Examination of probability distribution of mixture fraction in LES/FDF modelling of a turbulent partially premixed jet flame

2021 ◽  
pp. 1-18
Author(s):  
Haifeng Wang ◽  
Pei Zhang ◽  
Jie Tao
Keyword(s):  
Probability Distribution ◽  
Mixture Fraction ◽  
Jet Flame ◽  
Partially Premixed

Steady-State Simulation of a Methane-Air Partially Premixed Turbulent Flame

2001 ◽  
Author(s):  
Graham Goldin ◽  
Dipankar Choudhury
Keyword(s):  
Steady State ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Equilibrium Mixture ◽  
Flamelet Model ◽  
Jet Flame ◽  
Partially Premixed ◽  
Partially Premixed Flame ◽  
Steady State Simulation ◽  
Laminar Flamelet

Abstract Two steady-state simulations of a benchmark (Sandia Flame D) methane-air, turbulent, partially premixed flame are compared. The first uses an equilibrium mixture fraction model for the thermo-chemistry, while the second uses a steady, strained laminar-flamelet model. These non-premixed combustion models are coupled with a premixed reaction progress model to simulate a partially premixed jet flame. The laminar-flamelet approach predicts CO and H2 more accurately than the equilibrium model by accounting for the unbumt premixed stream within individual flamelets, and improved radical (such as OH) predictions by incorporating non-equilibrium chemistry effects due aerodynamic strain (fluid shear).

scholarly journals Observations on Jet-Flame Blowout

2008 ◽  
Vol 2008 ◽  
pp. 1-7 ◽  
Author(s):  
N. J. Moore ◽  
J. L. McCraw ◽  
K. M. Lyons
Keyword(s):  
Reaction Zone ◽  
Mixture Fraction ◽  
Flame Structure ◽  
Leading Edge ◽  
Transient Behavior ◽  
Turbulent Flames ◽  
Ignition Source ◽  
Jet Flame ◽  
Physically Based ◽  
Air Diffusion

The mechanisms that cause jet-flame blowout, particularly in the presence of air coflow, are not completely understood. This work examines the role of fuel velocity and air coflow in the blowout phenomenon by examining the transient behavior of the reaction zoneat blowout. The results of video imaging of a lifted methane-air diffusion flame at near blowout conditions are presented. Two types of experiments are described. In the first investigation, a flame is established and stabilized at a known, predetermined downstream location with a constant coflow velocity, and then the fuel velocity is subsequently increased to cause blowout. In the other, an ignition source is used to maintain flame burning near blowout and the subsequent transient behavior to blowout upon removal of the ignition source is characterized. Data from both types of experiments are collected at various coflow and jet velocities. Images are used to ascertain the changes in the leading edge of the reaction zone prior to flame extinction that help to develop a physically-based model to describe jet-flame blowout. The data report that a consistent predictor of blowout is the prior disappearance of the axially oriented flame branch. This is witnessed despite a turbulent flames' inherent variable behavior. Interpretations are also made in the light of analytical mixture fraction expressions from the literature that support the notion that flame blowout occurs when the leading edge reaches the vicinity of the lean-limit contour, which coincides approximately with the conditions for loss of the axially oriented flame structure.

scholarly journals A priori investigation of subgrid correlation of mixture fraction and progress variable in partially premixed flames

2018 ◽  
Vol 22 (5) ◽  
pp. 862-882 ◽  
Author(s):  
Zhi X. Chen ◽  
N. Anh Khoa Doan ◽  
Shaohong Ruan ◽  
Ivan Langella ◽  
N. Swaminathan
Keyword(s):  
Mixture Fraction ◽  
A Priori ◽  
Premixed Flames ◽  
Progress Variable ◽  
Partially Premixed Flames ◽  
Partially Premixed

The Application of Flamelet-Generated Manifold in the Modeling of Stratified Premixed Cooled Flames

2014 ◽  
Author(s):  
Andrea Donini ◽  
Robert J. M. Bastiaans ◽  
Jeroen A. van Oijen ◽  
L. Philip H. de Goey
Keyword(s):  
Heat Loss ◽  
Mixture Fraction ◽  
Control Variable ◽  
Full Detail ◽  
Detailed Chemistry ◽  
Air Inlet ◽  
Flamelet Generated Manifold ◽  
Partially Premixed ◽  
Cost Efficient ◽  
Combustion Processes

CFD predictions of flame position, stability and emissions are essential in order to obtain optimized combustor designs in a cost efficient way. However, the numerical modeling of practical combustion systems is a very challenging task. As a matter of fact, the use of detailed reaction mechanisms is necessary for such reliable predictions. Unfortunately, the modeling of the full detail of practical combustion equipment is currently prohibited by the limitations in computing power, given the large number of species and reactions involved. The Flamelet-Generated Manifold (FGM) method reduces these computational costs by several orders of magnitude without loosing too much accuracy. Hereby FGM enables the application of reliable chemistry mechanisms in CFD simulations of combustion processes. In the present paper a computational analysis of partially premixed non-adiabatic flames is presented. In this scope, chemistry is reduced by the use of the FGM method. In the FGM technique the progress of the flame is generally described by a few control variables. For each control variable a transport equation is solved during run-time. The flamelet system is computed in a pre-processing stage, and a manifold with all the information about combustion is stored in a tabulated form. This research applies the FGM chemistry reduction method to describe partially premixed flames in combination with heat loss, which is a relevant condition for stationary gas turbine combustors. In order to take this into account, in the present implementation the reaction evolution is described by the reaction progress variable, the heat loss is described by the enthalpy and the local equivalence ratio effect on the reaction is represented by the mixture fraction. A series of test simulations is performed for a two dimensional geometry, characterized by a distinctive stratified methane/air inlet, and compared with detailed chemistry simulations. The results indicate that detailed simulations are reproduced in an excellent way with FGM.

