Turbocharger Compressor Noise: a Numerical Study

Sammanfattning: Road transport is the primary means of conveyance of passengers and freight in the EU, accounting for 71% and 52% of the totals, respectively. At low speeds and in situations with frequent start-stops and accelerations, i.e., typical in downtowns and residential areas, the noise from the turbocharger compressor becomes a distinctive source of noise and an important contributor to road transport noise, affecting human health and wildlife, both inside and outside urban areas. To reach quieter operation, the reduction of the aerodynamic noise sources must be addressed; by investigating the noise mechanisms, it is possible to develop noise reduction technologies.The thesis' aim is to be a systematic numerical study of the aerodynamically generated noise in turbocharger compressors. Several simulation techniques were employed in the search for a thorough understanding of the acoustic behaviour of such machines, spanning from the steady state Reynolds averaged Navier Stokes (RANS) with a quick turnaround to the scale-resolving detached eddy simulation (DES), allowing to retrieve information about the acoustic field by means of turbulence predictions and the direct noise computation (DNC) approach. The acoustic results, only describing source information thanks to the non-reflecting boundary conditions developed as part of the work, were verified against experimental data with satisfactory match. On data from such setups, decomposition techniques based on the momentum potential theory (MPT) and the dynamic mode decomposition (DMD) were implemented to gain further insight into the noise generation mechanisms and the locations of the fluctuations of main interest.The study is a valuable base on which to develop further aerodynamic noise source investigations within rotating machines.