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

2 Combustion
The research activity of the combustion team at CERFACS is continuously adapting to face new challenges,
and is now structured in three main domains : (1) fundamentals of turbulent combustion remain an important
topic to continue to improve simulation capabilities for gas turbines, rocket engines and piston engines ;
other phenomena exist in such burners, such as (2) acoustics and combustion instabilities, which are another
major subject, and (3) heat transfer, and more generally multi-physics, is becoming also an important
topic. Such simulations require highly efficient and accurate numerical and computational methods, a
central and crucial topic for the team, and imply to test solvers on all computational platforms. Multiphysics
add a new dimension to parallel computing, as it includes the simultaneous coupling of different
solvers. Target applications remain mainly in the domain of transportation (aircrafts, helicopters, rockets and
piston engines), and has been recently extended to furnaces and explosion under the impulse of CERFACS
shareholder TOTAL.
2.1 Turbulent Combustion
2.1.1 Chemistry (B. Franzelli, E. Riber, B. Cuenot, T. Poinsot)
A growing need for simulations based on reliable chemistries has been underlined in the last years to
improve the prediction of flame-turbulence interactions as well as pollutant emissions. Two approaches
have been proposed to overcome this problem. On the one hand, reduced chemistry consists in simplifying
a detailed mechanism to obtain the main features (flame structure and species concentrations) using fewer
species and reactions. CERFACS has developed a methodology to build two-step mechanisms valid over
a wide range of pressure, temperature and equivalence ratio. It has been applied to kerosene-air flames
[CFD70] and methane-air flames [CFD33]. These reduced schemes are systematically tested in academic
laminar configurations (freely propagating premixed flames and strained premixed counterflow flames) to
anticipate their behavior in three-dimensional turbulent configurations. The methodology has been tested
for methane-air flames, comparing five reduced mechanisms from a two-step scheme to a more complex
scheme comprising 13 resolved species and 73 elementary reactions [CFD90, CFD178]. On the other
hand, tabulated chemistry is a promising technique based on the idea that tabulated information from
academic laminar flames may be used for turbulent calculations. This method is still difficult to handle
when heat losses, dilution by recirculating gases or several streams feeding combustion must be accounted
for. CERFACS collaborates with IFPEN, CORIA and EM2C to develop tabulation methods in AVBP and
apply them to complex geometries [CFD25].
2.1.2 Pollutant emissions (G. Lecocq, I. Hernandez, D. Poitou, E. Riber, B. Cuenot)
In parallel to chemistry modelling, CERFACS has started to develop soot models. Soot particles contribute
to the thermal balance of a combustion chamber and can notably affect the burnt gas temperature seen by
the turbine blades [CFD1]. At a larger scale, soot particles are suspected to trigger contrail formation in
the wake of planes during cruise flight. Such contrails may modifiy the cloud coverage and, through altered
radiative balance, affect the local climate. Soot is the product of complex processes, starting by nucleation
(formation of the first particles) that occurs through collision of polycyclic aromatic hydrocarbons (PAHs),
CERFACS ACTIVITY REPORT 131