scholarly journals Mechanisms of flame stabilisation at low lifted height in a turbulent lifted slot-jet flame

2015 ◽  
Vol 777 ◽  
pp. 633-689 ◽  
Author(s):  
Shahram Karami ◽  
Evatt R. Hawkes ◽  
Mohsen Talei ◽  
Jacqueline H. Chen
Keyword(s):  
Flame Propagation ◽  
Mixture Fraction ◽  
Turbulent Transport ◽  
Experimental Studies ◽  
Leading Edge ◽  
Basic Structure ◽  
Plane Motion ◽  
Flame Propagation Velocity ◽  
Jet Flame ◽  
The Rich

A turbulent lifted slot-jet flame is studied using direct numerical simulation (DNS). A one-step chemistry model is employed with a mixture-fraction-dependent activation energy which can reproduce qualitatively the dependence of the laminar burning rate on the equivalence ratio that is typical of hydrocarbon fuels. The basic structure of the flame base is first examined and discussed in the context of earlier experimental studies of lifted flames. Several features previously observed in experiments are noted and clarified. Some other unobserved features are also noted. Comparison with previous DNS modelling of hydrogen flames reveals significant structural differences. The statistics of flow and relative edge-flame propagation velocity components conditioned on the leading edge locations are then examined. The results show that, on average, the streamwise flame propagation and streamwise flow balance, thus demonstrating that edge-flame propagation is the basic stabilisation mechanism. Fluctuations of the edge locations and net edge velocities are, however, significant. It is demonstrated that the edges tend to move in an essentially two-dimensional (2D) elliptical pattern (laterally outwards towards the oxidiser, then upstream, then inwards towards the fuel, then downstream again). It is proposed that this is due to the passage of large eddies, as outlined in Su et al. (Combust. Flame, vol. 144 (3), 2006, pp. 494–512). However, the mechanism is not entirely 2D, and out-of-plane motion is needed to explain how flames escape the high-velocity inner region of the jet. Finally, the time-averaged structure is examined. A budget of terms in the transport equation for the product mass fraction is used to understand the stabilisation from a time-averaged perspective. The result of this analysis is found to be consistent with the instantaneous perspective. The budget reveals a fundamentally 2D structure, involving transport in both the streamwise and transverse directions, as opposed to possible mechanisms involving a dominance of either one direction of transport. It features upstream transport balanced by entrainment into richer conditions, while on the rich side, upstream turbulent transport and entrainment from leaner conditions balance the streamwise convection.

Mixture fraction imaging in a lifted methane jet flame

1996 ◽  
Vol 107 (3) ◽  
pp. 307-313 ◽  
Author(s):  
S.H. Stårner ◽  
R.W. Bilger ◽  
J.H. Frank ◽  
D.F. Marran ◽  
M.B. Long
Keyword(s):  
Mixture Fraction ◽  
Jet Flame

Simulation of Turbulent Lifted Flames Using a Partially-Premixed Coherent Flame Model (PCFM)

2008 ◽  
Author(s):  
Yongzhe Zhang ◽  
Rajesh Rawat
Keyword(s):  
Turbulent Combustion ◽  
Practical Interest ◽  
Flame Stabilization ◽  
Premixed Combustion ◽  
Pollutant Emissions ◽  
Jet Flame ◽  
Premixed Turbulent Combustion ◽  
Partially Premixed Combustion ◽  
Lifted Flames ◽  
Partially Premixed

Partially-premixed combustion occurs in many combustion devices of practical interest, such as gas-turbine combustors. Development of corresponding turbulent combustion models is important to improve the design of these systems in efforts to reduce fuel consumption and pollutant emissions. Turbulent lifted flames have been a canonical problem for testing models designed for partially-premixed turbulent combustion. In this paper we propose modifications to the coherent flame model (CFM) so that it can be brought to the simulation of partially-premixed combustion. For the primary premixed flame, a transport equation for flame area density is solved in which the wrinkling effects of the flame stretch and flame annihilation are considered. For the subsequent non-premixed zone, a laminar flamelet PPDF methodology, which accounts for the non-equilibrium and finiterate chemistry effects, is adopted. The model is validated against the experimental data on a lifted H2/N2 jet flame issuing into a vitiated coflow. In general there is fairly good agreement between the calculations and measurements both in profile shapes and peak values. Based on the simulation results the flame stabilization mechanism for lifted flames is investigated.

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