A New Assumed PDF Turbulent Combustion Model for Multi-Step Chemistry

2005 ◽  
Author(s):  
Baifang Zuo ◽  
David L. Black ◽  
Clifford E. Smith
Keyword(s):  
Monte Carlo ◽  
Turbulent Combustion ◽  
Diffusion Flames ◽  
Mixture Fraction ◽  
Premixed Flames ◽  
Flame Stabilization ◽  
Combustion Model ◽  
Main Stream ◽  
Wide Range ◽  
Partially Premixed

The effect of turbulence on chemical reactions is known to be important in many gas turbine combustor applications. There are only a few established models that can capture turbulence-combustion interaction in CFD codes, and all of these models are either very expensive (e.g. Monte Carlo PDF model) or limited in what types of flames can be analyzed (e.g. laminar flamelet). Assumed PDF models have been a popular choice because they are inexpensive and can handle all flame types (e.g. diffusion, premixed and partially premixed). However, assumed PDF models are typically restricted to single, one-step global mechanisms; or are a function of species and quickly become computationally expensive. CFD Research Corporation has recently developed and validated a new assumed PDF turbulence chemistry interaction model for multi-step chemistry. The model adopts an assumed, two-variable joint-PDF to model a wide-range of turbulent reacting flows. The two variables defining the PDF are the mixture fraction and reaction progress, representing species diffusion and flame propagation. A significant advantage of this new approach is its wide range of applicability for premixed, diffusion, and partially premixed flames. Allowing more detailed chemistry for species and combustion predictions enables complex chemical reaction processes including pollutant formation, flame ignition, and flame quenching to be studied. The model is also computationally efficient, with only a minor increase in computational expense with either species or number of global reaction steps. The newly developed model was first validated using a diffusion flame from a piloted burner developed at the University of Sydney. Three different methane bulk jet velocities were used to investigate the model’s behavior on turbulent diffusion flames. Simulation data were compared with the experimental measurements and the simulation results performed by Pope (Masri and Pope, 1990) using a velocity-composition joint PDF transport equation solved by the Monte Carlo method. To validate the model on premixed flames, the data of Moreau et al. (Moreau et al., 1974, 1976, 1977) were used. Data were collected on a mixing layer stabilized burner, where the main flow into the combustor was a premixed mixture of methane and air. Parallel to the main stream, a pilot stream of hot combustion products at 2000 K was injected for flame stabilization. The results demonstrate the wide applicability of the new model for practical, turbulent combustion applications.

scholarly journals Study of the Wall Thermal Condition Effect in a Lean-Premixed Downscaled Can Combustor Using Large-Eddy Simulation

2016 ◽  
Author(s):  
D. Mira ◽  
M. Vázquez ◽  
G. Houzeaux ◽  
S. Gövert ◽  
J. W. B. Kok ◽  
...  
Keyword(s):  
Turbulent Combustion ◽  
Mixture Fraction ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Laminar Flames ◽  
Combustion Model ◽  
Test Case ◽  
Eddy Simulation ◽  
Condition Effect ◽  
Large Eddy

The primary purpose of this study is to evaluate the ability of LES, with a turbulent combustion model based on steady flamelets, to predict the flame stabilization mechanisms in an industrial can combustor at full load conditions. The test case corresponds to the downscaled Siemens can combustor tested in the high pressure rig at the DLR. The effects of the wall temperature on the prediction capabilities of the codes is investigated by imposing several heat transfer conditions at the pilot and chamber walls. The codes used for this work are Alya and OpenFOAM, which are well established CFD codes in the fluid mechanics community. Prior to the simulation, results for 1-D laminar flames at the operating conditions of the combustor are compared with the detailed solutions. Subsequently, results from both codes at the mid-plane are compared against the experimental data available. Acceptable results are obtained for the axial velocity, while discrepancies are more evident for the mixture fraction and the temperature, particularly with Alya. However, both codes showed that the heat losses influence the size and length of the pilot and main flame.

