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Analysis of flame structure using detailed chemistry and applicability of flamelet/progress variable model in the laminar counter-flow diffusion flames of pulverized coals

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ADVANCED POWDER TECHNOLOGY 2020年第3期31卷 1302-1322页

作者： Akaotsu, Shota Matsushita, Yohsuke Aoki, Hideyuki Malalasekera, Weeratunge Tohoku Univ Grad Sch Engn Dept Chem Engn Aoba Ku 6-6-07 Aoba Sendai Miyagi 9808579 Japan Loughborough Univ Sch Mech Elect & Mfg Engn Loughborough LE11 3TU Leics England

Pulverized coal is still found in many practical devices even though it is recognized as "dirty fuel" because of its CO2 and pollutant emissions. To overcome this problem, advanced coal utilization technologies have been developed using numerical simulations. In this study, the structures of the laminar counter-flow diffusion flames of pulverized coals were investigated by performing simulations based on detailed chemistry. The high-temperature region became narrower as the coal/air ratio increased, because of the departure from the stoichiometric mixture and local quenching by the heat transfer between the gas and solid phases. Further, the applicability of the flamelet/progress-variable (FPV) model was investigated through a priori and a posteriori tests. The a priori test confirmed that the FPV model is capable of reproducing the numerical solutions obtained using the detailed chemistry, including the mass fractions of minor species. In the a posteriori test, there was a slight difference between the FPV model and detailed chemistry results due to overestimation of the progress of the chemical reactions. Given the sufficiently high accuracy of the FPV model in various numerical conditions, it can be concluded that the extended FPV model has potential for use in turbulent coal combustion simulations. (C) 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

关键词： Numerical simulation Pulverized coal combustion flamelet/progress variable model Detailed chemistry

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Representative interactive flamelet model and flamelet/progress variable model for supersonic combustion flows

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PROCEEDINGS OF THE COMBUSTION INSTITUTE 2017年第2期36卷 2937-2946页

作者： Gao, Zhenxun Jiang, Chongwen Lee, Chun-Hian Beihang Univ Sch Aeronaut Sci & Engn Natl Lab Computat Fluid Dynam Xueyuan Rd 37 Beijing 100191 Peoples R China

Two flamelet-type models are developed for supersonic combustion flows. First, the representative interactive flamelet (RIF) model is introduced to fully incorporate the local high-Mach-number effects into the flamelet library, and some algorithms specifically for supersonic flows are designed in the RIF model. Secondly, the flamelet/progress variable (FPV) model is also extended to supersonic combustion flows, based on a new compressible rescaling for the tabulated chemical source term of the progress variable. These two models, together with the steady flamelet (SF) model, are then applied in a supersonic combustion experimental case. Numerical results indicate that the RIF model induces very limited changes on the temperature and major species concentrations compared to the SF model, implying that the species concentrations in the flamelet library are not sensitive to the local high-Mach-number effects. Overall, the RIF model does not show obvious improvement on the simulation accuracy for the studied case. While for the FPV model, the obtained numerical results achieve much better agreements with the experimental data, including the temperature, major species concentrations and auto-ignition position. It is also found that the proposed compressible rescaling for the FPV model reasonably incorporates the high-Mach-number effects on the tabulated chemical source term of the progress variable and effectively improves the simulation accuracy of the FPV model for supersonic combustion flows. (C) 2016 by The Combustion Institute. Published by Elsevier Inc.

关键词： Supersonic combustion Representative interactive flamelet model flamelet/progress variable model Computational fluid dynamics

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An improved flamelet/progress variable modeling in a hydrogen-fueled scramjet

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INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 2023年第PartB期49卷 77-91页

作者： Tang, Tao Yu, Jiangfei Wang, Zhenguo Yang, Daoning Sun, Mingbo Wang, Hongbo Zhao, Guoyan Yang, Yixin Natl Univ Def Technol Coll Aerosp Sci & Engn Changsha Hunan Peoples R China Equipment Project Management Ctr Equipment Dev Dept Beijing 100089 Peoples R China

