Simulation of Radial Compressor Aeroacoustics Using CFD

Abstract

This paper focuses on the application of CFD to the prediction of radial compressor aeroacoustics. It concentrates mainly on automotive turbocharger operations in the low mass-flow range where blade leading-edge and tip separation reduce the compressor performance and induce transient flow behaviour. Whereas the blade-passing is tonal and at high frequency, usually beyond the human hearing range, transience in the flow are turbulence-dominated, broad-band in nature, and in magnitude a significant source of aeroacoustics which appears well within the range of peak human hearing (1–5kHz). Other noise sources occur due to distortions in the flow upstream of the compressor face, and rotating stall. The simulation methodology enumerated here pays attention to all the above flow-induced aeroacoustics. Due consideration is given to turbulence modelling, to ensure that both the narrow-band and broad-band sources are directly resolved in the CFD. Appropriate discretisation practices are adopted, so as to capture both turbulent-convection and sound-propagation mechanisms. Pressure-wave non-reflective boundary conditions are applied to the computational boundaries to remove any artificial resonances in the domain. STAR-CCM+, the commercial CFD code used here, was previously benchmarked against experimental data for the same compressor under ideal installation conditions, then the compressor performance assessed under real installation conditions [1]. The main foci of the studies reported here are to exploit possible improvements in modelling of the device performance and efficiency curves using more detailed wall modelling, comparing low-y+ versus high-y+ wall resolution, and to explore the viability for transient CFD calculations to capture the noise sources in the compressor at the challenging low mass flow end of the performance characteristic.