A Hybrid Flamelet Generated Manifold Model for Modeling Partially Premixed Turbulent Combustion Flames

2017 ◽  
Author(s):  
Rakesh Yadav ◽  
Ashoke De ◽  
Sandeep Jain
Keyword(s):  
Hybrid Model ◽  
Laminar Flame ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Hybrid Approach ◽  
Smooth Transition ◽  
Flamelet Generated Manifold ◽  
Partially Premixed ◽  
Lift Off ◽  
And Diffusion

In this work, a hybrid Flamelet Generated Manifold (FGM) method has been implemented in which both premixed and diffusion based laminar flame manifolds are generated independently and used within one solution framework to capture the multiple combustion regimes inside a combustor. The two manifolds are generated by solving the conservation of species and energy in a transformed space of mixture fraction and progress variable. The mixture averaged properties in a combustor are then calculated using a scalar weighted contribution of premixed and diffusion manifolds. This scalar represents the extent of premixing inside the combustor and its normalized value is obtained from a scalar product of the mean gradients of fuel and oxidizer mass fractions. A volume-weighted smoothing is performed on this normalized scalar to ensure smooth transition between the premixed to diffusion regimes and vice-versa, from one location to another location inside the combustor. This hybrid or multi-regime FGM approach is validated for two turbulent CH4-air partially premixed flames. The first flame chosen in the current work is a lifted turbulent flame, while the second flame is pilot-stabilized flame. First, the computations are performed for premixed- and diffusion-based laminar manifolds and then the results with hybrid models are presented. The results of the hybrid approach are compared for predicting the lift-off height, which is driven by the balance of turbulence and kinetics at any location. It is observed that the hybrid model leads to an improvement in the prediction of the lift-off height prediction. The new hybrid model is a generic representation of the FGM modeling, which enables its use without any a priori need to focus on a specific type of manifold creation for any combustor.

A Comparative CFD Study on Flamelet Generated Manifold and Steady Laminar Flamelet Modeling for Turbulent Flames

2013 ◽  
Author(s):  
Pravin Nakod ◽  
Rakesh Yadav ◽  
Pravin Rajeshirke ◽  
Stefano Orsino
Keyword(s):  
Laminar Flame ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Molecular Transport ◽  
Turbulent Flames ◽  
Reacting Flow ◽  
Jet Flame ◽  
Air Jet ◽  
Flamelet Generated Manifold ◽  
Laminar Flamelet

Laminar Flamelet Model (LFM) [1–2] represents the turbulent flame brush using statistical averaging of laminar flamelets whose structure is not affected by turbulence. The chemical non-equilibrium effects considered in this model are due to local turbulent straining only. In contrast, Flamelet Generated Manifold (FGM) [3] model considers that the scalar evolution, the realized trajectories on the thermo-chemical manifold in a turbulent flame is approximated by the scalar evolution similar to that in a laminar flame. This model does not involve any assumption on flame structure. Therefore, it can be successfully used to model ignition, slow chemistry and quenching effects far away from the equilibrium. In FGM, 1D premixed flamelets are solved in reaction-progress space rather than physical space. This helps better solution convergence for the flamelets over the entire mixture fraction range, especially with large kinetic mechanisms at the flammability limits [4]. In the present work, a systematic comparative study of FGM model with LFM for four different turbulent diffusion/premixed flames is presented. First flame considered in this work is methane-air flame with dilution air at the downstream. Second and third flame considered are jet flames in a coaxial flow of hot combustion products from a lean premixed flame called Cabra lifted H2 and CH4 flames [5–6] where the reacting flow associated with the central jet exhibits similar chemical kinetics, heat transfer and molecular transport as recirculation burners without the complex recirculating fluid mechanic. The fourth flame considered is Sandia flame D [7], a piloted methane-air jet flame. It is observed that the simulation results predicted by FGM model are more physical and accurate compared to LFM in all the flames presented in this work.