Modeling of Turbulent Combustion Process and Lean Blow Out Using Combined Approach

2008 ◽  
Author(s):  
Yu. G. Kutsenko ◽  
S. F. Onegin ◽  
L. Y. Gomzikov
Keyword(s):  
Combustion Chamber ◽  
Bluff Body ◽  
Diffusion Flames ◽  
Premixed Flames ◽  
Combustion Process ◽  
Flame Stabilization ◽  
Combustion Model ◽  
Main Zone ◽  
Lean Premixed ◽  
No Emissions

Most of the modern combustor’s designs use staged concepts for reducing thermal NO emissions. Usually, a combustion process takes place inside the main zone, which uses very lean premixed fuel/air mixtures. A diffusion pilot zone supports combustion process inside a lean main zone. Thermal NO formation process takes place predominantly inside hot diffusion flame. So, operation modes of pilot and main zones must be arranged to provide low NO emissions of pilot zone and maintain flame stability inside the main zone simultaneously. In this paper a concept of new turbulent model combustion model is presented. This model allows to model diffusion and premixed flames and takes into account various physical processes, which lead to flame destabilization. The model uses an equation for reaction progress variable. In the frameworks of considered approach this equation has three source terms. These terms are responsible for different conditions of combustion process: diffusion flames, premixed flames and distributed reaction zones. A proposed model was widely validated for different types of combustion chambers such as: 1) Bluff-body flameholder (lean premixed combustion: modeling of lean blow out); 2) Conventional diffusion regime of combustion chamber of gas turbine engine (modeling of flame stabilization and NO emissions); 3) Combined combustion regime of combustion chamber: burning process is inside pilot diffusion and main premixed zones (NO emissions and lean blow out limits for several operational modes). These tests had shown a good agreement of experimentally obtained data with results of simulations.

Modeling of Turbulent Combustion Process and Lean Blowout of Diffusion and Premixed Flames Using a Combined Approach

2009 ◽  
Author(s):  
Yu. G. Kutsenko ◽  
A. A. Inozemtsev ◽  
L. Y. Gomzikov
Keyword(s):  
Diffusion Flame ◽  
Turbulent Combustion ◽  
Diffusion Flames ◽  
Premixed Flames ◽  
Combustion Process ◽  
Combustion Model ◽  
Main Zone ◽  
Lean Blowout ◽  
No Formation ◽  
No Emissions

Most of the modern combustor’s designs use staged concepts for reducing thermal NO emissions. Usually, a combustion process takes place inside the main zone, which uses very lean premixed fuel/air mixtures. A diffusion pilot zone supports combustion process inside a lean main zone. Thermal NO formation process takes place predominantly inside hot diffusion flame. So, operation modes of pilot and main zones must be arranged to provide low NO emissions of pilot zone and maintain flame stability inside the main zone simultaneously. In this paper, a new turbulent combustion model is presented. This model allows to model diffusion and premixed flames and takes into account various physical processes, which lead to flame destabilization. The model uses an equation for reaction progress variable. Within the considered approach this equation has two source terms. These terms are responsible for different conditions of combustion process: diffusion flames and premixed flames, and distributed reacting zones. This paper studies the problem, concerning modeling of lean blowout process of diffusion flame front. To test the proposed combustion model we have simulated lean blowout process inside combustion zone of a gas turbine combustor. Good predictions of lean blowout limits were obtained.

Comparison of Temperature Fields and Emissions Predictions Using Both an FGM Combustion Model, With Detailed Chemistry, and a Simple Eddy Dissipation Combustion Model With Simple Global Chemistry

2017 ◽  
Author(s):  
Pierre Q. Gauthier
Keyword(s):  
Mixture Fraction ◽  
Temperature Fields ◽  
Combustion Model ◽  
Detailed Chemistry ◽  
Combustion Modeling ◽  
Flamelet Generated Manifold ◽  
Wide Range ◽  
Turbulence Effects ◽  
Air Chemistry ◽  
Dissipation Model

The detailed modeling of the turbulence-chemistry interactions occurring in industrial flames has always been the leading challenge in combustion Computational Fluid Dynamics (CFD). The wide range of flame types found in Industrial Gas Turbine Combustion systems has exacerbated these difficulties greatly, since the combustion modeling approach must be able to predict the flames behavior from regions of fast chemistry, where turbulence has no significant impact on the reactions, to regions where turbulence effects play a significant role within the flame. One of these combustion models, that is being used more and more in industry today, is the Flamelet Generated Manifold (FGM) model, in which the flame properties are parametrized and tabulated based on mixture fraction and flame progress variables. This paper compares the results obtained using an FGM model, with a GRI-3.0 methane-air chemistry mechanism, against the more traditional Industrial work-horse, Finite-Rate Eddy Dissipation Model (FREDM), with a global 2-step Westbrook and Dryer methane-air mechanism. Both models were used to predict the temperature distributions, as well as emissions (NOx and CO) for a conventional, non-premixed, Industrial RB211 combustion system. The object of this work is to: (i) identify any significant differences in the predictive capabilities of each model and (ii) discuss the strengths and weakness of both approaches.

