On the Measurement and Simulation of Flow-Acoustic Sound Propagation in Turbochargers 2019-01-1488
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. Consequently, the first aim of the paper is the investigation of the influence on the orifice noise and the development of an accurate 1D-CFD model.
Firstly, active and passive acoustics of turbochargers are distinguished. Complex active turbocharger noise emissions were investigated on a turbocharger test rig and could be correlated with unstable rotating stall. Therefore critical acoustic operation can be identified in early engine development stages by comparison to other tested turbochargers.
The passive acoustic transmission loss was measured for a wide operating range of four turbochargers, including wastegate and VTG-system variations. Low frequency attenuation is dominated by impedance discontinuities, increasing considerably with mass flow and pressure ratio. High frequencies are determined by destructive interference in the stator.
A new generic turbocharger model was developed to model both low frequency impedance discontinuities and high-frequency interferences by linking an idealized stator geometry with potential sources and turbocharger performance maps. In this way, high acoustic and thermodynamic accuracy could be achieved. The model was validated and significant improvement could be identified especially for higher frequencies of the intake orifice noise, where the predicted sound pressure level was corrected by up to 5 dB.
Lastly, gasoline particulate filters are continuously introduced in passenger cars. Following a detailed component model development process with transmission loss measurements, an exhaust system integration study was performed. It was concluded, that the gasoline particulate filter can replace absorption mufflers, while still fulfilling tail pipe noise emission and partly the backpressure targets. The advanced transmission loss measurement approach holds great potential to further improve intake and exhaust system development processes.
Hendrik Ruppert, Felix Falke, Stefan Pischinger, Marco Günther, Ralf Stienen
Institute for Combustion Engines, RWTH Aachen University, FEV Europe GmbH
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