scholarly journals Burning Rate in Impinging Jet Flames

2011 ◽  
Vol 2011 ◽  
pp. 1-11 ◽  
Author(s):  
A. N. Lipatnikov
Keyword(s):  
Turbulent Combustion ◽  
Burning Velocity ◽  
Impinging Jet ◽  
Turbulent Flames ◽  
Research Groups ◽  
Scalar Flux ◽  
Premixed Turbulent Combustion ◽  
Progress Variable ◽  
Premixed Turbulent Flames ◽  
The Mean

A method for evaluating burning velocity in premixed turbulent flames stabilized in divergent mean flows is quantitatively validated using numerical approximations of measured axial profiles of the mean combustion progress variable, mean and conditioned axial velocities, and axial turbulent scalar flux, obtained by four research groups from seven different flames each stabilized in an impinging jet. The method is further substantiated by analyzing the combustion progress variable balance equation that is yielded by the extended Zimont model of premixed turbulent combustion. The consistency of the model with the aforementioned experimental data is also demonstrated.

A spectral closure for premixed turbulent combustion in the flamelet regime

1992 ◽  
Vol 242 ◽  
pp. 611-629 ◽  
Author(s):  
N. Peters
Keyword(s):  
Field Equation ◽  
Scalar Field ◽  
Dimensional Analysis ◽  
Turbulent Combustion ◽  
Burning Velocity ◽  
Turbulent Flames ◽  
Scalar Dissipation ◽  
Premixed Turbulent Combustion ◽  
Flame Stretch ◽  
The Mean

Premixed turbulent combustion in the flamelet regime is analysed on the basis of a field equation. This equation describes the instantaneous flame contour as an isoscalar surface of the scalar field G(x,t). The field equation contains the laminar burning velocity sL as velocity scale and its extension includes the effect of flame stretch involving the Markstein length [Lscr ] as a characteristic lengthscale of the order of the flame thickness. The scalar G(x,t) plays a similar role for premixed flamelet combustion as the mixture fraction Z(x,t) in the theory of non-premixed flamelet combustion.Equations for the mean $\overline{G}$ and variance $\overline{G^{\prime 2}}$ are derived. Additional closure problems arise for the mean source terms in these equations. In order to understand the nature of these terms an ensemble of premixed flamelets with arbitrary initial conditions in constant-density homogeneous isotropic turbulence is considered. An equation for the two-point correlation $\overline{G^{\prime}({\boldmath x},t)G^{\prime}({\boldmath x}+{\boldmath r},t)}$ is derived. When this equation is transformed into spectral space, closure approximations based on the assumption of locality and on dimensional analysis are introduced. This leads to a linear equation for the scalar spectrum function Γ(k,t), which can be solved analytically. The solution Γ(k,t) is analysed by assuming a small-wavenumber cutoff at k0 = lT−1, where lT is the integral lengthscale of turbulence. There exists a $k^{-\frac{5}{3}}$ spectrum between lT and LG, where LG is the Gibson scale. At this scale turbulent fluctuations of the scalar field G(x,t) are kinematically restored by the smoothing effect of laminar flame propagation. A quantity called kinematic restoration ω is introduced, which plays a role similar to the scalar dissipation χ for diffusive scalars.By calculating the appropriate moments of Γ(k,t), an algebraic relation between ω, $\omega,\overline{G^{\prime}({\boldmath x},t)^2}$, the integral lengthscale lT and the viscous dissipation ε is derived. Furthermore, the scalar dissipation χ[Lscr ], based on the Markstein diffusivity [Dscr ][Lscr ] = sL [Lscr ], and the scalar-strain co-variance Σ[Lscr ] are related to ω. Dimensional analysis, again, leads to a closure of the main source term in the equation for the mean scalar $\overline{G}$. For the case of plane normal and oblique turbulent flames the turbulent burning velocity sT and the flame shape is calculated. In the absence of flame stretch the linear relation sT ∼ u′ is recovered. The flame brush thickness is of the order of the integral lengthscale. In the case of a V-shaped flame its increase with downstream position is calculated.

scholarly journals Comparison of Presumed PDF Models of Turbulent Flames

2012 ◽  
Vol 2012 ◽  
pp. 1-15 ◽  
Author(s):  
Chen Huang ◽  
Andrei N. Lipatnikov
Keyword(s):  
Heat Release ◽  
Burning Velocity ◽  
Mixture Fraction ◽  
Beta Function ◽  
Reaction Rates ◽  
Turbulent Flames ◽  
Implicit Assumption ◽  
Dirac Delta ◽  
Progress Variable ◽  
The Mean

