1 / 28

The Influence of Chemical Mechanisms on PDF Calculations of Nonpremixed Piloted Jet Flames

The Influence of Chemical Mechanisms on PDF Calculations of Nonpremixed Piloted Jet Flames. Renfeng Richard Cao and Stephen B. Pope Sibley School of the Mechanical and Aerospace Engineering Cornell University, Ithaca, NY, 14853

orrick
Download Presentation

The Influence of Chemical Mechanisms on PDF Calculations of Nonpremixed Piloted Jet Flames

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Influence of Chemical Mechanisms on PDF Calculations of Nonpremixed Piloted Jet Flames Renfeng Richard Cao and Stephen B. Pope Sibley School of the Mechanical and Aerospace Engineering Cornell University, Ithaca, NY, 14853 This work is supported by Air Force Office of Scientific Research under grant No. F-49620-00-1-0171 and the Department of Energy under Grant No. DE-FG02-90ER. Dfdfdsa

  2. Contents • Introduction • About turbulent combustion • Experimental operating conditions • Calculations on piloted jet flames • Joint PDF method • Tested mechanisms • Numerical issues • Comparison of different mechanisms • Sensitivity to reaction rates and the mixing model constant • Conclusions

  3. Why detailed chemistry calculations • Turbulent combustion is important • Research on turbulent combustion is difficult • Simplified view of chemistry has been used for many years, which often show unacceptable limitations, such as the prediction of pollutant emissions or of stability limits • With the rapid increase of computer power and the development of efficient algorithms, turbulent combustion simulations with detailed chemistry have become more and more feasible in recent years.

  4. Why piloted jet flames • Starner S.H. and R.W. Bilger, 1985 • Masri A.R., Bilger R.W. and Dibble R.W., 1988 • Masri A.R., Dibble R.W. and Barlow R.S., 1996 • Barlow, R.S., and J.H. Frank, 1998 • A.N. Karpetis and R.S. Barlow, 2002 • Creating strong turbulence-chemistry interactions in a stable flame with relatively simple fluid mechanics and turbulence structure • Demonstration of local extinction and reignition in these flames

  5. Introduction: Experimental operating conditions Dimensions: • Nozzle diameter = 7.2mm • Pilot diameter = 18.2mmMain jet: • 25% CH4 • 75% air; • Fstoic = 0.351 • Lvis ~ 67dReynolds numbers: • C-13400 • D-22400 • E-33600 • F-44800

  6. Joint PDF calculations of piloted jet flames • Previous work • Xu, Pope, 2000, ARM1 mechanism, EMST • Tang, Xu, Pope, 2000, ARM2 mechanism, EMST • Lindstedt, Louloudi, Vaos, 2000, Lindstedt mechanism, MC • The current work • Six detailed and reduced mechanisms: GRI3.0 (53 species, 325 reactions), GRI2.11, ARM2, S5G211, Skeletal, Smooke • Tested flame: Flame F (and D and E) • Autoignition • Laminar opposed-flow diffusion flame (OPPDIF)

  7. Joint PDF method • TURBULENT COMBUSTION MODEL Joint velocity-turbulent frequency-composition PDF method • Software: HYB2D Developed by Muradoglu, Caughey, Pope, Liu and Cao • MIXING MODEL EMST (Euclidean Minimum Spanning Tree) • CHEMICAL MECHANISMS GRI3.0, GRI2.11, ARM2, S5G211, skeletal, Smooke • ISAT • PARALLEL ALGORITHM Domain partitioning of particles implemented using MPI

  8. Mechanism # of species # of steps NO species References GRI 3.0 53 325 With NO GRI-Mech Web site GRI 2.11 49 277 With NO GRI-Mech Web site ARM2 19 15 With NO Sung et al., 1998 S5G211 9 5 With NO Mallampalli et al., 1996 Skeletal 16 41 Without NO James et al., 1999 Smooke 16 46 Without NO Smooke et al., 1986, Bennett Tested mechanisms

  9. Numerical Issues • Calculation domain: • Statistically steady 2D axisymmetric • Inlet profiles • Implemented using the experimental data • Numerical accuracy • Statistical identical results of parallel and serial calculations • Numerical parameters that affect the accuracy of the results

  10. Convergence with respect to the ISAT error tolerance • ISAT error tolerance is set to 2×10–5 • Less than 2% error for the test case

  11. Numerical Accuracy • Statistical identical results of parallel and serial calculations • ISAT (In Situ Adaptive Tabulation) error tolerance (2×10–5) • The number of cells in the domain ( 96 by 96 ) • The number of particles per cell (100) • The coefficients of the numerical viscosity (2=0.25 , 4=2.0 ) • The coefficients of time averaging (>2000 particle time steps with time averaging factor >600) • Generally, < 2% error for mean major species, < 5% error in the minor species • Significant statistical fluctuations can be observed in conditional rms’s downstream (which is not important for the current work).

