DNS and LES of Turbulent Combustion

Transcription

1 Computational Fluid Dynamics In Chemical Reaction Engineering IV June 19-24, 2005 Barga, Italy DNS and LES of Turbulent Combustion Luc Vervisch INSA de Rouen, IUF, CORIA-CNRS Pascale Domingo, Julien Réveillon Sandra Payet, Cécile Péra & Raphael Hauguel 1

2 Combustion system: Turbulent flow Large Scales RANS Smaller Scales DNS LES????? -? -? -? Unsteady large scales lead to an imperfect mixing in the system. Those scales are geometry dependent and feature a long life time. Micro-mixing mechanisms bring reactants in contact within thin reaction zones. 2

3 OUTLINE DNS of turbulent combustion. Overview of turbulent combustion modeling. One example of SGS modeling in LES of premixed turbulent combustion. SGS modeling of partially premixed combustion. 3

4 Resolution needed for full simulation: Flow: Memory Speed Year Gbytes 50 Gflops Tbytes 50 Tflops Pbytes 50 Pflops 2015? J. Jiménez, Eng. Turbulence Modelling and Experiments-5, 2002 Flame (CH4/AIR) : Mizobuchi et al, Proc. Combust. Inst

5 So far, three types of full solutions (DNS): DNS of synthetic model problem (freely decaying turbulence). DNS of laboratory flame, but at much lower Re. DNS of laboratory flame. INSA Cambridge Synthetic problem Chemistry: Single-step Reduced Tabulated Detailed Sandia, Livermore Laboratory flame at lower Re JAXA Real jet-flame Transport: Fixed Lewis and Schmidt Variable Lewis & Schmidt Complex 5

6 Premixed Turbulent V-Flame RANS VIEW DNS HOT WIRE Boukhalfa & Renou, INSA de Rouen 6

7 Complex chemistry FPI-FGM: Gicquel et al Proc. Combust. Inst.Vol. 28, , Oijen et al Combust. Flame, 127(3): , OH 7

8 RANS VIEW 8

9 Overview of turbulent combustion modeling tools 9

10 Flame surface density G-Eq or c-eq Flamelet modeling CMC PDF transport 10

11 Control parameter of molecular mixing? Oxi Fuel Oxi 11

12 Conditional scalar dissipation rate Micromixing Combustion Tools Veynante & Vervisch, Prog In Energ Sci, 28: PDF 12 Surface or G-field

13 Academic combustion regimes Prémélange Diffusion Fuel + Oxidizer Φ(Ζ ο ) Products Z s Z = 0 Z = 0 Oxi Fuel Z = 1 Oxi 13

14 Premixed flame LES filtering Filtering a stoichiometric premixed Propane/Air Flame SGS fluctuation 14

15 SGS Probability Density Function in premixed flames: The thin flame front has a characteristic scale within the subgrid. The thin flame is seen at the grid scale. EFFECTS 1. Thickening by the filter of the thin flame front over the coarse LES grid. 2. Wrinkling of the flame within the subgrid that results from interaction with subgrid vortices. 15

16 Flame surface density contains information on the flame characteristic length: DNS 16

17 Filtered gradient contains two points information Laminar flame 17

18 Get the PDF from the Flame Surface Density inside the flame: 18

19 Describing SGS variance of progress variable: Energy that is not resolved by the coarse LES grid. Try to get it from resolved scales: - Scale similarity hypothesis. - Equilibrium hypothesis. Solve a balance equation to get SGS variance: - Which balance equation is the best? - Close unknown terms. 19

20 Scale similarity assumption: Filtered DNS 20

21 Equation for SGS variance: Production - Dissipation and Source Dissipation: 21

22 Equilibrium hypothesis: Depends on geometry and chemistry Filtered DNS 22

23 Chose the appropriate variable to be transported (the one that minimizes LES numerical problems ) Solve for the departure from maximum variance: Unmixedness: 0 1 S 23

24 The modeled balance equations to be solved for presuming the PDF then reads: Scalar dissipation rate Chemical source 24

25 LES CHEMICAL TABLES Averaging FGM or FPI FPI (Flame Prolongation of ILDM): Gicquel et al Proc. Combust. Inst.Vol. 28, , FGM (Flame Generated Manifod): Oijen et al Combust. Flame, 127(3): ,

26 SGE: Fully Compressible Flow. 4th ordre in space, 2nd in time. Skew symmetric like, Ducros et al, J. Comput.. Phys., 161: , Dynamic Lagrangian Modeling. Meneveau et al, JFM, , Structure Function. M. Lesieur Team. 26

27 Test premixed SGS modeling on ORACLES (Nguyen and Bruel,, AIAA ) 27

28 Time averaged streamwise velocity frozen flow mixing: 28

29 Progress variable: Time averaged streamwise velocity: 29

30 Time averaged spanwise velocity: 30

31 Time averaged spanwise velocity: 31

32 Time averaged RMS velocity: 32

33 OUTLINE DNS of turbulent combustion. Overview of turbulent combustion modeling. One example of SGS modeling for LES of premixed turbulent combustion. SGS modeling of partially premixed combustion. 33

34 Industrial combustion Nox emission control 34

35 Nonpremixed turbulent flame base: Zone 2: Diffusion properties Mixing controlled Pollution Flame length From burner Muniz & Mungal, Combust. Flame 111(1/2), 1997 Zone 1: Premixed properties Thin reaction zones Interface fresh/burnt Propagation Stabilization 35

36 Premixed/Diffusion combustion Chemistry is faster Diffusion is faster Flux in Z Diffusion flame Equilibrium Premixed Combustion Methane-air Fiorina et al. Combust. Flame, 140(3), , (2005) 36

37 Takeno s s flame index to determine combustion regime: Premixed Diffusion Fuel + Oxidizer Products Fuel Oxidizer 37

38 DNS of lifted flames: Premixed Diffusion Mixture fraction Progress variable Conditional flame index Hot air 900K St = 0.4 ξ p = n F n O Sixth order PADE, Third order time stepping, NSCBC Boundary conditions 38

39 DNS of weakly turbulent flame bases: Gaseous Spray Marley et al. FTaC 72(1), 29-47,

40 Turbulent flame base structure (gaseous case): OxidizerRich partially premixed Z s Mixing Fuel Ghosal & Vervisch, JFM, 415, (2000) 40 Li & Williams, Combust. Flame, 118(3): , (1999)

41 Amplitude of the burning rate in premixed mode: = 1 Premixed = 0 Diffusion 41

42 Fraction of premixed burning: Gaseous Spray y x Gaseous Spray 42

43 Diffusion flamelet,, but only for the diffusion-part : Gaseous Spray 43

44 Flame decomposition: Modeled decomposition: Modeled coefficients: 44

45 Modeled decomposition: Domingo et al, DNS analysis of partially premixed combustion in spray and gaseous turbulent-flame bases stabilized in hot air, Combust. Flame, 103(3): , Reveillon & Vervisch, Analysis of weakly turbulent diluted-spray flames and spray combustion regimes, JFM, 537: , Gaseous Spray 45