Large Eddy Simulation of turbulent flames in a Trapped Vortex Combustor (TVC) – A flamelet presumed-pdf closure preserving laminar flame speed

2012 ◽  
Vol 340 (11-12) ◽  
pp. 917-932 ◽  
Author(s):  
Cindy Merlin ◽  
Pascale Domingo ◽  
Luc Vervisch
Keyword(s):  
Large Eddy Simulation ◽  
Laminar Flame ◽  
Turbulent Flames ◽  
Flame Speed ◽  
Laminar Flame Speed ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Presumed Pdf ◽  
Trapped Vortex

scholarly journals A Combustion Regime-Based Model for Large Eddy Simulation

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4934
Author(s):  
Eugenio Giacomazzi ◽  
Donato Cecere
Keyword(s):  
Large Eddy Simulation ◽  
Volume Fraction ◽  
Laminar Flame ◽  
Combustion Regime ◽  
Turbulent Flames ◽  
Scale Model ◽  
Flame Thickness ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Turbulent Premixed

The aim of this work is to propose a unified (generalized) closure of the chemical source term in the context of Large Eddy Simulation able to cover all the regimes of turbulent premixed combustion. Turbulence/combustion scale interaction is firstly analyzed: a new perspective to look at commonly accepted combustion diagrams is provided based on the evidence that actual turbulent flames can experience locally several combustion regimes although global non-dimensional numbers would locate such flames in a single specific operating point of the standard combustion diagram. The deliverable is a LES subgrid scale model for turbulent premixed flames named Localized Turbulent Scales Model (LTSM). This is founded on the estimation of the local reacting volume fraction of a computational cell that is related to the local turbulent and laminar flame speeds and to the local flame thickness.

Reactive computational fluid dynamics modelling methane–hydrogen admixtures in internal combustion engines part II: Large eddy simulation

2020 ◽  
pp. 146808742091034
Author(s):  
Jann Koch ◽  
Christian Schürch ◽  
Yuri M Wright ◽  
Konstantinos Boulouchos
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Large Eddy Simulation ◽  
Combustion Process ◽  
Flame Speed ◽  
Hydrogen Addition ◽  
Eddy Simulation ◽  
Modelling Framework ◽  
Large Eddy ◽  
Dynamics Modelling

Fuels based on admixtures of methane/natural gas and hydrogen are a promising way to reduce CO2 emissions of spark ignition engines and increase their efficiency. A lot of work was conducted experimentally, whereas only limited numerical work is available in the context of three-dimensional modelling of the full engine cycle. This work addresses this fact by proposing a reactive computational fluid dynamics modelling framework to consider the effects of hydrogen addition on the combustion process. Part I of this two-part study focuses on the modelling and crucial considerations in order to predict the mean cycle based on the G-equation combustion model using the Reynolds-averaged Navier–Stokes equations. There, the effect of increased burning speed was globally captured by increasing the flame speed coefficient A, appearing in the considered flame speed closure. The proposed simplified modelling of the early flame stage proved to be robust for the conducted hydrogen variation from 0 to 50 vol% H2 for stoichiometric and lean operation. Scope of this work, Part II, are cyclic fluctuations and the hydrogen influence thereon using large eddy simulation and the proposed modelling framework. The model is probed towards its capabilities to predict the fluctuation of the combustion process for 0 and 50 vol% H2 and correlations influencing the observed peak pressure of the individual cycle are presented. It is shown that the considered approach is capable to reproduce the cyclic fluctuations of the combustion process under the influence of hydrogen addition as well as lean operation. The importance of the early flame phase with respect to arising fluctuations is highlighted as well as the contribution of the resolved scales in terms of the flame front wrinkling.

scholarly journals Large Eddy Simulation of Premixed Combustion With a Thickened-Flame Approach

