Transcript Slide 1
Non-premixed turbulent combustion (Flamelet Progress Variable Approach (FPVA))
Flamelet-based combustion model for compressible flows
Source term is highly non-linear The source term:
i
N j rea c
1
W i
ij K fj N k sp
1
k
'
kj
K rj N k sp
1
k
''
kj
with
K fj
A fj T
j
exp
E RT j
Transported variables
Model algorithm
All other quantities • EOS • Mixing rules NSE Turbulence Temperature • Newton iteration • Not looked up from table Combustion Tabulated chemistry • Table lookup • Pre-computed chemistry Chemistry does not account for compressibility effects and viscous heating
Flamelet models for non-premixed combustion The basic assumption is that the chemical time-scales are short enough so that reactions occur in a thin layer around stoichiometric mixture on a scale smaller than the small scales of the turbulence. Physically, the flame structure is locally one-dimensional and depends only on time and on the coordinate normal to the flame front (or on z).
This has two consequences: the structure of the reaction zone remains laminar, and diffusive transport occurs essentially in the direction normal to the surface of stoichiometric mixture. Then, the scalar transport equations can be transformed to a system where the mixture fraction is an independent coordinate. A subsequent asymptotic approximation leads to the flamelet equations.
The species mass fractions are related to the mixture fraction Z by the solution of the steady flamelet equations, parameterized by the scalar dissipation rate.
2
D
Z
x
2
Compute flamelet equations and create chemistry table from the solutions
Step 1: Step 2: Goal : Create chemistry table Inputs : batesgn.therm (thermodata) batesgn.trans (transportdata) batesgn.mech (reactions) 1) CreateBinFile batesgn.therm
batesgn.trans
thermo.bin
Introducing the assumption of a beta function sub-filter distribution of the mixture fraction leads to 2) ScanMan thermo.bin
batesgn.mech
batesgn.pre
3) FlameMaster batesgn.pre
.in (input file with start profile) Flamelet solution CreateChemTable Mum/bin/CreateChemTable Input : CreateChemTable.in
thermo.bin
Flameletlist.txt
Output : table (binary file)
Jet in crossflow for combustion 9 species 28 reactions : N2 H O2 O OH H2 H2O HO2 H2O2 Global reaction : H2 + ½ (02 + 3.76N2) fuel + air H20 + ½(3.76N2)