Alessandro Soli a Ivan Langella ab Zhi X Chen c a Loughborough University Aeronautical and Automotive Engineering b Technical University of Delft Faculty of Aerospace Engineering ID: 814712
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Slide1
The role of strain and mixture fraction variance in the prediction of local extinctions in LES of partially premixed combustion
Alessandro Solia,*, Ivan Langellaa,b, Zhi X. Chenca Loughborough University – Aeronautical and Automotive Engineering b Technical University of Delft – Faculty of Aerospace Engineeringc University of Cambridge – Department of Engineering* corresponding e-mail: a.soli@lboro.ac.uk
A. Soli, I. Langella, Z. X. Chen, UKCTRF Annual Meeting, 16th september 2020
1
Slide2Introduction | Motivation
Mechanisms behind local extinctions yet to be fully understoodNon-premixed flames: diffusion losses > local heat releasePremixed flames: flame strained by high-vorticity regionsPartially-premixed flames: less understoodSydney/Sandia jet flame with inhomogenous inlets [1,2]Local extinctions increasing as bulk velocity risesUnstrained premixed flamelets able to predict experimental data [3]Extinctions underestimated closer to blow-off [
3]Why can we predict extinctions with an unstrained flamelets formulation?
How does the mechanism change closer to blow-off?
A. Soli, I. Langella, Z. X. Chen,
UKCTRF Annual Meeting,
16th september 2020
2
1
Barlow
et al.
,
Combust. Flame 162 (10) (2015) 3516--35402 Cutcher et al., Combust. Flame 194 (2018) 439--4513 Chen et al., Combust. Flame 212 (2020) 415--432
Slide3Introduction | Test case
A. Soli, I. Langella, Z. X. Chen, UKCTRF Annual Meeting, 16th september 2020 3Sydney/Sandia jet flame with inhomogenous inlets [1,2]
Flame
[mm]
[m/s]
[m/s]
[m/s]
[%]
Lr75-80
75
80
93.8
83.4
70
Lr75-103
75
103
120.6
107.290
FlameLr75-80758093.883.470Lr75-10375103120.6107.290
: bulk flow velocity
: flame blow-off velocity
[
3
]
1
Barlow
et al.
,
Combust. Flame
162 (10) (2015) 3516--35402 Cutcher et al., Combust. Flame 194 (2018) 439--4513 Chen et al., Combust. Flame 212 (2020) 415--432
OpenFOAM12 flow-through times per flame24h on 240 ARCHER coresTotal kAUs: 3456
Slide4Turbulence and Combustion Modelling
A. Soli, I. Langella, Z. X. Chen, UKCTRF Annual Meeting, 16th september 2020 4Favre-filtered LES equations for mass, momentum and total enthalpy
, from
transport equation
Turbulence-chemistry interactions via presumed PDF (beta functions)Database of unstrained premixed flamelets (GRI 3.0)
Transport equations for combustion variables
:
premixed
non-premixed
[
3
]
3
Chen
et al.
,
Combust. Flame
212 (2020) 415--432
Slide5Turbulence and Combustion Modelling
A. Soli, I. Langella, Z. X. Chen, UKCTRF Annual Meeting, 16th september 2020 5Favre-filtered LES equations for mass, momentum and total enthalpy
, with
transport equationTurbulence-chemistry interactions via presumed PDF (beta functions)Database of unstrained premixed flamelets (GRI 3.0)
Transport equations for combustion variables
:
4
Dunstan
et al.
,
Proc. Combust. Inst.
34 (2013) 1193—1201
5
Langella
et al.
,
Combust. Theory Model.
19 (5) (2015) 628--656
6
Langella
et al., Combust. Flame 173 (2015) 161---178
[4,5,6,…]
Slide6Lagrangian tracking
A. Soli, I. Langella, Z. X. Chen, UKCTRF Annual Meeting, 16th september 2020 6Massless Lagrangian particles injected periodically from burner mouthClassified by:origin (main vs pilot)amount of fuel (reactants mixing vs co-flow mixing)mixture fraction (in vs out of flammability limits)burning status through reaction rate and threshold
[
7]
extinction threshold
7
Mitarai
et al.
,
Phys. Fluids
15 (12) (2013) 3856--3866
Slide7Results |
Lagrangian tracking | Lr75-80A. Soli, I. Langella, Z. X. Chen, UKCTRF Annual Meeting, 16th september 2020 7
injection from pilot
+
ignition
injection from main jet
+
ignition
injection from main jet
+
ignition
+
quenching67%41%7%, 1.5% stoich
.
Slide8Results | Lagrangian
tracking | Lr75-80A. Soli, I. Langella, Z. X. Chen, UKCTRF Annual Meeting, 16th september 2020 8local extinction
injection from main jet
Slide9Results | Lagrangian
tracking | Lr75-80A. Soli, I. Langella, Z. X. Chen, UKCTRF Annual Meeting, 16th september 2020 9local extinction
injection from main jet
interaction with cold reactants
high resolved strain
Slide10Results | Lagrangian
tracking | Lr75-80A. Soli, I. Langella, Z. X. Chen, UKCTRF Annual Meeting, 16th september 2020 10
t = 1.38 ms
local extinction
injection from main jet
“cold”
moderate/high SGS mixing
Slide11Results | Lagrangian
tracking | Lr75-80A. Soli, I. Langella, Z. X. Chen, UKCTRF Annual Meeting, 16th september 2020 11
t = 1.38 ms
local extinction
injection from main jet
“cold”
moderate/high SGS mixing
ms
ms
not enough time
to start burning!
Slide12Results | Eulerian analysis | Lr75-80
A. Soli, I. Langella, Z. X. Chen, UKCTRF Annual Meeting, 16th september 2020 12
t =1.72 ms
t =2.21 ms
vortex
strain
high
Slide13Results | Eulerian analysis | Lr75-80
A. Soli, I. Langella, Z. X. Chen, UKCTRF Annual Meeting, 16th september 2020 13How is this connected to the Lagrangian argument?Vortex-induced convective fluxes of and
Incoming
and outgoing
destabilizing for the flame
Indicates incoming cold reactants
Resolved strain aligns flame front to
destabilising
flux (
A
)Maximises
incoming cold reactants
Slide14Results | Lr75-103
A. Soli, I. Langella, Z. X. Chen, UKCTRF Annual Meeting, 16th september 2020 14+30% vorticity no
peak
higher SDR
Same general
behaviour
of particles
Extinction now strain controlled
No SGS mixing mechanism
Limitation of unstrained flamelets
No SGS strain
Vorticity might be over-suppressed
Slide15Summary
A. Soli, I. Langella, Z. X. Chen, UKCTRF Annual Meeting, 16th september 2020 15LES data of partially-premixed flame [3] analysed with combined Lagrangian/Eulerian approach
Combined effect of strain and SGS mixing (through
) key mechanismLinked to large eddies casting fast packets of cold reactants on flame frontLagrangian extinction of burning particles consequence – and not cause – of extinction holes
Flamelets can predict extinctions if strain is moderate and mostly at resolved level
Limitations are scope for further modelling
3
Chen
et al.
,
Combust. Flame
212 (2020) 415--432
Slide16Acknowledgements
A. Soli, I. Langella, Z. X. Chen, UKCTRF Annual Meeting, 16th september 2020 16