Optimizing the acoustic performance of turbochargers

Turbocharger usage is predicted to increase in passenger vehicles for reasons such as enabling engine downsizing and improving thermodynamic efficiency. In order to achieve customer expectations, the acoustic performance of the turbo needs to be engineered for a wide range of operating load conditions. This requires the turbo supplier to set component targets in CAE and identify undesirable noises early in the development process using test cell acoustic measurements. Noise from a turbocharger can be separated into two main categories: (1) aeroacoustic sources including blade pass, pulsation, surge and broadband flow noise (2) structureborne from vibration sources such as subsynchronous, first order imbalance, and component resonances. One technique for comparing compressor acoustic performance is noise mapping, where the in duct noise data are collected across the full turbo operating range and post processed into 3D plots. Audible noises that can be generated in a centrifugal turbocharger and methods of identifying sources during development are presented in detail.