Over the past years, the use of a presumed probability density function (PDF) for combustion progress variable or/and mixture fraction has been becoming more and more popular approach to average reaction rates in premixed and partially premixed turbulent flames. Commonly invoked for this purpose is a beta-function PDF or a combination of Dirac delta functions, with the parameters of the two PDFs being determined based on the values of their first and second moments computed by integrating proper balance equations. Because the choice of any of the above PDFs appears to be totally arbitrary as far as underlying physics of turbulent combustion is concerned, the use of such PDFs implies weak sensitivity of the key averaged quantities to the PDF shape. The present work is aimed at testing this implicit assumption by comparing mean heat release rates, burning velocities, and so forth, averaged by invoking the aforementioned PDFs, with all other things being equal. Results calculated in the premixed case show substantial sensitivity of the mean heat release rate to the shape of presumed combustion-progress-variable PDF, thus, putting the approach into question. To the contrary, the use of a presumed mixture-fraction PDF appears to be a sufficiently reasonable simplification for modeling the influence of fluctuations in the mixture fraction on the mean burning velocity provided that the mixture composition varies within flammability limits.

scholarly journals A balance equation for the mean rate of product creation in premixed turbulent flames

2017 ◽  
Vol 36 (2) ◽  
pp. 1893-1901 ◽  
Author(s):  
Vladimir A. Sabelnikov ◽  
Andrei N. Lipatnikov ◽  
Nilanjan Chakraborty ◽  
Shinnosuke Nishiki ◽  
Tatsuya Hasegawa
Keyword(s):  
Balance Equation ◽  
Turbulent Flames ◽  
Premixed Turbulent Flames ◽  
The Mean ◽  
Product Creation

scholarly journals Effect of Stretch on Local Burning Velocity of Premixed Turbulent Flames

2007 ◽  
Vol 2 (2) ◽  
pp. 268-280 ◽  
Author(s):  
Masaya NAKAHARA ◽  
Hiroyuki KIDO ◽  
Takamori SHIRASUNA ◽  
Koichi HIRATA
Keyword(s):  
Burning Velocity ◽  
Turbulent Flames ◽  
Premixed Turbulent Flames ◽  
Local Burning

Numerical Modeling of Stationary But Developing Premixed Turbulent Flames

2006 ◽  
Author(s):  
Pratap Sathiah ◽  
Andrei N. Lipatnikov
Keyword(s):  
Bluff Body ◽  
Burning Velocity ◽  
Rectangular Channel ◽  
Turbulent Flame ◽  
Flame Stabilization ◽  
Turbulent Flames ◽  
Turbulent Diffusivity ◽  
Flame Thickness ◽  
Premixed Turbulent Flames ◽  
Premixed Turbulent Flame

A typical stationary premixed turbulent flame is the developing flame, as indicated by the growth of mean flame thickness with distance from flame-stabilization point. The goal of this work is to assess the importance of modeling flame development for RANS simulations of confined stationary premixed turbulent flames. For this purpose, submodels for developing turbulent diffusivity and developing turbulent burning velocity, which were early suggested by our group (FSC model) and validated for expanding spherical flames [4], have been incorporated into the so-called Zimont model of premixed turbulent combustion and have been implemented into the CFD package Fluent 6.2. The code has been run to simulate a stationary premixed turbulent flame stabilized behind a triangular bluff body in a rectangular channel using both the original and extended models. Results of these simulations show that the mean temperature and velocity fields in the flame are markedly affected by the development of turbulent diffusivity and burning velocity.

412 Influence of Markstein Number on Local Burning Velocity of Premixed Turbulent Flames

2005 ◽  
Vol 2005.58 (0) ◽  
pp. 145-146
Author(s):  
Masaya NAKAHARA ◽  
Hiroyuki KIDO ◽  
Kenshiro NAKASHIMA ◽  
Hideaki TAKAMOTO ◽  
Koichi HIRATA
Keyword(s):  
Burning Velocity ◽  
Turbulent Flames ◽  
Premixed Turbulent Flames ◽  
Markstein Number ◽  
Local Burning
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