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
Ashoke De ◽  
Sumanta Acharya
Keyword(s):  
Large Eddy Simulation ◽  
Laminar Flame ◽  
Flame Structure ◽  
Reaction Rates ◽  
Premixed Combustion ◽  
Efficiency Function ◽  
Modeling Approach ◽  
Eddy Simulation ◽  
Reduced Chemistry ◽  
Large Eddy

A thickened-flame (TF) modeling approach is combined with a large eddy simulation (LES) methodology to model premixed combustion, and the accuracy of these model predictions is evaluated by comparing with the piloted premixed stoichiometric methane-air flame data of Chen et al. (1996, “The Detailed Flame Structure of Highly Stretched Turbulent Premixed Methane-Air Flames,” Combust. Flame, 107, pp. 233–244) at a Reynolds number Re=24,000. In the TF model, the flame front is artificially thickened to resolve it on the computational LES grid and the reaction rates are specified using reduced chemistry. The response of the thickened-flame to turbulence is taken care of by incorporating an efficiency function in the governing equations. The efficiency function depends on the characteristics of the local turbulence and on the characteristics of the premixed flame such as laminar flame speed and thickness. Three variants of the TF model are examined: the original thickened-flame model, the power-law flame-wrinkling model, and the dynamically modified TF model. Reasonable agreement is found when comparing predictions with the experimental data and with computations reported using a probability distribution function modeling approach. The results of the TF model are in better agreement with data when compared with the predictions of the G-equation approach.

Large Eddy Simulation of a Lean Gas Turbine Model Combustor

2009 ◽  
Author(s):  
M. Staufer ◽  
J. Janicka
Keyword(s):  
Experimental Data ◽  
Large Eddy Simulation ◽  
Flame Surface ◽  
Eddy Simulation ◽  
Partially Premixed Combustion ◽  
Large Eddy ◽  
Partially Premixed ◽  
Partially Premixed Flame ◽  
Presumed Pdf ◽  
Pdf Model

Partially premixed flames although common on many technical devices are difficult to model in numerical simulations. In this paper a Large Eddy Simulation of a lean combustor is presented. To account for mixing effects in case of partially premixed combustion, a suitable extension to the well known coherent flame model (CFM) is applied. The turbulent reaction rate of the partially premixed flame is approximated by solving an additional transport equation for the flame surface density which accounts for flame wrinkling effects as well as for the creation and destruction of flame surface due to stretch and strain effects. The variation of stoichiometry in the flame is accounted for by using a suitable presumed PDF methodology. The pdf-model represents finite rate, as well as non-equilibrium chemistry effects in the flame. The model has been validated against experimental data. The results show an overall reasonable agreement with experimental data, both in profile shapes as well as peak values.

scholarly journals Laminar flame speed of soy and canola biofuels

2012 ◽  
Vol 4 (5) ◽  
pp. 75-83 ◽  
Author(s):  
Juan-Sebastián Gómez-Meyer ◽  
Subramanyam R Gollahalli ◽  
Ramkumar N. Parthasarathy ◽  
Jabid-Eduardo Quiroga
Keyword(s):  
Flame Propagation ◽  
Equivalence Ratio ◽  
Laminar Flame ◽  
Turbulent Flames ◽  
Flame Speed ◽  
Thermochemical Property ◽  
Laminar Flame Speed ◽  
Hot Air ◽  
Maximum Value ◽  
Canola Oils

In this article, the flame speed values determined experimentally for laminar premixed flames of the vapors of two biofuels in air are presented. The laminar flame speed is a fundamental thermochemical property of fuels, and is essential for analyzing the flame propagation in practical devices, even those employing turbulent flames. The fuels obtained from transesterification of soy and canola oils are tested. Also, the diesel flames are studied to serve as a baseline for comparison. The experiments are performed with a tubular burner; pre-vaporized fuel is mixed with hot air and is ignited. The flame speed is determined at fuel-equivalence ratios of 1; 1,1 and 1,2 by recording the geometry of the flame. The experimental results show that the flame speed of biofuels is lower by about 15% than that of diesel. Also, the maximum value of flame speed is obtained at an equivalence ratio of approximately 1,1.

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