scholarly journals Validation of an Eulerian Stochastic Fields Solver Coupled with Reaction–Diffusion Manifolds on LES of Methane/Air Non-premixed Flames

2020 ◽  
Author(s):  
Paola Breda ◽  
Chunkan Yu ◽  
Ulrich Maas ◽  
Michael Pfitzner
Keyword(s):  
Transport Model ◽  
Reaction Diffusion ◽  
Passive Scalar ◽  
Scalar Dissipation ◽  
Combustion Model ◽  
Filtered Density Function ◽  
Detailed Chemistry ◽  
Stochastic Fields ◽  
Reduced Chemistry ◽  
Flame Behavior

AbstractThe Eulerian stochastic fields (ESF) combustion model can be used in LES in order to evaluate the filtered density function to describe the process of turbulence–chemistry interaction. The method is typically computationally expensive, especially if detailed chemistry mechanisms involving hydrocarbons are used. In this work, expensive computations are avoided by coupling the ESF solver with a reduced chemistry model. The reaction–diffusion manifold (REDIM) is chosen for this purpose, consisting of a passive scalar and a suitable reaction progress variable. The latter allows the use of a constant parametrization matrix when projecting the ESF equations onto the manifold. The piloted flames Sandia D–E were selected for validation using a 2D-REDIM. The results show that the combined solver is able to correctly capture the flame behavior in the investigated sections, although local extinction is underestimated by the ESF close to the injection plate. Hydrogen concentrations are strongly influenced by the transport model selected within the REDIM tabulation. A total solver performance increase by a factor of 81% is observed, compared to a full chemistry ESF simulation with 19 species. An accurate prediction of flame F instead required the extension of the REDIM table to a third variable, the scalar dissipation rate.

scholarly journals Implementation of the Scalar Dissipation Rate in the REDIM Concept and its Validation for the Piloted Non-Premixed Turbulent Jet Flames

2021 ◽  
Vol 23 (3) ◽  
pp. 169
Author(s):  
C. Yu ◽  
U. Maas
Keyword(s):  
Dissipation Rate ◽  
Transport Model ◽  
Turbulent Flames ◽  
Turbulent Jet ◽  
Scalar Dissipation ◽  
Scalar Dissipation Rate ◽  
Jet Flames ◽  
Reduced Chemistry ◽  
The Impact ◽  
Turbulent Jet Flames

In order to address the impact of the concentration gradients on the chemistry – turbulence interaction in turbulent flames, the REDIM reduced chemistry is constructed incorporating the scalar dissipation rate, which is a key quantity describing the turbulent mixing process. This is achieved by providing a variable gradient estimate in the REDIM evolution equation. In such case, the REDIM reduced chemistry is tabulated as a function of the reduced coordinates and the scalar dissipation rate as an additional progress variable. The constructed REDIM is based on a detailed transport model including the differential diffusion, and is validated for a piloted non-premixed turbulent jet flames (Sandia Flame D and E). The results show that the newly generated REDIM can reproduce the thermo-kinetic quantities very well, and the differential molecular diffusion effect can also be well captured.

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.

scholarly journals A three-dimensional model study of long-term mid-high latitude lower stratosphere ozone changes

2003 ◽  
Vol 3 (1) ◽  
pp. 1081-1107 ◽  
Author(s):  
M. P. Chipperfield
Keyword(s):  
High Latitude ◽  
Lower Stratosphere ◽  
Transport Model ◽  
Three Dimensional ◽  
Horizontal Resolution ◽  
Chemical Transport Model ◽  
Three Dimensional Model ◽  
Detailed Chemistry ◽  
Basic Model ◽  
Column Ozone

Abstract. We have used a 3D off-line chemical transport model (CTM) to study the causes of the observed changes in ozone in the mid-high latitude lower stratosphere from 1979–1998. The model was forced by European Centre for Medium Range Weather Forecasts (ECMWF) analyses and contains a detailed chemistry scheme. A series of model runs were performed at a horizontal resolution of 7.5°×7.5° and covered the domain from about 12 km to 30 km. The basic model performs well in reproducing the decadal evolution of the springtime depletion in the northern hemisphere (NH) and southern hemisphere (SH) high latitudes in the 1980s and early 1990s. After about 1994 the modelled interannual variability does not match the observations as well, which is probably due in part to changes in the operational ECMWF analyses – which places limits on using this dataset to diagnose dynamical trends. For mid-latitudes (35°–60°) the basic model reproduces the observed column ozone decreases from 1980 until the early 1990s. Model experiments show that the halogen trends appear to dominate this modelled decrease and of this around 30–50% is due to high-latitude processing on polar stratospheric clouds (PSCs). Dynamically induced ozone variations in the model correlate with observations over the timescale of a few years. Large discrepancies between the modelled and observed variations in the mid 1980s and mid 1990s can be largely resolved by assuming that the 11-year solar cycle (not explicitly included in the 3D model) causes a 2% (min-max) change in mid-latitude column ozone.

