CERFACS CERFACS Scientific Activity Report Jan. 2010 – Dec. 2011

COMBUSTION
chambers and theoretically of CI. This is an attractive method made possible by recent progress in HPC
technologies on machines using 10 000 to 300 000 processors and demonstrated by various groups in the
last years, many of them using the AVBP code developed at CERFACS [23, 27].
(2) Thermo-Acoustic (TA) codes coupled to forced response LES : in most CIs, acoustics are the dominant
resonant mechanism and a proper method to decompose the physics of CIs is to use TA codes which can
track the propagation of waves in the combustor. In this approach, the mean flow is frozen and the solver
only tracks the acoustic modes of the system. The flames are replaced by active components (which can
be compared to complex loud speakers). If the action of these active elements is properly represented, the
global stability of the combustor can be predicted.
Both methods are required to understand CIs. A major interest of TA codes is to isolate the elements leading
to CIs into different blocks (something a brute force LES cannot do) : a) the acoustics of the combustor, b)
the outlets and inlets impedances and c) the response of the flame which is quantified by a function called
the Flame Transfer Function (FTF) describing how much unsteady heat release is produced by a flame when
it is submitted to an acoustic velocity fluctuation.
2.2.1 Combustion noise (M. Leyko, I. Duran, C. Silva, C. Lapeyre, T. Livebardon,
F. Nicoud, S. Moureau)
The noise generated by unsteady combustion in a gas turbine is becoming a significant source for aircraft
and helicopter engines. CERFACS is studying combustion noise with SNECMA (PhD of M. Leyko and I.
Duran), TURBOMECA (PhD of T. Livebardon) and through national or European projects like BRUCO,
DISCERN or ECCOMET (PhD of C. Silva and C. Lapeyre). This work is performed in close collaboration
with Pr. Nicoud (Montpellier) and Pr. Moreau (Un. Sherbrooke, Canada). Evaluating the noise generated
by combustion in a gas turbine requires to compute the noise sources (due to unsteady combustion) but also
their propagation through the turbine stages. For the generation, CERFACS performs LES of combustion
chambers. For propagation, CERFACS analyzes the waves leaving the combustor outlet in the LES and
computes their transmission and reflection through the turbine stages using the compact nozzle analytical
theory [17, CFD99] proposed initially by Marble and Candel [18] and extended by Cumpsty and Marble [5].
In 2012, these methods will be applied to two new combustors : a lab-scale burner installed at EM2C Paris
(DISCERN) and a full helicopter engine at TURBOMECA instrumented in the European TEENI project.
2.2.2 Brute force LES of combustion instabilities (I. Hernandez, S . Hermeth,
P. Wolf, G. Staffelbach, T. Poinsot)
CERFACS explores brute force LES of combustion instabilities (CIs) in different configurations : in
laboratory burners during the LIMOUSINE Marie Curie project, I. Hernandez performed an LES of selfexcited
oscillation modes in a lab-scale combustor installed at U. Twente and showed that LES was able
to capture the first two unstable modes observed experimentally and to predict that these modes would
disappear when the equivalence ratio would decrease. S. Hermeth, working in the MYPLANET Marie
Curie project, studied the forced response of another lab-scale combustor installed at TU Berlin before
simulating one sector of a real industrial burner for the Ansaldo company. Finally, P. Wolf (PhD for
TURBOMECA) has performed the largest LES ever done for combustion in a 360 degrees combustion
chamber. This work initiated during the 2010 Summer Program of CTR at Stanford has lead to various
publications [CFD64, CFD110], providing new insights into the nature of the azimuthal turning or standing
modes in full annular chambers. For all these brute force LES, companion simulations using acoustic solvers
(TA codes, see Section 2.2.3) have been performed to compare the output of the TA code to the LES data. A
workshop organized at CERFACS on Nov. 22, 2011 with most European experts (Alstom, Siemens, Safran,
138 Jan. 2010 – Dec. 2011