Numerical Analysis of Equivalence Ratio Fluctuations in a Partially Premixed Gas Turbine Combustor Using Large Eddy Simulations

2018 ◽  
Vol 141 (4) ◽  
Author(s):  
Ping Wang ◽  
Qian Yu ◽  
Prashant Shrotriya ◽  
Mingmin Chen
Keyword(s):  
Reaction Mechanism ◽  
Equivalence Ratio ◽  
Flame Temperature ◽  
Premixed Flames ◽  
Large Eddy Simulations ◽  
Combustion Model ◽  
Inlet Channel ◽  
Large Eddy ◽  
Partially Premixed Flames ◽  
Partially Premixed

In the present work, the fluctuations of equivalence ratio in the PRECCINSTA combustor are investigated via large eddy simulations (LES). Four isothermal flow cases with different combinations of global equivalence ratios (0.7 or 0.83) and grids (1.2 or 1.8 million cells) are simulated to study the mixing process of air with methane, which is injected into the inlet channel through small holes. It is shown that the fluctuations of equivalence ratio are very large, and their ranges are [0.4, 1.3] and [0.3, 1.2] for cases 0.83 and 0.7, respectively. For simulating turbulent partially premixed flames in this burner with the well-known dynamically thickened flame (DTF) combustion model, a suitable multistep reaction mechanism should be chosen aforehand. To do that, laminar premixed flames of 15 different equivalence ratios are calculated using three different methane/air reaction mechanisms: 2S_CH4_BFER, 2sCM2 reduced mechanisms and GRI-Mech 3.0 detailed reaction mechanism. The variations of flame temperature, flame speed and thickness of the laminar flames with the equivalence ratios are compared in detail. It is demonstrated that the applicative equivalence ratio range for the 2S_CH4_BFER mechanism is [0.5, 1.3], which is larger than that of the 2sCM2 mechanism [0.5, 1.2]. Therefore, it is recommended to use the 2S_CH4_BFER scheme to simulate the partially premixed flames in the PRECCINSTA combustion chamber.

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

scholarly journals Turbulent Combustion Modelling and Experiments: Recent Trends and Developments

2019 ◽  
Vol 103 (4) ◽  
pp. 847-869 ◽  
Author(s):  
A. Giusti ◽  
E. Mastorakos
Keyword(s):  
Turbulent Combustion ◽  
Mixture Fraction ◽  
Moment Closure ◽  
Combustion Model ◽  
Complex Geometries ◽  
Conditional Moment ◽  
Practical Applications ◽  
Spray Flames ◽  
Reaction Zones ◽  
Soot Emissions

AbstractThe development of better laser-based experimental methods and the fast rise in computer power has created an unprecedented shift in turbulent combustion research. The range of species and quantities measured and the advent of kHz-level planar diagnostics are now providing great insights in important phenomena and applications such as local and global extinction, pollutants, and spray combustion that were hitherto unavailable. In simulations, the shift to LES allows better representation of the turbulent flow in complex geometries, but despite the fact that the grid size is smaller than in RANS, the push towards realistic conditions and the need to include more detailed chemistry that includes very fast species and thin reaction zones emphasize the necessity of a sub-grid turbulent combustion model. The paper discusses examples from current research with experiments and modelling that focus on flame transients (self-excited oscillations, local extinction), sprays, soot emissions, and on practical applications. These demonstrate how current models are being validated by experimental data and the concerted efforts the community is taking to promote the modelling tools to industry. In addition, the various coordinated International Workshops on non-premixed, premixed, and spray flames, and on soot are discussed and some of their target flames are explored. These comprise flames that are relatively simple to describe from a fluid mechanics perspective but contain difficult-to-model combustion problems such as extinction, pollutants and multi-mode reaction zones. Recently, swirl spray flames, which are more representative of industrial devices, have been added to the target flames. Typically, good agreement is found with LES and some combustion models such as the progress variable - mixture fraction flamelet model, the Conditional Moment Closure, and the Transported PDF method, but predicting soot emissions and the condition of complete extinction in complex geometries is still elusive.

