Images of the two-dimensional field and temperature gradients to quantify mixing rates within a non-premixed turbulent jet flame

Everest, D. A.; Driscoll, James F.; Dahm, Werner J. A.; Feikema, Douglas A.

doi:10.1016/0010-2180(94)00193-v

Cited by 42 publications

(21 citation statements)

References 17 publications

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“…The two-dimensional temperature distribution obtained is related to the scalar dissipation rate χ through the thermal dissipation rate χ T under the assumptions of a Lewis number of unity and temperature being a function of only mixture fraction (16) . Here, the differential diffusion effect attributable to the mixed fuel of methane and hydrogen is ignored due to short residence time of the fuel determined on the basis of liftoff height for the present cases, being evaluated as approximately t res = 6.6 × 10 −4 s. Since the diffusion coefficients of methane and hydrogen to air are D CH 4 = 0.229 cm 2 /s and D H 2 = 0.787 cm 2 /s in cold flow, respectively, the difference between the characteristic diffusion distances ∆l is evaluated on the basis of (Dt res ) 1/2 as approximately 0.1 mm, being comparable to the present pixel spacing.…”

Section: Evaluation Of Scalar Dissipation Ratementioning

confidence: 99%

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Nonpremixed Flamelet Statistics at Flame Base of Lifted Turbulent Jet Nonpremixed Flames

Noda

Mori

Hongo

et al. 2005

JSME international journal. Ser. B, Fluids and thermal engineer

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Nonpremixed flamelet statistics at the flame base of lifted turbulent nonpremixed flames are investigated experimentally using a planar temperature Rayleigh scattering method. A methane/hydrogen mixture is supplied from a tube of 3.2 mm I.D. into the surrounding air flow so as to form two lifted turbulent nonpremixed flames having exit velocities of 50 m/s (Re = 4 200) and 80 m/s (Re = 6 700), respectively. Temperature data are related to maximum temperature at several flame positions based on the instantaneous flame base tip as containing information on the reaction region of each nonpremixed flamelet at each position. The statistics in terms of maximum temperature, thermal dissipation rate, scalar dissipation rate, and flame brush are discussed with reference to the modeling of the flame base structure. The scalar dissipation rate has log-normal statistics and the quenching scalar dissipation rate is lower than the critical value predicted using the uniformly strained counter nonpremixed flame. These statistics are compared to those obtained using a model proposed by Müller et al.(1) , which combines the flamelet model and the scalar field variable to predict lifted turbulent nonpremixed flames. The comparison has shown that the model can qualitatively predict lifted turbulent nonpremixed flames, but modification is required in order to obtain more accurate quantitative prediction taking into account the edge flame structure, the statistics of scalar dissipation rate, and the statistics of flame brush.

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Section: Evaluation Of Scalar Dissipation Ratementioning

confidence: 99%

“…Thus, the scalar dissipation rate is re-expressed as a function of thermal dissipation rate and temperature gradient with respect to the mixture fraction as (16) …”

Section: Evaluation Of Scalar Dissipation Ratementioning

confidence: 99%

Nonpremixed Flamelet Statistics at Flame Base of Lifted Turbulent Jet Nonpremixed Flames

Noda

Mori

Hongo

et al. 2005

JSME international journal. Ser. B, Fluids and thermal engineer

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“…Furthermore, two other trends are distinctly noticeable: 1) the increase in 8 CH with axial location for all flames and 2) the increase in 5 CH due to increased jet velocity. The former can be attributed to the decrease in scalar dissipation from base to tip [33][34][35][36]; in conjunction with the conversion from a top-hat to Gaussian profile, local gradients must decrease as well, thereby widening any isocontour of mixture fraction. However, the increase in 8 CH with jet-exit velocity is not predicted by flamelet theory.…”

Section: Reaction Zone Structure and Thicknessmentioning

confidence: 99%

Simultaneous CH planar laser-induced fluorescence and particle imaging velocimetry in turbulent nonpremixed flames