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 Identification of Flame Regimes in Partially Premixed Combustion from a Quasi-DNS Dataset

2020 ◽  
Author(s):  
Thorsten Zirwes ◽  
Feichi Zhang ◽  
Peter Habisreuther ◽  
Maximilian Hansinger ◽  
Henning Bockhorn ◽  
...  
Keyword(s):  
Turbulent Flame ◽  
Detailed Chemistry ◽  
Partially Premixed Combustion ◽  
Processing Step ◽  
Different Types ◽  
Partially Premixed ◽  
Definition Of ◽  
And Diffusion ◽  
Combustion Regimes ◽  
Term Analysis

Abstract Identifying combustion regimes in terms of premixed and non-premixed characteristics is an important task for understanding combustion phenomena and the structure of flames. A quasi-DNS database of the compositionally inhomogeneous partially premixed Sydney/Sandia flame in configuration FJ-5GP-Lr75-57 is used to directly compare different types of flame regime markers from literature. In the simulation of the flame, detailed chemistry and diffusion models are utilized and no turbulence and combustion models are used as the flame front and flow are fully resolved near the nozzle. This allows evaluating the regime markers as a post-processing step without modeling assumptions and directly comparing regime markers based on gradient alignment, drift term analysis and gradient free regime identification. The goal is not to find the correct regime marker, which might be impossible due to the different set of assumptions of every marker and the generally vague definition of the partially premixed regime itself, but to compare their behavior when applied to a resolved turbulent flame with partially premixed characteristics.

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.

Accuracy Verification of the Turbulent Flame LES Model by a Methane/Air Burner Flame

2015 ◽  
Author(s):  
Murase Kagenobu ◽  
Oshima Nobuyuki ◽  
Takahashi Yusuke
Keyword(s):  
Laminar Flame ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Counter Flow ◽  
Flamelet Model ◽  
Eddy Simulation ◽  
Partially Premixed Combustion ◽  
Large Eddy ◽  
Burner Flame ◽  
Les Model

This paper focuses on the numerical simulation of Sandia National Laboratories “the piloted methane/air burner flame D.” Large Eddy Simulation and 2-scalar flamelet approach are applied for the turbulent and partially premixed combustion field, which is expressed by the LES filtered equations of scalar G for tracking the flame surfaces and mixture fraction of a fuel and an oxidizer. The flamelet data consists of temperature, specific volume and laminar flame speed are calculated by the detail chemical reaction with GRI-Mech 3.0. Two kinds of flamelet data are validated; one is “equilibrium flamelet data” calculated by 0-dimensional equilibrium solution based on equilibrium model; the other is “diffusion flamelet data” calculated by 1-dimensional counter flow solution based on laminar flamelet model. Consequently, the “diffusion flamelet data” gives better result in this type of combustion field.

Investigation of Flamelet Generated Manifold Reaction Source Term Closure Models Applied to an Industrial Gas Turbine

2019 ◽  
Author(s):  
George Mallouppas ◽  
Graham Goldin ◽  
Yongzhe Zhang ◽  
Piyush Thakre ◽  
Jim Rogerson
Keyword(s):  
Gas Turbine ◽  
Source Term ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Turbulent Flame Speed ◽  
Progress Variable ◽  
Flamelet Generated Manifold ◽  
Reactor Types ◽  
Industrial Gas Turbine

Abstract Three Flamelet Generated Manifold reaction source term closure options and two different reactor types are examined with Large Eddy Simulation of an industrial gas turbine combustor operating at 3 bar. This work presents the results for the SGT-100 Dry Low Emission (DLE) gas turbine provided by Siemens Industrial Turbomachinery Ltd. The related experimental study was performed at the German Aerospace Centre, DLR, Stuttgart, Germany. The FGM model approximates the thermo-chemistry in a turbulent flame as that in a simple 0D constant pressure ignition reactors and 1D strained opposed-flow premixed reactors, parametrized by mixture fraction, progress variable, enthalpy and pressure. The first objective of this work is to compare the flame shape and position predicted by these two FGM reactor types. The Kinetic Rate (KR) model, studied in this work, uses the chemical rate from the FGM with assumed shapes, which are a Beta function for mixture fraction and delta functions for reaction progress variable and enthalpy. Another model investigated is the Turbulent Flame-Speed Closure (TFC) model with Zimont turbulent flame speed, which propagates premixed flame fronts at specified turbulent flame speeds. The Thickened Flame Model (TFM), which artificially thickens the flame to sufficiently resolve the internal flame structure on the computational grid, is also explored. Therefore, a second objective of this paper is to compare KR, TFC and TFM with the available experimental data.

scholarly journals Computational analysis on the stability and characteristics of partially premixed butane air open flames in tubular burner