The compressible nature of the supersonic combustion flow field results in significant temperature and pressure fluctuations. In the standard flamelet/progress variable (FPV) model, not only is it difficult to specify the tabulation boundary conditions for the flamelet database, but using a single fixed flamelet database to describe the entire complex flow field will likely introduce significant errors. To account for this, an improved FPV model is proposed in this study. Dynamic adjustment of the tabulation pressure in the flamelet database is achieved by scaling the benchmark flamelet database to match the local pressure. Real-time calibration of the tabulation oxidant temperature and fuel temperature is also achieved by real-time statistics and interpolation between four flamelet databases. This allows the improved FPV model to adaptively match the target supersonic combustion flow field without the difficulty of specifying tabulation pressures and temperatures as in the standard FPV model, and it avoids the limitations imposed by the single flamelet database. An additional species transport equation is also incorporated into this model to improve species prediction. Based on the simulations of a hydrogen-fueled scramjet with low-and-high total temperature, the improved model is shown to better restore wallpressure profiles, combustion mode predictions and OH (hydroxyl radical) distributions, compared to the standard FPV model and comparable studies. This indicates that the effects of compressibility on the chemical reaction rates have been considered.(c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

关键词： Scramjet Supersonic combustion flamelet/progress variable model P pressure

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Radiative flamelet/progress variable modelling of the UMD turbulent line fires under varying oxygen concentrations

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FIRE SAFETY JOURNAL 2024年 143卷

作者： Lin, Jianhong Zhou, Hua Hawkes, Evatt R. Ma, Man-Ching Yeoh, Guan H. Univ New South Wales Sch Mech & Mfg Engn Sydney NSW 2052 Australia Tsinghua Univ Inst Aero Engine Beijing 100084 Peoples R China

Advanced combustion models for fire simulations remain challenging due to the complex interaction of turbulence, combustion and radiation. Among these models, the flamelet-based model is a promising candidate to incorporate detailed chemistry at low computational cost. To this end, flamelet large-eddy simulations (LES) are performed to investigate extinction characteristics of a turbulent line fire, which is a target case in the Measurement and Computation of Fire Phenomena (MaCFP) workshop and has been experimentally studied at the University of Maryland. Two radiative flamelet formulations are investigated: (a) the radiative laminar flamelet model (RLFM-u) and (b) the radiative flamelet/progress variable (RFPV-u) model. In the normal air case where XO2 = 21%, RLFM-u and RFPV-u perform similarly, both yield reasonable agreement with experimentally measured temperature. However, in the under-ventilated case (XO2 = 13%), RFPV-u outperforms RLFM-u as it manages to capture the local flame extinction. Two dimensionless indices are introduced to quantify the role of radiation heat loss and local strain in flame weakening. It is revealed that radiative heat loss dominates the flame weakening in the normal air case while strain-induced local extinction contributes significantly to flame weakening in under-ventilated conditions, which is only captured by RFPV-u, highlighting its advantages in predicting fires with strong extinction.

关键词： Turbulent line fires Local extinction Flame weakening flamelet/progress variable model

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Large Eddy Simulation of NO Formation in Non-Premixed Turbulent Jet Flames with flamelet/progress variable Approach

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Journal of Thermal Science 2024年第6期33卷 2399-2412页

作者： WAN Jiawei GUO Junjun WEI Zhengyun JIANG Xudong LIU Zhaohui State Key Laboratory of Coal Combustion School of Energy and Power EngineeringHuazhong University of Science and Technology(HUST)Wuhan 430074China CCRC King Abdullah University of Science and Technology(KAUST)Thuwal 23955-6900Kingdom of Saudi Arabia

To improve the NO modelling in turbulent flames,the flamelet/progress variable(FPV)model is extended by introducing NO mass fraction into the progress variable and incorporating an additional NO transport *** sets of flamelet databases are tabulated with progress variables based on major species and NO mass fraction,*** former is used for the acquisition of the main thermochemical variables,while the latter is employed for NO ***,an additional transport equation is solved to obtain the NO mass fraction,with the source term corrected using the scale similarity *** assessments are first conducted on laminar counterflow diffusion flames to identify lookup-related errors and assess the suitability of progress variable *** results show that the progress variables based on major species and NO could correctly describe the main thermochemical quantities and NO-related variables,***,the model is applied to the large eddy simulation(LES)of Sandia *** results indicate that the extended FPV model improves the NO prediction,with a mean error for NO prediction at 55%,significantly lower than those of existing FPV models(130%and 385%).The LES with the extended FPV model quantitatively captures NO suppression in the mid-range of Reynolds numbers from 22400(Flame D)to 33600(Flame E),but underestimates the NO suppression at higher Reynolds numbers from 33600 to 44800(Flame F).This underprediction is primarily attributed to the underestimation of local extinction levels in flames with high Reynolds numbers.