Carter

Donbar

Driscoll

1998

Applied Physics B: Lasers and Optics

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The present work addresses the question of whether the chemical reaction zone within a turbulent, high-Reynolds-number jet flame is thin-and can be modeled using strained wrinkled laminar flamelet theory-or is thick-and must be modeled using distributed reaction zone theory. The region near the wrinkled instantaneous stoichiometric contour is identified using CH Planar Laser-Induced Fluorescence (PLIF) imaging and the strain on this interface is measured using simultaneous Particle Imaging Velocimetry (PIV) diagnostics. With a separate set of simultaneous images, the relative position of the CH and OH radicals is observed using PLIF. It is found that the CH reaction zone remains thin and rarely exceeds 1 mm, even near the flame tip in a high-Reynolds-number (18,600) jet flame. The mean thickness of the CH reaction layer (5 C H) increases from 0.3 to 0.8 mm in the streamwise direction; this is expected because the scalar dissipation rate is known to decrease with downstream distance and should cause a corresponding increase in 8 CH . However, 8 CH also increases with jet velocity, which is not predicted by theory. Furthermore, the mean strain rates on the stoichiometric contour increase in the streamwise direction, which is contrary to previous predictions. Thus, strain rate does not, in general, scale with the local dissipation rate in a turbulent flame, and this aspect of the counterflow flow analogy is not valid. It is concluded that unsteady laminar flamelet concepts are consistent with most of the present observations, but a method independent of the local dissipation rate is needed to predict the local strain rate. IntroductionOften, the analogy is made between segments of turbulent nonpremixed jet flames and a steady laminar counterflow diffusion flame that is selected to have the same strain rate as the turbulent flame segment; particularly, this analogy is used in "laminar flamelet models" [1,2]. The flamelet regime, by definition, exists over regions in which the flame front is thinner than the smallest scale of turbulence, and thus the flame front can be modeled as an ensemble of laminar flamelets. For the flamelet analogy to be realistic, several factors must be known: 1. if the reaction layers are sufficiently thin (rather than thick, distributed zones); 2. if the reaction-layer properties (e.g. radical concentrations, thickness) scale as predicted by counterflow theory; 3. how frequently the layers extinguish or merge; and 4. if the strain on the turbulent reaction layers is proportional to the dissipation rate as in counterflow flames [2]. If all of these conditions are satisfied, it becomes possible to apply several promising modeling ideas which draw heavily on flamelet theory, including the original flamelet model [2], the Local Integral Moment (LIM) model [3,4], the Large Eddy Simulation (LES) model [5], and Direct Numerical Simulation (DNS) [6]. To date, lack of information on the structure of turbulent

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“…乱流拡散火炎の局所構造を決定づけるパラメーターとして，スカラー散逸率 χ や混合分率 Z などがある．ルイス数 Le を 1 としたとき， χ は χ T に比例することから (2) ，Le=1 の仮定を導入することによって，乱流拡散火炎中の温度データから得られる χ T を用いて，乱流火炎中の χ を評価した研究がある (6), (7) ．一方，乱流拡散火炎中の各種濃度および温度分布をレーザー計測し，その計測結果から直接 χ を求める研究も行われている …”

Section: 緒言unclassified

“…の結果は，x/d=42，r/d=0.08-0.14 の範囲において，確率密度関数が最大となる χ T の平均値を示している．野田ら (6) の結果は，x/d=10-15，r/d=1-5 の範囲において，確率密度関数が最大となる χ T の範囲を示している．Wang らの結果 Present work Everest et al (2) Noda et al (6) Wang et al …”

Section: ・3 空気・燃料吹出し速度が温度勾配と温度消散率の最大値に及ぼす影響unclassified

Thermal and Scalar Dissipation Rates of Stretched Cylindrical Diffusion Flame

Suenaga

Yanaoka

Kitano³

et al. 2013

Trans.JSME, B

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Structures of stretched cylindrical diffusion flame with large curvature were investigated experimentally.Temperature distributions of fuel-diluent mixture/air flames were measured. Fuel was diluted with diluent gases (N 2 , Ar and He) in order to set the Lewis number Le~1. Fuel (Air) was supplied from inside (outside) of the cylindrical flame.Thermal dissipation rates were calculated from measured temperature distribution. In the case of Le=1, the scalar dissipation rate is proportional to the thermal dissipation rate. Therefore, the stoichiometric scalar dissipation rate was evaluated using the maximum value of the thermal dissipation rates obtained from each temperature distribution.Generally, it is known that the scalar dissipation rate of the counterflow flat diffusion flame increases as the flame stretch rate increases. However, in the case of the cylindrical diffusion flames, the scalar dissipation rate has a maximum value or decreases with the stretch rate.

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Images of the two-dimensional field and temperature gradients to quantify mixing rates within a non-premixed turbulent jet flame

Cited by 42 publications

References 17 publications

Nonpremixed Flamelet Statistics at Flame Base of Lifted Turbulent Jet Nonpremixed Flames

Nonpremixed Flamelet Statistics at Flame Base of Lifted Turbulent Jet Nonpremixed Flames

Simultaneous CH planar laser-induced fluorescence and particle imaging velocimetry in turbulent nonpremixed flames

Thermal and Scalar Dissipation Rates of Stretched Cylindrical Diffusion Flame

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