Influence of Turbulent Scalar Mixing Physics on Premixed Flame Propagation

Kolla, Hemanth; Swaminathan, Nedunchezhian

doi:10.1155/2011/451351

Cited by 9 publications

(4 citation statements)

References 39 publications

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“…Thus, it seems that the modelling frame work used in this study is able to capture the flame liftoff heights of a range of conditions, dilution levels, jet velocities ranging from 12 to 30 m/s and 500 to 900 m/s in [46] for undiluted hydrogen, without having to change the combustion modelling parameters. The reason for such robust and consistently good behaviour of the combustion model is because of close coupling of the model parameters to the underlying important physical processes controlling the local burning rate as discussed in [46,[65][66][67][68].…”

Section: Influence Of Jet Velocity and Air-dilutionmentioning

confidence: 99%

Simulation of turbulent lifted methane jet flames: Effects of air-dilution and transient flame propagation

Chen

Ruan

Swaminathan

2015

Combustion and Flame

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Turbulent lifted methane jet flames with various air-dilution levels and a range of inlet velocities are simulated. A partially premixed combustion model based on premixed flamelets with presumed joint Probability Density Function (PDF) is used. The joint PDF is obtained using a copula to include the statistical correlation between mixture fraction, Z, and progress variable, c. The non-premixed combustion effect is included using a simple algebraic model. Both steady and unsteady RANS simulations are performed. The steady simulations show that the computed lift-off heights agree well with measured values for a wide range of jet velocities and air-dilution level. Both of the Z-c correlation and non-premixed combustion effects are found to be important to get the correct lift-off height. Their individual and combined effects are analysed systematically. The unsteady RANS results indicate that multi-stage flame development, namely the initial expansion, flame brush development, its propagation and final stabilisation, is captured reasonably well in simulations. The various stages of temporal evolution of the flame brush * Corresponding author.edge is captured well and the agreement with experimental measurements is good.

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Section: Influence Of Jet Velocity and Air-dilutionmentioning

confidence: 99%

Simulation of turbulent lifted methane jet flames: Effects of air-dilution and transient flame propagation

Chen

Ruan

Swaminathan

2015

Combustion and Flame

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“…It was suggested (Kobayashi et al, 1996) that the flame-angle measurements were likely to correspond most nearly to a Reynolds-averaged progress variable of C = 0.5, and based on earlier measurements (Smallwood et al, 1995), the turbulent-flame area at this value was estimated to be 1.2 to 1.5 times that at C = 0.05, this latter value having been suggested (Smallwood et al, 1995) to be a reasonable representation of the leading edge of the turbulent flame. Recent modeling efforts (Kolla et al, 2009(Kolla et al, , 2010Kolla and Swaminathan, 2011) have focused on the motion of this leading edge, which therefore would be a desirable value to select.…”

Section: Turbulent Burning Velocitiesmentioning

confidence: 99%

Structures of Methane-Air and Propane-Air Turbulent Premixed Bunsen Flames

Furukawa¹,

Yoshida²,

Williams

2016

Combustion Science and Technology

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Structures of turbulent Bunsen flames in the corrugated-flamelet regime were investigated by use of a three-color six-beam laser-Doppler velocimetry system. Four different mixtures with identical laminar burning velocities (0.34 m/s) were selected to facilitate comparisons-lean and rich methane, and lean and rich propane. A bimodal distribution, not previously reported in the literature on turbulent Bunsen flames, was observed in the radial component of gas velocity off-axis in the turbulent flame brush. Our previous measurements enabled the low-velocity mode to be identified as velocity fluctuations of the unburned mixture and the high-velocity mode as fluctuations of the burned-gas radial velocity. Favre-averaged and Reynolds-averaged reaction-progress variables were then calculated from these bimodal distributions, identifying an initially unexpected region near the flame tips where, at a fixed radius, the average progress variable decreased (rather than increasing) with increasing height over a short distance, likely through enhanced flamelet flapping, which has not been predicted by modeling but which appears to occur quite generally for sufficiently tall turbulent Bunsen flames in quiescent ambient environments, for the corrugated-flamelet regime. Conditioned and unconditioned Favre-average velocity components and intensities also were calculated from the data for future tests of modeling. The distributions of the progress variables also clearly showed that the turbulent burning velocity of the rich propane flame was appreciably larger than that of any of the other three, as was its radial flame-brush thickness at any given height, and its high-radial-velocity mode had a higher average velocity magnitude than the others. Similarly, the turbulent burning velocity and flame-brush thickness appear to be smaller for the lean propane flame. These differences can be attributed to influences of preferential oxygen diffusion to turbulence-induced flamelet bulges, not included in existing modeling approaches, for the rich propane flames, and to a corresponding inhibition of fuel diffusion to the bulges in the lean flames. The former phenomenon is related to but different from the wellknown cellular-flamelet instability, these effects occurring for flames that are stable to diffusive-thermal disturbances. It was concluded that a greater fraction of the total amount of heat release occurs in the upstream half of the turbulent flame brush in the rich propane flame, producing enhanced flow divergence in the upstream region, while the reduced ability of the slowly diffusing fuel to reach bulges in the lean flame generates the opposite effect. The results point to directions in which turbulent-combustion modeling needs to be improved, and an approach to modeling this type of preferential-diffusion effect is suggested.

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“…These parameters are specified to satisfy certain physical aspects of turbulence-flame interaction (Kolla et al, 2009;Kolla and Swaminathan, 2011) and so they cannot be changed arbitrarily. The Karlovitz number is defined as Ka u 0 =s 0…”

Section: Reaction Rate Modelmentioning

confidence: 99%

Simulation of Spherically Expanding Turbulent Premixed Flames

Ahmed

Swaminathan

2013

Combustion Science and Technology

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Statistically spherical expanding turbulent premixed flames are computed using an unsteady Reynolds-averaged Navier-Stokes (URANS) approach. Mean reaction rate is closed using strained and unstrained flamelet models and an algebraic model. The flamelets are parametrized using the scalar dissipation rate in the strained flamelet model. It is shown that this model is able to capture the measured growth rate of methane-air turbulent flame ball, which is free of thermo-diffusive instability. The spherical flames are observed to accelerate continuously. The flame brush thickness grows in time and the role of turbulent diffusion on this growth seems secondary compared to the convection due to the fluid velocity induced by the chemical reaction. The spherical flames have larger turbulent flame speed, the leading-edge displacement speed s t , compared to the planar flames for a given turbulence and thermochemical condition. The computational results suggest s t =s 0 L $ Re n t with 0.57 n 0.58, where Re t is the turbulence Reynolds number and s 0 L is the unstrained planar laminar flame speed, for both spherical and planar flames.

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Influence of Turbulent Scalar Mixing Physics on Premixed Flame Propagation

Cited by 9 publications

References 39 publications

Simulation of turbulent lifted methane jet flames: Effects of air-dilution and transient flame propagation

Simulation of turbulent lifted methane jet flames: Effects of air-dilution and transient flame propagation

Structures of Methane-Air and Propane-Air Turbulent Premixed Bunsen Flames

Simulation of Spherically Expanding Turbulent Premixed Flames

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