A Scale Separation Method for Pollutant Prediction in Turbulent Flames Using Transported Scalars With Flamelet Generated Manifold (FGM) Method

2018 ◽  
Author(s):  
Rakesh Yadav ◽  
Shaoping Li ◽  
Ellen Meeks
Keyword(s):  
Experimental Data ◽  
Mixture Fraction ◽  
Reaction Rates ◽  
Turbulent Flames ◽  
Separation Method ◽  
Scale Separation ◽  
Reduced Order ◽  
Progress Variable ◽  
Flamelet Generated Manifold ◽  
Key Species

In this work, a scale separation method has been proposed and implemented in the framework of Flamelet Generated Manifold (FGM) model. In this approach, first a list of slow evolving species like NO, N2O etc., are identified. Then, a separate transport equation for each of these species (called FGM scalars) is solved in addition to the mixture fraction and progress variable equations. The forward and reverse reaction rates of these slow forming species are computed in two-dimensional FGM flamelets and pre-tabulated as a function of progress variable, mixture fraction and their respective variances. At run time, the pre-tabulated probability density function (PDF) averaged production rates of these FGM scalars are used, while their tabulated reverse rates are modified with a linear scaling based on the ratio of tabulated values of the FGM scalar and the prevailing values of the FGM scalars from three dimensional CFD solution. This mechanism allows the reverse rates to provide continuous feedback and respond to the slow evolution of scalar. Other than the list of selected scalars, all other species and temperature are still computed as a function of the main progress variable and mixture fraction. Since, a small set of scalars can be used to track key species, this methodology remains computationally efficient. The current approach has been implemented into commercial CFD solver, ANSYS Fluent, and has been validated for two lab scale turbulent flames, the first one is Sandia Flame D, while the second one is a lifted turbulent methane flame in vitiated co-flow. In the current work, two additional FGM scalar transport equations are solved for CO and NO and comparisons have been made against the tabulated values as well as the experimental data. It has been seen that the scale separation methodology of these scalars leads ∼10–15% improvements in the CO mass fraction, while it reduces the peak NO formation up to 4 times leading to better agreement with experimental data compared to tabulated values. The quality of predictions from the current method is also evaluated against finite rate chemistry-based model as well as reduced order NO model. It is found that the current model has consistent results, and is an improvement over current reduced order modeling approach.

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.

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.

Development of a Multi-Phase Flamelet Generated Manifold for Spray Combustion Simulations

2020 ◽  
Author(s):  
Xu Zhang ◽  
Ran Yi ◽  
C. P. Chen
Keyword(s):  
Mixture Fraction ◽  
Diffusion Reaction ◽  
Spray Combustion ◽  
Direct Integration ◽  
Interphase Heat Transfer ◽  
Similarity Reduction ◽  
Progress Variable ◽  
Flamelet Generated Manifold ◽  
Significant Difference ◽  
Mass Fractions

Abstract In this study, a model flame of quasi-1D counterflow spray flame has been developed. The two-dimensional multiphase convection-diffusion-reaction (CDR) equations have been simplified to one dimension using similarity reduction under the Eulerian framework. This model flame is able to directly account for non-adiabatic heat loss as well as multiple combustion regimes present in realistic spray combustion processes. A spray flamelet library was generated based on the model flame. To retrieve data from the spray flamelet library, the enthalpy was used as an additional controlling variable to represent the interphase heat transfer, while the mixing and chemical reaction processes were mapped to the mixture fraction and the progress variable. The spray-flamelet/progress-variable (SFPV) approach was validated against the results from the direct integration of finite-rate chemistry as a benchmark. The SFPV approach gave a better performance in terms of temperature predictions, while the conventional gas-phase flamelet/progress-variable (FPV) approach over-predicted by nearly 20%. In terms of species mass fractions, there was no significant difference between the two, both showing good agreements with the direct integration of chemistry (DIC) model.

scholarly journals Implementation of the Semi Empirical Kinetic Soot Model Within Chemistry Tabulation Framework for Efficient Emissions Predictions in Diesel Engines

Open Physics ◽  
2019 ◽  
Vol 17 (1) ◽  
pp. 905-915
Author(s):  
Mijo Tvrdojevic ◽  
Milan Vujanovic ◽  
Peter Priesching ◽  
Ferry A. Tap ◽  
Anton Starikov ◽  
...  
Keyword(s):  
Diesel Engines ◽  
Mixture Fraction ◽  
Operating Conditions ◽  
Progress Variable ◽  
Flamelet Generated Manifold ◽  
Tabulated Chemistry ◽  
Fraction Mixture ◽  
Semi Empirical ◽  
Soot Model ◽  
Chemistry Tabulation