  12. Results and discussions • Introduction • Experimental operating conditions • Calculations on piloted jet flames • Joint PDF method • Tested mechanisms • Calculation domain and boundary conditions • Numerical parameters • Results and discussion • Calculation of the velocity field and mixture fraction • Comparison of different mechanisms (1) Joint PDF calculations (2) Autoignition test (3) OPPDIF • Sensitivity to the chemical reaction rates • Sensitivity to the mixing model constant Cφ • Conclusions

  13. Velocity field Blue circles: measurements [Schneider et al.]; Red lines, PDF calculations using the GRI3.0 and the EMST mixing model with Cφ=1.5 • The calculated velocity profiles agree with the experimental data reasonably well

  14. Mixture fraction Blue circles: measurements [Barlow et al.]; Lines, PDF calculations using the GRI3.0 and the EMST mixing model Red lines: Cφ=1.5 Green lines: Cφ=2.0 • Increasing Cφ doesnot always result in decreasing of rms mixture fraction at all locations

  15. Effect of pilot temperature and comparison with previous calculations (z/D=15) z/D=15: most significant local extinction; Very sensitive to Tp PDF2DV Tp=1880K Red solid: HYB2D Tp=1880 K Blue dash: PDF2DV Tp=1880K Green dash dotted: PDF2DV Tp=1860 K Black dots: measured HYB2D Tp=1880 K PDF2DV Tp=1860 K

  16. Comparison of mechanisms with z/D=15 S5G211 Smooke: extinguished S5G211: highest conditional mean

  17. Comparison of mechanisms with autoignition and flame F (Cφ=1.5) calculations Autoignition Flame F S5G211: shortest IDT Smooke: longest IDT S5G211: highest conditional mean T Smooke: extinguished

  18. Comparison of mechanisms with autoignition and flame F (Cφ=2.0) calculations Autoignition Flame F S5G211: shortest IDT Smooke: longest IDT S5G211: highest conditional mean Smooke: lowest conditional mean

  19. OPPDIF • Yellow: Smooke • Magenta: Skeletal • Blue: GRI2.11 • Green: GRI3.0 • Maxima against strain rates Smooke: the smallest extinction strain rate Skeletal: overpredicts the CO and OH GRI3.0: has doubled level of NO than the GRI2.11

  20. YCO|ξ • Red: ARM • Blue: GRI2.11 • Green: GRI3.0 • Cyan: S5G211 • Magenta: Skeletal The skeletal overpredicts CO for ξ>0.5 at z/D=30

  21. YNO|ξ • Red: ARM • Blue: GRI2.11 • Green: GRI3.0 • Cyan: S5G211 The GRI3.0 yields higher level of the NO by a factor of two compared to the GRI2.11 and ARM2 mechanisms

  22. Sensitivity of the reaction ratesSmooke • Blue: doubled reaction rates • Red: tripled reaction rates • Get stable flame by doubled the reaction rates • 1.9 times the reaction rates still extinguished

  23. Sensitivity of the reaction ratesS5G211 • Blue: standard reaction rates • Red: tenth reaction rates • The 5-step mechanism is not a good mechanism

  24. Sensitivity to the mixing model constant Cφ C=1.2 C=1.5 z/D=15 C=2.0 C=3.0 Skeletal GRI2.11 ARM2 GRI3.0 S5G211 Smooke • More sensitive to the change when the calculations close to global extinction

  25. Maximal temperature against C at z/D=15 Measured S5G211 Skeletal GRI2.11 GRI2.11 Smooke GRI3.0 ARM2 ARM2 Smooke S5G211 GRI3.0 Measured Skeletal • Similar tendency for all mechanisms (horizontally shifted) • More sensitive to the change when the calculations close to global extinction

  26. Conclusions (1/2) • The performance of six detailed and reduced mechanisms has been investigated using the joint PDF calculations of flame F • The large number of numerically-accurate PDF calculations reported here demonstrates that this PDF/ISAT methodology can be effectively applied to turbulent flames using chemical mechanisms with of order 50 species. • For different mechanisms, longer IDTs, smaller extinction strain rate (in OPPDIF), lower conditional mean temperature (in flame F) • Sensitivities of these calculations to the reaction rates and the mixing model constant Cφ has been studied. Generally, the closer to the global extinction, the more sensitive to theses parameters.

  27. Conclusions (2/2) • The GRI and ARM mechanisms (GRI2.11, GRI3.0 and ARM2) yield comparable results in agreement with experimental data (except for NO) • As previously observed, GRI3.0 overpredicts NO by a factor of 2 • The 5-step mechanism under-predicts local extinction substantially • The Smooke mechanism has longer IDT and over-predicts local extinction • The skeletal mechanism is generally good but it over-predicts CO

  28. Thank you! Questions? Thanks and questions Thank you for your attention! Open for questions or comments

More Related