) Moore
Keyword(s):  
Natural Gas ◽  
High Speed ◽  
Small Diameter ◽  
Industrial Applications ◽  
Turbulent Flames ◽  
Process Equipment ◽  
Pressure Data ◽  
Flammable Gas ◽  
Internal Volume ◽  
Temperature Responses

Anytime flammable gas mixtures are handled, there is a risk of combustion. This is particularly true in many industrial applications where space is limited and equipment is located near sources of ignition. Unfortunately, there is a lack of understanding of combustion phenomena within process equipment such as mufflers, rotating blowout preventers, liquid traps, and dry gas seal assemblies. These vessels have small internal volumes, complex internal geometries, and are connected using small diameter piping. This paper discusses the results of a parametric study which was carried out to establish the nature of combustion within such vessels and tubing. The test vessel had an internal volume of 7 in3 (115 ml) and the tubing had a nominal diameter of 0.5 in (1.27 mm). Flowing, turbulent, pre-mixed natural gas/air mixtures were used. The study did not attempt to increase turbulence using devices such as mesh screens or attempt to stabilize the flame. The results from a representative sample of 76 tests, from the 5,000+ tests that have been completed, are discussed herein. Typical pressure and temperature responses are presented and analyzed. It is demonstrated that flames can be remotely detected using only high speed pressure data. Turbulent flames were formed whose velocity was found to be linearly dependant on Reynolds number.

Effect of an inhibitor on high-speed turbulent flames and the transition to detonation

Shock Waves ◽  
1996 ◽  
Vol 5 (5) ◽  
pp. 305-309
Author(s):  
M.H. Johnston ◽  
F. Zhang ◽  
D.L. Frost ◽  
J.H.S. Lee
Keyword(s):  
High Speed ◽  
Turbulent Flames ◽  
Transition To Detonation

Dynamics of Premixed H2/CH4 Flames Under Near-Blowoff Conditions

2009 ◽  
Author(s):  
Qingguo Zhang ◽  
Santosh J. Shanbhogue ◽  
Tim Lieuwen
Keyword(s):  
Strain Rate ◽  
Temporal Dynamics ◽  
Complex Dynamics ◽  
Vortex Breakdown ◽  
Local Strain ◽  
Mie Scattering ◽  
Flame Stabilization ◽  
Local Extinction ◽  
Extinction Events ◽  
Extinction Strain Rate

Swirling flows are widely used in industrial burners and gas turbine combustors for flame stabilization. Several prior studies have shown that these flames exhibit complex dynamics under near-blowoff conditions, associated with local flamelet extinction and alteration in the vortex breakdown flow structure. These extinction events are apparently due to the local strain rate irregularly oscillating above and below the extinction strain rate values near the attachment point. In this work, global, temporally resolved and detailed spatial measurements were obtained of hydrogen/methane flames. Supporting calculations of extinction strain rates were also performed using detailed kinetics. It is shown that flames become unsteady (or local extinctions happen) at a nearly constant extinction strain rate for different hydrogen/methane mixtures. Based upon analysis of these results, it is suggested that classic Damkohler number correlations of blowoff are, in fact, correlations for the onset of local-extinction events, not blowoff itself. Corresponding Mie scattering imaging of near-blowoff flames also was used to characterize the spatio-temporal dynamics of holes along the flame that are associated with local extinction.

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