Design and Optimization of New Metallic Materials (Metal Foams) for the Reduction of the Noise of the Aeronautical Turbo Engines

The need to control noise generated by aircraft has become a major concern for the aeronautic community (industry as well as civil and military authorities). In order to reduce engine noise, there are two possible approaches: either the reduction in the generation of the noise or the increase in the capacities for absorption of the noise generated. The first approach consists in optimizing the geometry of the exhaust nozzle, an approach which will quickly result in trying to optimally balance performance of an engine and the extent of noise reduction (reduction of the velocity and temperature of the reaction jet gases and increased dispersion of the jet). The present project has explored the second strategy - noise absorption. The main purpose of this project was to propose a new type of material architecture (microstructure) usable in manufacturing exhaust nozzles with good acoustic absorption capacities by maintaining their overall weight and high temperature mechanical performance. Since the requirements for thermal loadings are more stringent at the exhaust nozzle level than the mechanical loadings, metal foams appear to be the most appropriate material system for noise reduction. Finding the best solution in terms of balancing structural strength and acoustic properties was the main thrust of this project. Acoustic phenomena such as absorption, reflection and transmission, and mechanics of Hollow Spheres-based cellular materials were studied and the understanding gained thus far will help engineers design optimized exhaust nozzles of turbo-engines (high-level loading conditions under pressure and temperature). A method of optimized design was also proposed and tested on a specific study case. The present project was conducted using a multidisciplinary approach; knowledge in solid mechanics, acoustics, fluid mechanics and metallurgy were all required. The original document contains color images.