scholarly journals A two mixture fraction flamelet model for large eddy simulation of turbulent flames with inhomogeneous inlets

2017 ◽  
Vol 36 (2) ◽  
pp. 1767-1775 ◽  
Author(s):  
Bruce A. Perry ◽  
Michael E. Mueller ◽  
Assaad R. Masri
Keyword(s):  
Large Eddy Simulation ◽  
Mixture Fraction ◽  
Turbulent Flames ◽  
Flamelet Model ◽  
Eddy Simulation ◽  
Large Eddy

Large Eddy Simulation of the Ignition Performance in a Lean Burn Combustor

2015 ◽  
Author(s):  
Yingjie Qiao ◽  
Ronghai Mao ◽  
Yuzhen Lin
Keyword(s):  
Large Eddy Simulation ◽  
Flame Propagation ◽  
Bluff Body ◽  
Mixture Fraction ◽  
Ignition Process ◽  
Lean Burn ◽  
Flamelet Model ◽  
Flame Kernel ◽  
Eddy Simulation ◽  
Large Eddy

The ignition performance is a crucial issue for combustor design, especially when lean burn technologies are employed to reduce the NOx emission. Ignition is the initiation of a flame kernel followed by flame propagation and global establishment. The initiation of flame kernel is beyond the scope of this paper because it involves plasma formation process. The present investigation is mainly focused on flame front propagation which is modeled by solving a transport equation of reaction progress variable. Large eddy simulation (LES) with flamelet model has been employed to study the effect of various spark location under engine start condition. The numerical approach is validated by ignition experiments with turbulent bluff-body burner conducted by Ahmed and Mastorakos in Cambridge University. Mean and transient characteristics of velocity, mixture fraction and flame structures are compared with experimental data, to assess the accuracy of simulation in terms of flow structure, turbulent mixing and combustion performances. The validated LES model is then applied to study a series of physical locations of the spark plug in a single dome combustor. Successful and unsuccessful ignition sequences, time evolution of velocity and fuel/air ratio (FAR) of selected spots are recorded. Comparing the unsuccessful ignition with the successful ones, whether flame kernel enters into the CRZ and ignites the flammable mixture is a critical process which determines successful ignition. The evolution of flame kernel is correlated to flow field and fuel/air distribution to further analyze their effects on the ignition process. Since the process is highly transient, successful ignition is not only determined by parameters of spark location, but also influenced by the parameters throughout the flow path during flame propagation.

Large-Eddy Simulation of Combustion Oscillation in Premixed Combustor

1999 ◽  
Author(s):  
Tomoya Murota ◽  
Masaya Ohtsuka
Keyword(s):  
Large Eddy Simulation ◽  
Present Method ◽  
Premixed Combustion ◽  
Compressible Turbulence ◽  
Flamelet Model ◽  
Turbulent Premixed Flame ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Combustion Oscillation ◽  
Combustion Flow

To analyze combustion oscillation in the premixed combustor, a large-eddy simulation program for premixed combustion flow was developed. The subgrid scale (SGS) model of eddy viscosity type for compressible turbulence (Speziale et al., 1988) was adopted to treat the SGS fluxes. The fractal flamelet model, which utilizes the fractal properties of the turbulent premixed flame to obtain the reaction rate, was developed. Premixed combustion without oscillation was analyzed to verify the present method. The computational results showed good accordance with experimental data (Rydén et al., 1993). The combustion oscillation of an “established buzz” type in the premixed combustor (Langhorne, 1988) was also analyzed. The present method succeeded in capturing the oscillation accurately. The detailed mechanism was investigated. The appearance of the non-heat release region, which is generated because the supply of the unburnt gas into the combustion zone stagnates, and its disappearance play an important role.

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.

