The Modelling and Measurement of Local Flame Surface Orientation inTurbulent Premixed Flames

1998 ◽  
Vol 137 (1-6) ◽  
pp. 347-358 ◽  
Author(s):  
Y. ZHANG ◽  
K. N. C. BRAY ◽  
B. ROGG
Keyword(s):  
Premixed Flames ◽  
Surface Orientation ◽  
Flame Surface

scholarly journals Modelling of Conditional Scalar Dissipation Rate in Turbulent Premixed Combustion

Computation ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 26 ◽  
Author(s):  
Shokri Amzin ◽  
Mariusz Domagała
Keyword(s):  
Dissipation Rate ◽  
Premixed Flames ◽  
Moment Closure ◽  
Navier Stokes ◽  
Scalar Dissipation ◽  
Flame Surface ◽  
Scalar Dissipation Rate ◽  
Turbulent Premixed Flames ◽  
Conditional Moment ◽  
Turbulent Premixed

In turbulent premixed flames, for the mixing at a molecular level of reactants and products on the flame surface, it is crucial to sustain the combustion. This mixing phenomenon is featured by the scalar dissipation rate, which may be broadly defined as the rate of micro-mixing at small scales. This term, which appears in many turbulent combustion methods, includes the Conditional Moment Closure (CMC) and the Probability Density Function (PDF), requires an accurate model. In this study, a mathematical closure for the conditional mean scalar dissipation rate, <Nc|ζ>, in Reynolds, Averaged Navier–Stokes (RANS) context is proposed and tested against two different Direct Numerical Simulation (DNS) databases having different thermochemical and turbulence conditions. These databases consist of lean turbulent premixed V-flames of the CH4-air mixture and stoichiometric turbulent premixed flames of H2-air. The mathematical model has successfully predicted the peak and the typical profile of <Nc|ζ> with the sample space ζ and its prediction was consistent with an earlier study.

Flame surface statistics of constant-pressure turbulent expanding premixed flames

2014 ◽  
Vol 26 (4) ◽  
pp. 045109 ◽  
Author(s):  
Abhishek Saha ◽  
Swetaprovo Chaudhuri ◽  
Chung K. Law
Keyword(s):  
Constant Pressure ◽  
Premixed Flames ◽  
Flame Surface ◽  
Surface Statistics

scholarly journals An analytical model based on the G-equation for the response of technically premixed flames to perturbations of equivalence ratio

2017 ◽  
Vol 10 (2) ◽  
pp. 103-110 ◽  
Author(s):  
Alp Albayrak ◽  
Wolfgang Polifke
Keyword(s):  
Impulse Response ◽  
Time Scale ◽  
Equivalence Ratio ◽  
Premixed Flames ◽  
Flame Speed ◽  
Flame Surface ◽  
Heat Of Reaction ◽  
Local Behavior ◽  
Model Based ◽  
Flame Shape

A model for the response of technically premixed flames to equivalence ratio perturbations is proposed. The formulation, which is an extension of an analytical flame tracking model based on the linearized G-equation, considers the flame impulse response to a local, impulsive, infinitesimal perturbation that is transported by convection from the flame base towards the flame surface. It is shown that the contributions of laminar flame speed and heat of reaction to the impulse response exhibit a local behavior, i.e. the flame responds at the moment when and at the location where the equivalence ratio perturbation reaches the flame surface. The time lag of this process is related to a convective time scale, which corresponds to the convective transport of fuel from the base of the flame to the flame surface. On the contrary, the flame surface area contribution exhibits a non-local behavior: albeit fluctuations of the flame shape are generated locally due to a distortion of the kinematic balance between flame speed and the flow velocity, the resulting wrinkles in flame shape are then transported by convection towards the flame tip with the restorative time scale. The impact of radial non-uniformity in equivalence ratio perturbations on the flame impulse response is demonstrated by comparing the impulse responses for uniform and parabolic radial profiles. Considerable deviation in the phase of the flame transfer function, which is important for thermo-acoustic stability, is observed.

scholarly journals Flame surface density based modelling of head-on quenching of turbulent premixed flames

2017 ◽  
Vol 36 (2) ◽  
pp. 1817-1825 ◽  
Author(s):  
Johannes Sellmann ◽  
Jiawei Lai ◽  
Andreas M Kempf ◽  
Nilanjan Chakraborty
Keyword(s):  
Surface Density ◽  
Premixed Flames ◽  
Flame Surface ◽  
Turbulent Premixed Flames ◽  
Flame Surface Density ◽  
Turbulent Premixed

scholarly journals Effects of Lewis Number on the Evolution of Curvature in Spherically Expanding Turbulent Premixed Flames

Fluids ◽  
2019 ◽  
Vol 4 (1) ◽  
pp. 12 ◽  
Author(s):  
Ahmad Alqallaf ◽  
Markus Klein ◽  
Nilanjan Chakraborty
Keyword(s):  
Transport Equation ◽  
Burning Rate ◽  
Flame Propagation ◽  
Premixed Flames ◽  
Lewis Number ◽  
Flame Surface ◽  
Turbulent Premixed Flames ◽  
Diffusive Instability ◽  
Negatively Curved ◽  
Positively Curved

The effects of Lewis number on the physical mechanisms pertinent to the curvature evolution have been investigated using three-dimensional Direct Numerical Simulation (DNS) of spherically expanding turbulent premixed flames with characteristic Lewis number of L e = 0.8 , 1.0 and 1.2. It has been found that the overall burning rate and the extent of flame wrinkling increase with decreasing Lewis number L e , and this tendency is particularly prevalent for the sub-unity Lewis number (e.g., L e = 0.8 ) case due to the occurrence of the thermo-diffusive instability. Accordingly, the L e = 0.8 case has been found to exhibit higher probability of finding saddle topologies with large magnitude negative curvatures in comparison to the corresponding L e = 1.0 and 1.2 cases. It has been found that the terms in the curvature transport equation due to normal strain rate gradients and curl of vorticity arising from both fluid flow and flame normal propagation play pivotal roles in the curvature evolution in all cases considered here. The net contribution of the source/sink terms of the curvature transport equation tends to increase the concavity and convexity of the flame surface in the negatively and positively curved locations, respectively for the L e = 0.8 case. This along with the occurrence of high and low temperature (and burning rate) values at the positively and negatively curved zones, respectively acts to augment positive and negative curved wrinkles induced by turbulence in the L e = 0.8 case, which is indicative of thermo-diffusive instability. By contrast, flame propagation effects tend to weakly promote the concavity of the negatively curved cusps, and act to decrease the convexity of the highly positively curved bulges in the L e = 1.0 and 1.2 cases, which are eventually smoothed out due to high and low values of displacement speed S d at negatively and positively curved locations, respectively. Thus, flame propagation tends to smoothen the flame surface in the L e = 1.0 and 1.2 cases.

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