Budget Of The Scalar Variance Equation In A Turbulent Patch Arising From Lee Wave Breaking

2015 ◽  
Vol 10 (4) ◽  
pp. 85-94
Author(s):  
Sergey Yakovenko
Keyword(s):  
Wave Breaking ◽  
Diffusion Processes ◽  
Transport Model ◽  
Spatial Behavior ◽  
Statistical Moments ◽  
Scalar Dissipation ◽  
Algebraic Expression ◽  
Lee Wave ◽  
Scalar Variance ◽  
Variance Equation

Based on averaged data of the direct numerical simulations, statistical moments are obtained in a turbulent patch arising after lee wave overturning in a flow with stable stratification and obstacle. Temporal evolution and spatial behavior of the scalar-variance transport equation budget have been studied. A priori estimations of algebraic approximations for scalar dissipation, scalar variance and turbulent-diffusion processes in the scalar-variance equation have been carried out. Such an analysis is helpful to explore the turbulent patch in terms of statistical moments, and to verify closure hypotheses in turbulence models. In the global balance of the scalar-variance equation, the compensation of production by dissipation and advection is shown, as for the turbulent kinetic energy equation. The ratio of turbulent time scales of the scalar and velocity fields varies from 0.2 to 2.2 within the wave breaking region, and the global value of this parameter is close to unity during the quasisteady period. The algebraic expression derived from the assumption of production and dissipation balance is incorrect leading to unphysical negative values, therefore the use of the full scalarvariance equation in the turbulent transport model is justified.

COMPUTATIONAL STUDY ON COMBUSTION AND EMISSION CHARACTERISTIC OF PILOTED FLAMES BY VARYING COMPOSITION CO2 OF SIMULATED BIOGAS

2017 ◽  
Vol 79 (7-3) ◽  
Author(s):  
Khor Chin Keat ◽  
M. F. Mohd Yasin ◽  
M. A. Wahid ◽  
A. Saat ◽  
A. S. Md Yudin
Keyword(s):  
Computational Study ◽  
Flame Temperature ◽  
Dilution Effect ◽  
Co2 Concentration ◽  
Nox Emission ◽  
Combustion Model ◽  
Emission Characteristic ◽  
Measured Temperature ◽  
Flamelet Model ◽  
Detailed Chemistry

This study investigates the performance of flamelet model technique in predicting the behavior of piloted flame.A non-premixed methane flame of a piloted burner is simulated in OpenFOAM. A detailed chemistry of methane oxidation is integrated with the flamelet combustion model using probability density function (pdf) approach. The turbulence modelling adopts Reynolds Average Navier Stokes (RANS) framework with standard k-ε model. A comparison with experimental data demonstrates good agreement between the predicted and the measured temperature profiles in axial and radial directions. Recently, one of major concern with combustion system is the emission of pollution specially NOx emission. Reduction of the pollutions can be achieved by varying the composition of CO2 in biogas. In addition, the effect of the composition of biogas on NOx emission of piloted burner is still not understood. Therefore, understanding the behavior composition of CO2 in biogas is important that could affect the emission of pollution. In the present study, the use of biogas with composition of 10 to 30 percent of CO2 is simulated to study the effects of biogas composition on NOx emission. The comparison between biogas and pure methane are done based on the distribution of NOx, CO2, CH4, and temperature at different height above the burner. At varying composition of CO2 in biogas, the NOx emission for biogas with 30 percent CO2 is greatly reduced compared to that of 10 percent CO2. This is due to the reduction of the post flame temperature that is produced by the dilution effect at high CO2 concentration.  

scholarly journals A-Priori Validation of Scalar Dissipation Rate Models for Turbulent Non-Premixed Flames

2020 ◽  
Author(s):  
M. P. Sitte ◽  
C. Turquand d’Auzay ◽  
A. Giusti ◽  
E. Mastorakos ◽  
N. Chakraborty
Keyword(s):  
Dissipation Rate ◽  
A Priori ◽  
Turbulent Flames ◽  
Large Eddy Simulations ◽  
Moment Closure ◽  
Scalar Dissipation ◽  
Combustion Model ◽  
Scalar Dissipation Rate ◽  
Jet Flame ◽  
Large Eddy

Abstract The modelling of scalar dissipation rate in conditional methods for large-eddy simulations is investigated based on a priori direct numerical simulation analysis using a dataset representing an igniting non-premixed planar jet flame. The main objective is to provide a comprehensive assessment of models typically used for large-eddy simulations of non-premixed turbulent flames with the Conditional Moment Closure combustion model. The linear relaxation model gives a good estimate of the Favre-filtered scalar dissipation rate throughout the ignition with a value of the related constant close to the one deduced from theoretical arguments. Such value of the constant is one order of magnitude higher than typical values used in Reynolds-averaged approaches. The amplitude mapping closure model provides a satisfactory estimate of the conditionally filtered scalar dissipation rate even in flows characterised by shear driven turbulence and strong density variation.

