PhD Defense – Mélissa FERAND : “Numerical modeling of far-field turbofan-engine combustion noise”
Since the introduction of jet engine for aircraft propulsion in the 1950’s, acoustics has become of great interest to the engine industry. While the initial turbojets were jet noise dominated, the introduction of turbofan engine in the 1960’s gave relief in jet noise, but introduced fan noise. In the 1970’s, with advanced noise reduction design features which provided a major reduction in aircraft noise, combustion noise became an interrogation. Indeed, more restrictive noise regulations could require that noise from the fan and jet be reduced to the point where combustion noise reduction may be required. Moreover, burner designs is controlled solely by the restriction of chemical pollutants produced by combustion, efficiency and consumption. The impact of these new concepts on combustion noise is not a strong constraint for design.
Before considering to reduce combustion noise, it is necessary to first understand the different mechanisms. However, proposing a prediction method for combustion noise is not an easy task due to the multiple physical interactions involved during the combustion processes. Many experiments exist to evaluate the combustion noise from flames or combustion test rig. However, only a few include the complete propagation path of combustion noise within an engine device as it is difficult to isolate this acoustic source from the noise of the other engine modules. Empirical methods based on extrapolations and simplifications are often used for the prediction of combustion noise within modern aero-engines. Numerous acoustic analogies have also been derived from Lighthill.
The work of this thesis proposes to study the combustion noise coming from an aircraft engine using a computational chain treating different modules from the generation of combustion noise to its propagation in far field. The importance of combustion noise for different operating points is highlighted. The noise-generating mechanisms will be identified in the combustion chamber. The role of the turbine as a noise attenuator and indirect noise generator will be evaluated as well as the far-field propagation considering inhomogeneous fields.
Finally, an alternative strategy will also be proposed in order to consider the interaction between combustion noise and jet noise. To do so, LES of jet flow forced with combustion noise will be performed. A new approach will be proposed based on these results which seem to show that the combustion noise has an impact on the turbulence of the jet.
Françoise BAILLOT Professor, CORIA CNRS, Rouen Referee
Christophe BAILLY Professor, Ecole Centrale de Lyon Referee
Alexis GIAUQUE Professor, Ecole Centrale de Lyon Member
Guillaume DAVILLER Researcher, CERFACS Toulouse Member
Claude SENSIAU Engineer, Safran Aircraft Engines Industrial invited
Thierry POINSOT Research Director, IMFT CNRS, Toulouse Advisor
Stéphane MOREAU Professor, Université Sherbrooke, Canada Co-advisor