Investigation of lengthscales, scalar dissipation, and flame orientation in a piloted diffusion flame by LES

Abstract This work investigates the structure of a diffusion flame in terms of lengthscales, scalar dissipation, and flame orientation by using large eddy simulation. This has been performed for a turbulent, non-premixed, piloted methane/air jet flame (Flame D) at a Reynolds-number of 22,400. A steady flamelet model, which was represented by artificial neural networks, yields species mass fractions, density, and viscosity as a function of the mixture fraction. This will be shown to suffice to simulate such flames. To allow to examine scalar dissipation, a grid of 1.97 × 10 6 nodes was applied that resolves more than 75% of the turbulent kinetic energy. The accuracy of the results is assessed by varying the grid-resolution and by comparison to experimental data by Barlow, Frank, Karpetis, Schneider (Sandia, Darmstadt), and others. The numerical procedure solves the filtered, incompressible transport equations for mass, momentum, and mixture fraction. For subgrid closure, an eddy viscosity/diffusivity approach is applied, relying on the dynamic Germano model. Artificial turbulent inflow velocities were generated to feature proper one- and two-point statistics. The results obtained for both the one- and two-point statistics were found in good agreement to the experimental data. The PDF of the flame orientation shows the tilting of the flame fronts towards the centerline. Finally, the steady flamelet approach was found to be sufficient for this type of flame unless slowly reacting species are of interest.

[1]  F. Williams,et al.  Turbulent Reacting Flows , 1981 .

[2]  Johannes Janicka,et al.  Prediction of finite chemistry effects using large eddy simulation , 2002 .

[3]  N. Peters,et al.  Unsteady flamelet modeling of turbulent hydrogen-air diffusion flames , 1998 .

[4]  H. Pitsch,et al.  Large-eddy simulation of a turbulent piloted methane/air diffusion flame (Sandia flame D) , 2000 .

[5]  Sharath S. Girimaji,et al.  ANALYSIS AND MODELING OF SUBGRID SCALAR MIXING USING NUMERICAL DATA , 1995 .

[6]  Heinz Pitsch,et al.  IMPROVED POLLUTANT PREDICTIONS IN LARGE-EDDY SIMULATIONS OF TURBULENT NON-PREMIXED COMBUSTION BY CONSIDERING SCALAR DISSIPATION RATE FLUCTUATIONS , 2002 .

[7]  R. Barlow,et al.  The structure of turbulent nonpremixed flames revealed by Raman-Rayleigh-LIF measurements , 1996 .

[8]  R. Bilger,et al.  Conditional moment closure (CMC) predictions of a turbulent methane-air jet flame , 2001 .

[9]  Elaine S. Oran,et al.  Numerical Simulation of Reactive Flow , 1987 .

[10]  Robert S. Barlow,et al.  Measurements of scalar dissipation in a turbulent piloted methane/air jet flame , 2002 .

[11]  H. Mongia,et al.  Large-Eddy Simulation of a Gas Turbine Combustor Flow , 1999 .

[12]  N. Peters.  Laminar flamelet concepts in turbulent combustion , 1988 .

[13]  Robert J. Kee,et al.  On reduced mechanisms for methaneair combustion in nonpremixed flames , 1990 .

[14]  Heinz Pitsch,et al.  Scalar mixing and dissipation rate in large-eddy simulations of non-premixed turbulent combustion , 2000 .

[15]  R. Barlow,et al.  Effects of turbulence on species mass fractions in methane/air jet flames , 1998 .

[16]  Stephen B. Pope,et al.  PDF calculations of turbulent nonpremixed flames with local extinction , 2000 .

[17]  D. B. Spalding,et al.  Turbulent shear flows , 1980 .

[18]  Denis Veynante,et al.  LES of Chemical and Acoustic Forcing of a Premixed Dump Combustor , 2000 .

[19]  Norbert Peters,et al.  Scalar dissipation rates in turbulent jets and jet diffusion flames , 1989 .

[20]  Johannes Janicka,et al.  Efficient Generation of Initial- and Inflow-Conditions for Transient Turbulent Flows in Arbitrary Geometries , 2005 .

[21]  J. Janicka,et al.  Flow field measurements of stable and locally extinguishing hydrocarbon-fuelled jet flames , 2003 .

[22]  A. Sadiki,et al.  A digital filter based generation of inflow data for spatially developing direct numerical or large eddy simulations , 2003 .

[23]  C. Pierce,et al.  Progress-variable approach for large-eddy simulation of turbulent combustion , 2001 .

[24]  P. Moin,et al.  A dynamic subgrid‐scale eddy viscosity model , 1990 .

[25]  W. K. Bushe,et al.  Large eddy simulation of a turbulent reacting jet with conditional source-term estimation , 2001 .