On the iInfluence of Inlet Geometry on Turbocharger Compressor Noise.

Abstract

In today's society, there is a growing awareness of the importance of global warming. This concern is reflected by the legislative powers of Western nations in increasingly restrictive emissions regulations. In this context, the automotive industry has been strongly encouraged to develop more efficient thermal engines and even to explore new propulsion solutions, such as the electric motor.The trend adopted to improve the energy efficiency of reciprocating internal combustion engines is the reduction of engine size. This has forced compressors to work in more extreme conditions, where their acoustic emission becomes troublesome. The problem of acoustic response takes on greater relevance in the context of competition against the electric car, which is inherently quieter. Even hybrid vehicles that incorporate downsized thermal engines to power the electric motor batteries have the aforementioned compressor noise problems, which remain a disadvantage compared to fully-electric vehicles. The emergence of new technologies such as drones, whose presence is rapidly increasing in urban and industrial environments, reinforces the interest in methodologies for analyzing the acoustic emissions of turbomachines.The literature review carried out in this thesis shows that in the last two decades, there has been a great boom of research in the acoustics of radial turbocharger compressors. Despite the progress made, there is still no consensus about the cause of specific spectrum components, such as the broadband noises known as whoosh and Tip Clearance Noise (TCN). The influence of compressor inlet duct geometry on noise is also scarcely explored. This thesis presents a computational methodology of flow field analysis that allows the identification of the flow structures responsible for the most relevant spectral components and the analysis of the influence of operating conditions and inlet geometries on them.The pressure field inside the compressor is analyzed through modal decomposition techniques. These allow identifying spatial patterns and associating them to the frequencies of the measured spectrum in an objective manner. Subsequently, the flow structures corresponding to these patterns are identified, and their evolution with the operating conditions and the inlet geometry is analyzed. Through the application of the described methodology, the different mechanisms of generation of the tonal noises in the inducer and the impeller trailing edge are identified. While the former is related to the the cavern of ignorance "until finding the clarity of the sun" that represents scientific knowledge. It is certainly not an easy road, although fortunately, I have not had to travel it alone. In the first place, I owe special thanks to my supervisor, Prof. Broatch, for his support and guidance during the development of this work.Thanks to all my colleagues at the Noise and Thermal Management line, among whom I would like to express my admiration and gratitude to Dr. Jorge García-Tíscar for his always generous collaboration. I would ...