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Presented by
High Fidelity Numerical Simulationsof Turbulent Combustion
Jacqueline H. Chen (PI)Chun S. Yoo
David H. LignellCombustion Research Facility
Sandia National Laboratories, Livermore, CA
Ramanan SankaranNational Center for Computational Sciences
Oak Ridge National Laboratory
2 Chen_S3D_SC07
Direct numerical simulation (DNS) of turbulent combustion
DNS approach and role
Fully resolve all continuum scales without using sub-grid models.
Only a limited range of scales is computationally feasible.
Petascale computing = DNS with O(104) scales for cold flow.
DNS of small-scale laboratory flames. Investigate turbulence-chemistry interactions relevant in devices. Provide numerical benchmark data for predictive model validation and development.
Combustor size ~1m
Molecularreactions ~1nm
Turbulent combustion involves coupled phenomena at a wide range of scales
O(104) continuum scales
Turbulent combustionis a grand challenge
3 Chen_S3D_SC07
S3D—First principles combustion solver
Used to perform first-principles-based DNS of reacting flows
Solves compressible reacting Navier-Stokes equations
High-fidelity numerical methods
Detailed reaction kinetics andmolecular transport models
Multi-physics (sprays, radiation and soot) from SciDAC-TSTC
Ported to all major platforms
DNS provides unique fundamental insight into the chemistry-turbulence interaction
DNSPhysical models
Engineering CFD codes
(RANS, LES)
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Efficient parallel scaling
Results from weak scaling test on various Office of Science platforms
Scales to 23,000 Cray XT processors
1000
100
101 10 100 1000 10000
Number of processors
Co
st p
er g
rid
po
int
per
tim
e-st
ep (
µs)
SP3 (NERSC)
SP5 (NERSC)
Itanium(PNNL)
XT(ORNL)
Opteron(Sandia)
X1E (ORNL)
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Combustion science enabled by NCCSCO/H2 non-premixed flames (2005) 500M grid points
Flame-wall interaction (2006)
Lifted flames (2007) 1B grid points
Ethylene non-premixed flames (2007) 350M grid points
Lean premixed flames (2006)200M grid points
6 Chen_S3D_SC07
DNS of turbulent lifted H2/air jet flames in heated coflow Determine stability and
characteristics of a lifted flame
Understand flame stabilization mechanism Effect of degree of fuel-air pre-mixing Effect of turbulent flow Effect of preheating and auto-ignition
Simulation performed on Jaguar on 9000 cores and 2.5 million cpu-hrs ~1 billion grid points Detailed H2/air chemistry with
14109 DOF 9 resolved species and 21 elementary
reaction steps Jet Reynolds number = 11,000
Instantaneous volume rendering of the local mixing rate, by H. Yu and K. L. Ma of the SciDAC Institute for Ultrascale Visualization
7 Chen_S3D_SC07
Flame stabilization primarily due to autoignition
Flame stabilizes in fuel-lean mixture where the temperature is high (toward the heated air coflow) and mixing rates are low.
Hydroperoxy radical (HO2): Precursor of auto-ignition in hydrogen-air chemistry. Builds up upstream of OH and other intermediate
radicals (H and H2O2). Indicates auto-ignition should be primary
stabilization mechanism.
Instantaneous volume rendering of HO2 (ignition marker) and OH (flame marker) by H. Yu and K. L. Ma of the SciDAC Institute for Ultrascale Visualization
Temperature versus mixture fraction at various axial positions
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Stabilization depends on competition between autoignition and large-scale eddy passage
Isocontours of temperature with mixture fraction (dotted white line) and streamlines (arrowed line) averaged in time and z-direction
Correlation of stabilization point and axial velocity
and ignition
Near flame base, slightly negative or small positive axial velocity is observed (recirculation assists stabilization of flame base).
Stabilization point movement is cyclic with passage of large-eddies
9 Chen_S3D_SC07
Extinction and reignition in a nonpremixed ethylene/air turbulent jet flame Goal: study extinction reignition processes in hydrocarbon flames
Autoignition Premixed flame propagation Edge flame propagation
3D DNS of a slot jet at Re = 5120
Reduced ethylene mechanism consisting of 19 transported and 10 quasi-steady state species, with 167 reactions (Lu and Law 2007)
340 million grid points (8.16x109 DOF)
2.0 million cpu-hours; 14,112 cores on Jaguar
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Temperature history in a spanwise slice reveals extinction and reignition
Stoichiometric mixture fraction (black line)
(mm)
(m
m)
(m
m)
(mm) (mm) (mm)
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Excessive mixing quenches the flame and flame reignites by premixed flame propagation
Propagation speed of ignition front compared with laminar flame speed
Conditional mean and variance of scalar dissipation rate (mixing rate) and temperature at the flame
0.2Time (ms)
0.3 0.4 0.5 0.6 0.7
7000
T
st
(K)
st,
(1
/s)
st
T
6000
5000
4000
3000
2000
0
1000
0 0.1 0.2 0.3 0.4 0.5 0.6Time (ms)
800
1200
1600
2000
2400
SD*SL
Me
an
YC
O2 s
urf
ac
e S
pe
ed
(c
m/s
)
300
200
100
0
-200
-100
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Contacts
Jacqueline H. ChenPrincipal InvestigatorCombustion Research FacilitySandia National LaboratoriesLivermore, CA [email protected]
Ramanan SankaranScientific Computing liaisonNational Center for Computational SciencesOak Ridge National [email protected]
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