Effect of Piston Crevices on 3D Simulation of a Heavy-Duty Diesel Engine Retrofitted to Natural Gas Spark Ignition

2018 ◽  
Author(s):  
Iolanda Stocchi ◽  
Jinlong Liu ◽  
Cosmin E. Dumitrescu ◽  
Michele Battistoni ◽  
Carlo Nazareno Grimaldi
Keyword(s):  
Fuel Injection ◽  
Direct Injection ◽  
Combustion Model ◽  
Heavy Duty ◽  
Ic Engine ◽  
Pressure Trace ◽  
Heavy Duty Diesel Engine ◽  
Heavy Duty Diesel ◽  
Flame Behavior ◽  
Experimental Pressure

3D CFD IC engine simulations that use a simplified combustion model based on the flamelets concept can provide acceptable results with minimum computational costs and reasonable running times. More, the simulation can neglect small combustion chamber details such as valve crevices, valve recesses and piston crevices volume. The missing volumes are usually compensated by changes in the squish volume (i.e., by increasing the clearance height of the model compared to the real engine). This paper documents some of the effects that such an approach would have on the simulated results of the combustion phenomena inside a conventional heavy-duty direct-injection CI engine, which was converted to port-fuel injection SI operation. 3D IC engine simulations with or without crevice volumes were run using the G-equation combustion model. A proper parameter choice ensured that the simulation results agreed well with the experimental pressure trace. The results show that including the crevice volume affected the mass of unburned mixture inside the squish region, which in turn influenced the flame behavior and heat release during late-combustion stages.

Large Eddy Simulation of an Enclosed Turbulent Reacting Methane Jet With the Tabulated Premixed Conditional Moment Closure Method

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Carlos Velez ◽  
Scott Martin ◽  
Aleksander Jemcov ◽  
Subith Vasu
Keyword(s):  
Turbulent Combustion ◽  
Moment Closure ◽  
Scalar Dissipation ◽  
Combustion Model ◽  
Conditional Moment ◽  
Eddy Simulation ◽  
Conditional Moment Closure ◽  
Major Species ◽  
Large Eddy ◽  
Closure Method

The tabulated premixed conditional moment closure (T-PCMC) method has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes in Reynolds-averaged Navier–Stokes (RANS) environment by Martin et al. (2013, “Modeling an Enclosed, Turbulent Reacting Methane Jet With the Premixed Conditional Moment Closure Method,” ASME Paper No. GT2013-95092). Here, the premixed conditional moment closure (PCMC) method is extended to large eddy simulation (LES). The new model is validated with the turbulent, enclosed reacting methane backward facing step data from El Banhawy et al. (1983, “Premixed, Turbulent Combustion of a Sudden-Expansion Flow,” Combust. Flame, 50, pp. 153–165). The experimental data have a rectangular test section at atmospheric pressure and temperature with an inlet velocity of 10.5 m/s and an equivalence ratio of 0.9 for two different step heights. Contours of major species, velocity, and temperature are provided. The T-PCMC model falls into the class of table lookup turbulent combustion models in which the combustion model is solved offline over a range of conditions and stored in a table that is accessed by the computational fluid dynamic (CFD) code using three controlling variables: the reaction progress variable (RPV), variance, and local scalar dissipation rate. The local scalar dissipation rate is used to account for the affects of the small-scale mixing on the reaction rates. A presumed shape beta function probability density function (PDF) is used to account for the effects of subgrid scale (SGS) turbulence on the reactions. SGS models are incorporated for the scalar dissipation and variance. The open source CFD code OpenFOAM is used with the compressible Smagorinsky LES model. Velocity, temperature, and major species are compared to the experimental data. Once validated, this low “runtime” CFD turbulent combustion model will have great utility for designing the next generation of lean premixed (LPM) gas turbine combustors.

Comparison of Combustion Models and Reaction Mechanisms for FLOX® Combustion

2009 ◽  
Author(s):  
Tobias Panne ◽  
Axel Widenhorn ◽  
Manfred Aigner
Keyword(s):  
Reaction Mechanisms ◽  
Gas Turbines ◽  
Combustion Model ◽  
Atmospheric Conditions ◽  
Flameless Combustion ◽  
High Pressure And Temperature ◽  
Detailed Chemistry ◽  
Ansys Cfx ◽  
Typical Operating Condition ◽  
Commercial Software Package

Flameless combustion is characterized by very low NOx and CO emissions. It has successfully been used in technical furnaces under atmospheric conditions for many years. For the use in modern gas turbines the combustors have to be redesigned to meet the typical operating condition, i.e. high pressure and temperature. The flameless combustion under gas turbine relevant conditions has successfully been simulated using a detailed chemistry model [1]. However computational costs and turnaround times are very high for these simulations. In this work the influence of different reduced reaction mechanisms on the heat release and on the temperature and flow field depending on the implied combustion model are investigated. As a benchmark the simulations are compared to experimental data obtained by OH* chemiluminescence and OH LIF measurements [2]. The simulations are performed on the basis of the commercial software package ANSYS CFX 11.0.

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