关键词： Sandia flames large eddy simulation flamelet/progress variable model NO emission

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LARGE EDDY SIMULATION WITH SLIDING MESH METHOD OF A SMALL-SCALE TURBOJET ENGINE 69

LARGE EDDY SIMULATION WITH SLIDING MESH METHOD OF A SMALL-SC...

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69th ASME Turbomachinery Technical Conference and Exposition (ASME Turbo Expo) (GT)

作者： Briones, Alejandro M. Rankin, Brent A. Univ Dayton Res Inst Dayton OH 45469 USA Air Force Res Lab Wright Patterson AFB OH USA

ISBN: (纸本)9780791887929

A wall-adapting local-eddy (WALE) large eddy simulation (LES) with sliding mesh method (SMM) of a small-scale turbojet engine is conducted. A multi-table compressible flamelet/progress variable (FPV) approach is used for the combustion model. The freestream pressure and temperature, fuel flow rate, and shaft angular speed are the only inputs needed for the CFD simulations. The simulations are performed at static sea level and maximum power. The simulation is initiated using a steady Reynolds-average Navier-Stokes (RANS) simulation with multiple reference frame (MRF) and FPV methods. The mass flow rate from the RANS simulation is used as an input for the transient LES/SMM/FPV turbojet simulation. The LES results are consistent with RANS simulations, cycle analyses, and experimental data in terms of total temperature and pressure at the diffuser-combustor interface, air and fuel mass flow rate, equivalence ratio, and thrust. The spatial and temporal distributions of static temperature, static pressure, and axial and azimuthal velocity at the diffuser-combustor and combustor-turbine stator interfaces are examined and discussed in detail.

关键词： full engine simulations large eddy simulations system level approach flamelet/progress variable model smallscale gas turbine engine

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Numerical Application of the flamelet model to Supersonic Turbulent Combustion

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Fluid Dynamics & Materials Processing 2022年第4期18卷 957-971页

作者： Yongkang Zheng Qinxue Jiang Hao Tian Youda Ye Jingying Wang China Aerodynamics Research and Development Center Mianyang621000China School of Energy and Power Engineering Shandong UniversityJinan250061China

In this study,the flow field structure inside a scramjet combustor is numerically simulated using the flamelet/progress variable *** injection is considered,with fuel mixing enhanced by means of a streamwise *** flow field structure and combustion characteristics are analyzed under different *** is also paid to the identification of the mechanisms that keep combustion stable and support enhanced *** overall performances of the combustion chamber are discussed.

关键词： Steady flamelet model flamelet/progress variable model supersonic combustion

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Large eddy simulation of turbulent non-premixed oxy-fuel jet flames with different Reynolds numbers

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FUEL 2024年 368卷

作者： Guo, Junjun Jiang, Xudong Im, Hong G. Liu, Zhaohui Huazhong Univ Sci & Technol Sch Energy & Power Engn State Key Lab Coal Combust Wuhan 430074 Peoples R China King Abdullah Univ Sci & Technol KAUST CCRC Thuwal 239556900 Saudi Arabia Natl Energy Res & Dev Ctr Clean & Low Carbon Coal Wuhan 430074 Peoples R China

Due to differences in the physical and chemical properties of CO2 and N2, along with a reduction in the momentum ratio between oxidant and fuel streams, the local extinction of oxy-fuel flames is significantly more pronounced compared to conventional air-fuel flames, which poses challenges in the design and operation of oxy-fuel burners. This study further validates the species-weighted flamelet/progress variable (FPV) model proposed in previous work [Jiang et al., 2023], particularly in oxy-fuel flames characterized by highly local extinction. Large eddy simulations were conducted on the Sandia oxy-fuel jet diffusion flame at various Reynolds numbers. The predictions are systematically compared with experimental data, and the influence of Reynolds number on local extinction is thoroughly analyzed. The results demonstrate that the numerical simulation effectively predicts mean temperature, species mass fractions, differential diffusion parameters (ZHC), and local extinction in oxy-fuel jet flames across a wide range of Reynolds numbers. The errors in predicted mean temperature and mass fractions exhibit a slight increase with rising Reynolds numbers, yet remain below 15 %. As the Reynolds number increases from 12,000 to 18,000, the predicted peak ZHC decreases by 30 %, and the beneficial effect of preferential diffusion of H2 weakens, while the adverse effect of CO2 on combustion becomes stronger.