2021 ◽  
pp. 320-320
Author(s):  
Zeenathul Abdul Gani ◽  
N. Muthu Saravanan
Keyword(s):  
Computational Study ◽  
Flame Temperature ◽  
Diffusion Mode ◽  
Partially Premixed Combustion ◽  
Stable Operating ◽  
Partially Premixed ◽  
Lift Off ◽  
The Stability ◽  
And Diffusion ◽  
Poor Stability

Partially premixed combustion is one of the developing areas of combustion research that has the advantages of both premixed and diffusion mode of combustion. The present work involves a computational study on the stability and characteristics of partially premixed butane-air flames. The effect of operating parameters like fuel-air ratio, primary aeration, and the presence of co-flow and co-swirl on the stability and flame characteristics has been studied. The simulation results show that the height of the flame decreases with an increase in primary aeration and also in the presence of a co-swirl stream. It has also been found that the stability of flames increases with co-swirl air but deteriorates with the presence of the co-flow air. The flame temperature increases with primary aeration and it has been observed that the peak flame temperature shifts away from the burner mouth for lower primary aeration. It has been observed that the flame stability improves with co-swirl air which is attributed to the recirculation zone created due to the swirl motion which acts as a heat source. The poor stability in the presence of co-flow air is attributed to flame stretching and aerodynamic quenching of the stretched flame lets. The lift off velocity and the stable operating range increases with equivalence ratio and also with co-swirl air.

Numerical Computation of a Turbulent Lifted Flame Using Flamelet Generated Manifold With Different Progress Variable Definitions

2015 ◽  
Author(s):  
Rakesh Yadav ◽  
Pravin Nakod
Keyword(s):  
Laminar Flame ◽  
Turbulent Flame ◽  
Molecular Transport ◽  
Scalar Dissipation ◽  
Reacting Flow ◽  
Dimensional Manifold ◽  
Progress Variable ◽  
Lifted Flame ◽  
Flamelet Generated Manifold ◽  
Laminar Flamelet

Dimension reduction is a popular and attractive approach for modeling turbulent reacting flow incorporating finite rate chemistry effects. One of the earliest and most popular approaches in this category is the Laminar Flamelet Model (LFM), which represents the turbulent flame brush using statistical averaging of laminar flamelets whose structure is not affected by turbulence. The other common reduction approach is the intrinsic low dimensional manifold (ILDM). While, the LFM has limitations in predicting the non-equilibrium effects, the ILDM model suffers in the prediction of the low temperature kinetics. A combination of the two approaches where flamelet based manifold are generated called, Flamelet Generated Manifold (FGM) model considers that the scalar evolution in a turbulent flame can be approximated by the scalar evolution similar to that in a laminar flame. This model does not involve any assumption on flame structure. Therefore, it can be successfully used to model ignition, slow chemistry and quenching effects, which are far away from equilibrium. In the FGM, the manifold can be created using different flame configurations. For premixed flames, 1D unstrained flamelets are solved in reaction-progress space. In the case of diffusion flames, a counter flow configuration is used to generate a series of steady flamelets with increasing scalar dissipation and also an unsteady laminar flamelet is generated to create the diffusion FGM manifold. In the present work, a diffusion flamelet based FGM model is compared with the FGM model using premixed unstrained flamelet configurations. The performance and predictive capabilities of the two approaches are compared for a turbulent lifted methane flame in a diluted hot co-flow environment, where the reacting flow associated with the central jet exhibits similar chemical kinetics, heat transfer and molecular transport as recirculation burners without the complex recirculating fluid structures. It is observed that though the diffusion flamelet based FGM predicts a lifted flame, but the lift off height is lower compared to the premixed configuration. A parametric study with different normalization for the progress variable is done to study its impact on the flame characteristics and the manifold created. Finally, the computations are performed for different definitions of the progress variable from previously published works. It is seen that the results are sensitive to the various progress variable definitions, particularly when the number of species are higher and involve different time scales.

scholarly journals Numerical study of turbulent normal diffusion flame CH4-air stabilized by coaxial burner

2013 ◽  
Vol 17 (4) ◽  
pp. 1207-1219 ◽  
Author(s):  
Zouhair Riahi ◽  
Ali Mergheni ◽  
Jean-Charles Sautet ◽  
Ben Nasrallah
Keyword(s):  
Equivalence Ratio ◽  
Numerical Study ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Flame Structure ◽  
Premixed Combustion ◽  
Air Jet ◽  
Fuel Jet ◽  
Jet Velocity ◽  
Lift Off

