Acoustic transmission loss in turbochargers

Zusammenfassung

Internal combustion engines are increasingly being equipped with turbochargers to increase performance and reduce fuel consumption and emissions. Being part of exhaust and intake systems, the turbocharger strongly influences the orifice noise emission. Although 1D-CFD simulations are commonly used for the development of intake and exhaust systems, validated acoustic turbocharger models are not yet state-of-the-art. Additionally, there are only few literature sources on the acoustic influence of the turbocharger. Consequently, the aim is the investigation of the influence on the orifice noise and the development of an accurate model for 1D-CFD simulations.

Therefore the acoustic transmission loss was measured for a wide operating range of four turbochargers, including wastegate and VTG-system variations. The applications range from small gasoline engines up to large diesel engines. These investigations reveal that low frequencies for compressors and turbines are dominated by impedance discontinuities, while the upstream transmission loss increases considerably with high mass flows and pressure ratios. Especially for the compressor, high frequencies are determined by destructive interference in the stator. Overall, the turbocharger has a high damping potential.

While Aymann’s common simulation approach accurately captures low frequencies, a new generic approach was developed to additionally model high-frequency interferences by linking the stator geometry with potential sources and turbocharger performance maps. In this way, high acoustic and thermodynamic prediction quality could be achieved. This could be proven especially for higher frequencies of the intake orifice noise, where the predicted sound pressure level was corrected by up to 5 dB.

The presented newly developed model for 1D-CFD simulations increases the efficiency of the acoustic development process of intake and exhaust systems. The applied measurement approach has great potential to further improve also the model development process of other intake and exhaust system components.