关键词： Oxy-fuel combustion Large eddy simulation flamelet/progress variable model Differential diffusion

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LES of non-premixed NH3/H2/N2-air jet flames at elevated pressure with differential diffusion

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COMBUSTION AND FLAME 2024年 268卷

作者： Guo, Junjun Wang, Guoqing Tang, Hao Jiang, Xudong Abdelwahid, Suliman Hernandez-Perez, Francisco E. Guiberti, Thibault F. Roberts, William L. Magnotti, Gaetano Liu, Zhaohui Im, Hong G. King Abdullah Univ Sci & Technol KAUST CCRC Thuwal 239556900 Saudi Arabia Georgia Inst Technol Daniel Guggenheim Sch Aerosp Engn Atlanta GA 30332 USA Huazhong Univ Sci & Technol Sch Energy & Power Engn State Key Lab Coal Combust Wuhan 430074 Peoples R China

Cracking NH3 3 into a mixture of NH3/H2/N2 3 /H 2 /N 2 effectively addresses its low reactivity when used as a fuel. In this study, large eddy simulation (LES) and experiments are conducted for non-premixed NH3/H2/N2-air 3 /H 2 /N 2-air jet flames with simulated cracking ratios of 14 % and 28 % at an elevated pressure of 5 bar. Detailed experimental data on the flow field are provided for assessing turbulence models. A recently proposed species-weighted flamelet/ progress variable (SWF) model considering differential diffusion is adapted for simulating cracked NH3 3 flames. The effects of differential diffusion on scalar structures are further analyzed. The SWF model, incorporating differential diffusion, achieves good agreement with experiments in predicting velocity, mean temperature, major species mass fractions, differential diffusion parameters, and NO formation. The model also qualitatively captures variations in localized extinction along the flame height. In contrast, the unity Lewis number flamelet/ progress variable (ULF) model predicts the occurrence of localized extinction too upstream, significantly overestimating its occurrence in the near field where differential diffusion is significant. Moreover, NO formation in the cracked NH3 3 flame is well predicted by the SWF model using flamelet tables, and slightly overpredicted by the ULF model without differential diffusion.

关键词： Large eddy simulation Ammonia Hydrogen flamelet/progress variable model Differential diffusion

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Effects of infinitely fast chemistry on combustion behavior of coaxial diffusion flame predicted by large eddy simulation

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FUEL PROCESSING TECHNOLOGY 2020年第0期199卷 106226-000页

作者： Akaotsu, Shota Ozawa, Ryoma Matsushita, Yohsuke Aoki, Hideyuki Malalasekera, Weeratunge Tohoku Univ Grad Sch Engn Dept Chem Engn Aoba Ku 6-6-07 Aoba Sendai Miyagi 9808579 Japan Loughborough Univ Sch Mech Elect & Mfg Engn Loughborough LE11 3TU Leics England

Large eddy simulations (LES) based on turbulent combustion models aid the design and optimization of combustors. Of the various combustion models available, the eddy break up (EBU) model is widely used because it assumes an infinitely fast chemistry. However, omitting the actual chemical kinetics can cause unexpected behavior, and the characteristics of the combustion models need to be elucidated. Here, the effects of an infinitely fast chemistry on the combustion behavior of a coaxial diffusion flame as predicted by an LES were analyzed. Although the EBU model captured the overall behavior of the chemical species as well as the flow field, the gas temperature and mass fractions of the combustion products in the mixing region of the fuel and oxidizer streams were overestimated. In contrast, the flamelet/progress variable (FPV) model yielded results that were in better agreement with the experimental data, because while the EBU model assumes an infinitely fast chemistry, the look-up tables used in the FPV model are based on the actual chemical kinetics. As these models can be used for the CFD simulations of coal and spray combustion, the results of this study should be useful for efficiently simulating practical combustion systems.

关键词： Large eddy simulation Combustion Eddy break up model flamelet/progress variable model Flame structure

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