The practical combustion systems such as combustion furnaces, gas turbine, engines, etc. employ non-premixed combustion due to its better flame stability, safety, and wide operating range as compared to premixed combustion. The present numerical study characterizes the turbulent flame of methane-air in a coaxial burner in order to determine the effect of airflow on the distribution of temperature, on gas consumption and on the emission of NOx. The results in this study are obtained by simulation on FLUENT code. The results demonstrate the influence of different parameters on the flame structure, temperature distribution and gas emissions, such as turbulence, fuel jet velocity, air jet velocity, equivalence ratio and mixture fraction. The lift-off height for a fixed fuel jet velocity is observed to increase monotonically with air jet velocity. Temperature and NOx emission decrease of important values with the equivalence ratio, it is maximum about the unity.

A Comparative Computational Fluid Dynamics Study on Flamelet-Generated Manifold and Steady Laminar Flamelet Modeling for Turbulent Flames

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
Pravin Nakod ◽  
Rakesh Yadav ◽  
Pravin Rajeshirke ◽  
Stefano Orsino
Keyword(s):  
Laminar Flame ◽  
Turbulent Flame ◽  
Molecular Transport ◽  
Turbulent Flames ◽  
Jet Flames ◽  
Jet Flame ◽  
Air Jet ◽  
Flamelet Generated Manifold ◽  
Vitiated Coflow ◽  
Laminar Flamelet

The laminar flamelet model (LFM) (Peters, 1986, “Laminar Diffusion Flamelet Models in Non-Premixed Combustion,” Prog. Energy Combust. Sci., 10, pp. 319–339; Peters, “Laminar Flamelet Concepts in Turbulent Combustion,” Proc. Combust. Inst., 21, pp. 1231–1250) represents the turbulent flame brush using statistical averaging of laminar flamelets whose structure is not affected by turbulence. The chemical nonequilibrium effects considered in this model are due to local turbulent straining only. In contrast, the flamelet-generated manifold (FGM) (van Oijen and de Goey, 2000, “Modeling of Premixed Laminar Flames Using Flamelet-Generated Manifolds,” Combust. Sci. Technol., 161, pp. 113–137) model considers that the scalar evolution; the realized trajectories on the thermochemical manifold in a turbulent flame are approximated by the scalar evolution similar to that in a laminar flame. This model does not involve any assumption on flame structure. Therefore, it can be successfully used to model ignition, slow chemistry, and quenching effects far away from the equilibrium. In FGM, 1D premixed flamelets are solved in reaction-progress space rather than physical space. This helps better solution convergence for the flamelets over the entire mixture fraction range, especially with large kinetic mechanisms at the flammability limits (ANSYS FLUENT 14.5 Theory Guide Help Document, http://www.ansys.com). In the present work, a systematic comparative study of the FGM model with the LFM for four different turbulent diffusion/premixed flames is presented. The first flame considered in this work is methane-air flame with dilution air at the downstream. The second and third flames considered are jet flames in a coaxial flow of hot combustion products from a lean premixed flame called Cabra lifted H2 and CH4 flames (Cabra, et al., 2002, “Simultaneous Laser Raman-Rayleigh-LIF Measurements and Numerical Modeling Results of a Lifted Turbulent H2/N2 Jet Flame in a Vitiated Coflow,” Proc. Combust. Inst., 29(2), pp. 1881–1888; Lifted CH4/Air Jet Flame in a Vitiated Coflow, http://www.me.berkeley.edu/cal/vcb/data/VCMAData.html) where the reacting flow associated with the central jet exhibits similar chemical kinetics, heat transfer, and molecular transport as recirculation burners without the complex recirculating fluid mechanics. The fourth flame considered is a Sandia flame D (Barlow et al., 2005, “Piloted Methane/Air Jet Flames: Scalar Structure and Transport Effects,” Combust. Flame, 143, pp. 433–449), a piloted methane-air jet flame. It is observed that the simulation results predicted by the FGM model are more physical and accurate compared to the LFM in all the flames presented in this work. The autoignition-controlled flame lift-off is also captured well in the cases of lifted flames using the FGM model.

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