Turbulent mixing and autoignition of $H2$-rich fuels at relevant reheat combustor operating conditions are investigated in the present numerical study. The flow configuration under consideration is a fuel jet perpendicularly injected into a crossflow of hot flue gas ($T>1000K,p=15$ bar). Based on the results of the experimental study for the same flow configuration and operating conditions, two different fuel blends are chosen for the numerical simulations. The first fuel blend is a $H2$/natural gas/$N2$ mixture at which no autoignition events were observed in the experiments. The second fuel blend is a $H2$/$N2$ mixture at which autoignition in the mixing section occurred. First, the non-reacting flow simulations are performed for the $H2$/natural gas/$N2$ mixture in order to compare the accuracy of different turbulence modeling methods. Here, the steady-state Reynolds-averaged Navier- Stokes (RANS) as well as the unsteady scale-adaptive simulation (SAS) turbulence modeling methods are applied. The velocity fields obtained in both simulations are directly validated against experimental data. The SAS method shows better agreement with the experimental results. In the second part of the present work, the autoignition of the $H2$/$N2$ mixture is numerically studied using the 9-species 21-steps reaction mechanism of O’Conaire et al. (Int. J. Chem. Kinet., 36(11), 2004). As in the reference experiments, autoignition can be observed in the simulations. Influences of the turbulence modeling as well as of the hot flue gas temperature are investigated. The onset and the propagation of the ignition kernels are studied based on the SAS modeling results. The obtained numerical results are discussed and compared with data from experimental autoignition studies.

## References

1.
Lieuwen
,
T.
,
McDonnel
,
V.
,
Petersen
,
E.
, and
Santavicca
,
D.
, 2008, “
Fuel Flexibility Influences on Premixed Combustor Blowout, Flashback, Autoignition and Stability
,”
J. Eng. Gas Turbines Power
,
130
, pp.
1
10
.
2.
Joos
,
F.
,
Brunner
,
P.
,
Schulte-Werning
,
B.
,
Syed
,
K.
, and
Eroglu
,
A.
, 1996, “
Development of the Sequential Combustion System for the ABB GT24/GT26 Gas Turbine Family
,” ASME Paper No. 1996–GT-315.
3.
Güthe
,
F.
,
Hellat
,
J.
, and
Flohr
,
P.
, 2009, “
The Reheat Concept: The Proven Pathway to Ultralow Emissions and High Efficiency and Flexibility
,”
J. Eng. Gas Turbines Power
,
131
(
2
), p.
021503
.
4.
Fleck
,
J. M.
,
Griebel
,
P.
,
Steinberg
,
A. M.
,
Stöhr
,
M.
, and
Aigner
,
M.
, 2010, “
Experimental Investigation of a Generic, Fuel Flexible Reheat Combustor of a Gas Turbine Relevant Operating Conditions
,” ASME Paper No. GT2010-22722.
5.
Fleck
,
J.
,
Griebel
,
P.
,
Steinberg
,
A. M.
,
Stöhr
,
M.
,
Aigner
,
M.
, and
Ciani
,
A.
, 2011, “
Autoignition Limits of Hydrogen at Relevant Reheat Combustor Operating Conditions
,” ASME Paper No. GT2011–46195.
6.
Egorov
,
Y.
, and
Menter
,
F.
, 2008, “
Development and Application of SST-SAS Turbulence Model in the DESIDER Project
,”
,
S.-H.
Peng
and
W.
Haase
, eds.,
Springer-Verlag
,
Berlin
, pp.
261
270
.
7.
Menter
,
F. R.
, 2009, “
Review of the Shear-Stress Transport Turbulence Model Experience from an Industrial Perspective
,”
Int. J. Comput. Fluid Dyn.
,
23
(
4
), pp.
305
316
.
8.
Esch
,
T.
, and
Menter
,
F. R.
, 2003, “
Heat Transfer Prediction based on Two-Equation Turbulence Models with Advanced Wall Treatment
,”
Turbulence, Heat and Mass Transfer
, Vol.
4
,
K.
Hanjalic
,
Y.
Nagano
, and
M.
Tummers
, eds.,
Begell House Inc.
,
Redding, CT
.
9.
Menter
,
F. R.
, and
Egorov
,
Y.
, 2005, “
A Scale-Adaptive Simulation Model using Two-Equation Models
,” AIAA Paper No. 2005-1095.
10.
Ivanova
,
E.
,
Noll
,
B.
,
Di Domenico
,
M.
, and
Aigner
,
M.
, 2009, “
Unsteady Simulations of Flow Field and Scalar Mixing in Transverse Jets
,” ASME Paper No. GT2009-59147.
11.
Ivanova
,
E.
,
Noll
,
B.
, and
Aigner
,
M.
, 2010, “
Computational Modelling of Turbulent Mixing of a Transverse Jet
,” ASME Paper No. GT2010-22764.
12.
Di Domenico
,
M.
,
Kutne
,
P.
,
Naumann
,
C.
,
Herzler
,
J.
,
,
R.
,
Stoehr
,
M.
,
Noll
,
B.
, and
Aigner
,
M.
, 2009, “
Numerical and Experimental Investigation of a Semi-Technical Scale Burner Employing Model Syntetic Fuels
,” ASME Paper No. GT2009-59308.
13.
O’Conaire
,
M.
,
Curran
,
H.
,
Simmie
,
J.
,
Pitz
,
R.
, and
Westbrook
,
C.
, 2004, “
A Comprehensive Modeling Study of Hydrogen Oxidation
,”
Int. J. Chem. Kinet.
,
36
(
11
), pp.
602
622
.
14.
Patankar
,
S. V.
, 1980,
Numerical Heat Transfer and Fluid Flow (Hemisphere Series on Computational Methods in Mechanics and Thermal Science)
,
Hemisphere Publishing Corporation
,
Bristol, PA
.
15.
Chorin
,
A.
, 1968, “
Numerical Solution of Navier-Stokes Equations
,”
Math.Comput.
,
22
(
104
), p.
745
.
16.
Gerlinger
,
P.
, 2005,
Numerische Verbrennungssimulation (Numerical Combustion Simulation)
,
Springer
,
Berlin/Heidelberg
(in German).
17.
Fric
,
T.
, and
Roshko
,
A.
, 1994, “
Vortical Structure in the Wake of a Transverse Jet
,”
J. Fluid Mech.
,
279
, pp.
1
47
.