Numerical Investigations of NOx Emissions of a Partially Premixed Burner for Natural Gas Operations in Industrial Gas Turbine

2014 ◽  
Author(s):  
Alessandro Innocenti ◽  
Antonio Andreini ◽  
Andrea Giusti ◽  
Bruno Facchini ◽  
Matteo Cerutti ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Turbulent Combustion ◽  
Fuel Injection ◽  
Formation Rate ◽  
Operating Conditions ◽  
Combustion Model ◽  
Nox Emissions ◽  
Air Concentration ◽  
Partially Premixed ◽  
Industrial Gas Turbine

In the present paper a numerical analysis of a low NOx partially premixed burner for industrial gas turbine applications is presented. The first part of the work is focused on the study of the premixing process inside the burner. Standard RANS CFD approach was used: k–ε turbulence model was modified and calibrated in order to find a configuration able to fit available experimental profiles of fuel/air concentration at the exit of the burner. The resulting profiles at different test points have been used to perform reactive simulations of an experimental test rig, where exhaust NOx emissions were measured. An assessment of the turbulent combustion model was carried out with a critical investigation of the expected turbulent combustion regimes in the system and taking into account the partially premixed nature of the flame due to the presence of diffusion type pilot flames. A reliable numerical setup was discovered by comparing predicted and measured NOx emissions at different operating conditions and at different split ratio between main and pilot fuel. In the investigated range, the influence of the premixer in the NOx formation rate was found to be marginal if compared with the pilot flame one. The calibrated numerical setup was then employed to explore possible modifications to fuel injection criteria and fuel split, with the aim of minimizing exhaust NOx emissions. This preliminary numerical screening of alternative fuel injection strategies allowed to define a set of advanced configurations to be investigated in future experimental tests.

Design Improvement Survey for NOx Emissions Reduction of a Heavy-Duty Gas Turbine Partially Premixed Fuel Nozzle Operating With Natural Gas: Numerical Assessment

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Alessandro Innocenti ◽  
Antonio Andreini ◽  
Bruno Facchini ◽  
Matteo Cerutti ◽  
Gianni Ceccherini ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Turbulent Combustion ◽  
Operating Conditions ◽  
Combustion Model ◽  
Formation Mechanisms ◽  
Heavy Duty ◽  
Flamelet Generated Manifold ◽  
Fuel Nozzle ◽  
Partially Premixed ◽  
Heavy Duty Gas Turbine

A numerical investigation of a low NOx partially premixed fuel nozzle for heavy-duty gas turbine applications is presented in this paper. Availability of results from a recent test campaign on the same fuel nozzle architecture allowed the exhaustive comparison study presented in this work. At first, an assessment of the turbulent combustion model was carried out, with a critical investigation of the expected turbulent combustion regimes in the system and taking into account the partially premixed nature of the flame due to the presence of diffusion type pilot flames. In particular, the fluent partially premixed combustion model and a flamelet approach are used to simulate the flame. The laminar flamelet database is generated using the flamelet generated manifold (FGM) chemistry reduction technique. Species and temperature are parameterized by mixture fraction and progress variable. Comparisons with calculations with partially premixed model and the steady diffusion flamelet (SDF) database are made for the baseline configuration in order to discuss possible gains associated with the introduced dimension in the FGM database (reaction progress), which makes it possible to account for nonequilibrium effects. Numerical characterization of the baseline nozzle has been carried out in terms of NOx. Computed values for both the baseline and some alternative premixer designs have been then compared with experimental measurements on the reactive test rig at different operating conditions and different split ratios between main and pilot fuel. Numerical results allowed pointing out the fundamental NOx formation processes, both in terms of spatial distribution within the flame and in terms of different formation mechanisms. The obtained knowledge would allow further improvement of fuel nozzle design.

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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