Turbochargers are nowadays, with the emerging technology of downsized combustion engines, an essential part of automotive engines. The demand of full boost pressure at low engine speeds while avoiding over boosting at high engine speeds constitutes boost pressure control systems such as multi-stage boosting systems (e.g. Regulated Two-Stage System) an important part of turbocharged engines. These systems contain integrated controlling valves in order to function correctly. A good example for the regulating feature in Regulated Two-Stage System (R2S) systems is an integrated recirculation valve in the compressor housing (CRV). This comes with various NVH issues, since the recirculation process and the piping of such valves can be the root cause of such acoustic problems. The aim of this paper is to conduct an acoustical comparison between three different CRV designs as a part of centrifugal compressor stage. Aim is to find a compromise in terms of aero-acoustics and performance. The method used is in this paper is a hybrid Computational Aero Acoustics calculation (CAA) consisting of Unsteady Reynolds Averaged Navier Stokes (URANS) accompanied by the acoustic evaluation. Firstly, the fluid dynamical behavior of the compressor stage containing CRV is calculated with the help of Computational Fluid Dynamics (CFD) followed by calculating the noise sources on the basis of acoustic analogies. Additional investigations are conducted based on the system’s cavity resonances that could aggravate the associated acoustics. The simulation results reveal a clear acoustical dependency of the CRV volume and the shape of the connecting pipes. There is a specific design tendency for both the CRV chamber volume and the piping depicting a positive acoustic response. This tendency relays on the functionality of the recirculation in the compressor stage, which helps to regulate the pressure ratio. These patterns are also identified and confirmed by measurements.
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