Abstract Soot prediction for diesel engines is a very important aspect of internal combustion engine emissions research, especially nowadays with very strict emission norms. Computational Fluid Dynamics (CFD) is often used in this research and optimisation of CFD models in terms of a trade-off between accuracy and computational efficiency is essential. This is especially true in the industrial environment where good predictivity is necessary for engine optimisation, but computational power is limited. To investigate soot emissions for Diesel engines, in this work CFD is coupled with chemistry tabulation framework and semi-empirical soot model. The Flamelet Generated Manifold (FGM) combustion model precomputes chemistry using detailed calculations of the 0D homogeneous reactor and then stores the species mass fractions in the table, based on six look-up variables: pressure, temperature, mixture fraction, mixture fraction variance, progress variable and progress variable variance. Data is then retrieved during online CFD simulation, enabling fast execution times while keeping the accuracy of the direct chemistry calculation. In this work, the theory behind the model is discussed as well as implementation in commercial CFD code. Also, soot modelling in the framework of tabulated chemistry is investigated: mathematical model and implementation of the kinetic soot model on the tabulation side is described, and 0D simulation results are used for verification. Then, the model is validated using real-life engine geometry under different operating conditions, where better agreement with experimental measurements is achieved, compared to the standard implementation of the kinetic soot model on the CFD side.

scholarly journals Simulation of CO-H2-Air Turbulent Nonpremixed Flame Using the Eddy Dissipation Concept Model with Lookup Table Approach

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Kazui Fukumoto ◽  
Yoshifumi Ogami
Keyword(s):  
Mixture Fraction ◽  
Chemical Species ◽  
Reaction Rates ◽  
Lookup Table ◽  
Direct Integration ◽  
Progress Variable ◽  
Look Up Table ◽  
Nonpremixed Flame ◽  
Combustion Simulation ◽  
The Look

We present a new combustion simulation technique based on a lookup table approach. In the proposed technique, a flow solver extracts the reaction rates from the look-up table using the mixture fraction, progress variable, and reaction time. Look-up table building and combustion simulation are carried out simultaneously. The reaction rates of the chemical species are recorded in the look-up table according to the mixture fraction, progress variable, and time scale of the reaction. Once the reaction rates are recorded, a direct integration to solve the chemical equations becomes unnecessary; thus, the time for computing the reaction rates is shortened. The proposed technique is applied to an eddy dissipation concept (EDC) model and it is validated through a simulation of a CO-H2-air nonpremixed flame. The results obtained by using the proposed technique are compared with experimental and computational data obtained by using the EDC model with direct integration. Good agreement between our method and the EDC model and the experimental data was found. Moreover, the computation time for the proposed technique is approximately 99.2% lower than that of the EDC model with direct integration.

Turbulent mean reaction rates in the limit of large activation energies

1981 ◽  
Vol 110 ◽  
pp. 411-432 ◽  
Author(s):  
N. Peters ◽  
W. Hocks ◽  
G. Mohiuddin
Keyword(s):  
Reaction Rate ◽  
Laminar Flame ◽  
Mixture Fraction ◽  
Beta Function ◽  
Reaction Rates ◽  
Activation Energies ◽  
Premixed Combustion ◽  
Flame Velocity ◽  
Progress Variable ◽  
The Mean

Closed-form expressions for the turbulent mean reaction rate and its covariance with the temperature are derived for premixed and non-premixed combustion. The limit of large activation energies is exploited for a chemical reaction rate that, by virtue of coupling functions, depends on the mixture fraction and a non-equilibrium progress variable only. The probability density function (p.d.f.) formulation with an assumed shape of the p.d.f. is used; a beta-function distribution is assumed for the progress variable. The mean reaction rate is expressed in terms of the mean and the variance of the temperature and, for non-premixed combustion, of the mixture fraction. The reaction kinetics are represented by the non-dimensional activation energy and the laminar flame velocity. For non-premixed systems the possibility of local extinction by flame stretch is considered.

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.

Performance prediction of transonic axial multistage compressor based on one-dimensional meanline method

2021 ◽  
pp. 095765092199881
Author(s):  
Yingying Zhang ◽  
Shijie Zhang
Keyword(s):  
Experimental Data ◽  
Mass Flow ◽  
Flow Separation ◽  
Performance Prediction ◽  
Factor Model ◽  
Separation Method ◽  
Prediction Program ◽  
Blockage Factor ◽  
Reliability And Robustness ◽  
Work Done

This study proposes a 1D meanline program for the modeling of modern transonic axial multistage compressors. In this method, an improved blockage factor model is proposed. Work-done factor that varies with the compressor performance conditions is added in this program, and at the same time a notional blockage factor is kept. The coefficient of deviation angle model is tuned according to experimental data. In addition, two surge methods that originated from different sources are chosen to add in and compare with the new method called mass flow separation method. The salient issues presented here deal first with the construction of the compressor program. Three well-documented National Aerodynamics and Space Administration (NASA) axial transonic compressors are calculated, and the speedlines and aerodynamic parameters are compared with the experimental data to verify the reliability and robustness of the proposed method. Results show that consistent agreement can be obtained with such a performance prediction program. It was also apparent that the two common methods of surge prediction, which rely upon either stage or overall characteristic gradients, gave less agreement than the method called mass flow separation method.

Sign in / Sign up

Export Citation Format

Share Document