Validation of Species-Based Extended Coherent Flamelet Model in a Large Eddy Simulation of a Homogeneous Charge Spark Ignition Engine

2020 ◽  
Author(s):  
Y. See ◽  
M. Wang ◽  
J. Bohbot ◽  
O. Colin
Keyword(s):  
Large Eddy Simulation ◽  
Computational Cost ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Cylinder Pressure ◽  
Flamelet Model ◽  
Progress Variable ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Homogeneous Charge

Abstract The Species-Based Extended Coherent Flamelet Model (SB-ECFM) was developed and previously validated for 3D Reynolds-Averaged Navier-Stokes (RANS) modeling of a spark-ignited gasoline direct injection engine. In this work, we seek to extend the SB-ECFM model to the large eddy simulation (LES) framework and validate the model in a homogeneous charge spark-ignited engine. In the SB-ECFM, which is a recently developed improvement of the ECFM, the progress variable is defined as a function of real species instead of tracer species. This adjustment alleviates discrepancies that may arise when the numerical treatment of real species is different than that of the tracer species. Furthermore, the species-based formulation also allows for the use of second-order numeric, which can be necessary in LES cases. The transparent combustion chamber (TCC) engine is the configuration used here for validating the SB-ECFM. It has been extensively characterized with detailed experimental measurements and the data are widely available for model benchmarking. Moreover, several of the boundary conditions leading to the engine are also measured experimentally. These measurements are used in the corresponding computational setup of LES calculations with SB-ECFM. Since the engine is spark ignited, the Imposed Stretch Spark Ignition Model (ISSIM) is utilized to model this physical process. The mesh for the current study is based on a configuration that has been validated in a previous LES study of the corresponding motored setup of the TCC engine. However, this mesh was constructed without considering the additional cells needed to sufficiently resolve the flame for the fired case. Thus, it is enhanced with value-based Adaptive Mesh Refinement (AMR) on the progress variable to better capture the flame front in the fired case. As one facet of model validation, the ensemble average of the measured cylinder pressure is compared against the LES/SB-ECFM prediction. Secondly, the predicted cycle-to-cycle variation by LES is compared with the variation measured in the experimental setup. To this end, the LES computation is required to span a sufficient number of engine cycles to provide statistical convergence to evaluate the coefficient of variation (COV) in peak cylinder pressure. Due to the higher computational cost of LES, the runtime required to compute a sufficient number of engine cycles sequentially can be intractable. The concurrent perturbation method (CPM) is deployed in this study to obtain the required number of cycles in a reasonable time frame. Lastly, previous numerical and experimental analyses of the TCC engine have shown that the flow dynamics at the time of ignition is correlated with the cycle-to-cycle variability. Hence, similar analysis is performed on the current simulation results to determine if this correlation effect is well-captured by the current modeling approach.

scholarly journals Large Eddy Simulation of Autoignition in a Turbulent Hydrogen Jet Flame Using a Progress Variable Approach

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Rohit Kulkarni ◽  
Wolfgang Polifke
Keyword(s):  
Large Eddy Simulation ◽  
Mixture Fraction ◽  
Chemical Mechanism ◽  
Model Parameters ◽  
Jet Flame ◽  
Progress Variable ◽  
Eddy Simulation ◽  
Variable Approach ◽  
Tabulated Chemistry ◽  
Large Eddy

The potential of a progress variable formulation for predicting autoignition and subsequent kernel development in a nonpremixed jet flame is explored in the LES (Large Eddy Simulation) context. The chemistry is tabulated as a function of mixture fraction and a composite progress variable, which is defined as a combination of an intermediate and a product species. Transport equations are solved for mixture fraction and progress variable. The filtered mean source term for the progress variable is closed using a probability density function of presumed shape for the mixture fraction. Subgrid fluctuations of the progress variable conditioned on the mixture fraction are neglected. A diluted hydrogen jet issuing into a turbulent coflow of preheated air is chosen as a test case. The model predicts ignition lengths and subsequent kernel growth in good agreement with experiment without any adjustment of model parameters. The autoignition length predicted by the model depends noticeably on the chemical mechanism which the tabulated chemistry is based on. Compared to models using detailed chemistry, significant reduction in computational costs can be realized with the progress variable formulation.

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