A DFT Spectrum Acoustic Analysis for Investigating Pulse Duration Effect on Performance, Psychoacoustic Sound Level of Turbocharger Turbines Through C plus plus FDM Code

The turbocharger turbine operates under high-time-fluctuating flow conditions, originated from the reciprocating motion of the engine pistons and its head valves fast closure and opening. The turbocharger turbine performance and acoustic characteristics are highly affected by the pulsating nature of the engine exhaust flow. As acoustic levels of sound usually recorded around turbocharger turbines coupled to engines is in the frequency range so heard by humans, it seems necessary to get a clear insight about its acoustic characteristics whether it contributes to the noise generation or its reduction as this work suggests. Unlike the common technique of linear acoustic characterization based on the transfer matrix theory of plane waves, the present study investigates the acoustic characteristics of one turbocharger turbine for different pulse durations of the flow using a finite difference method (FDM) gas dynamics solver developed with the C + + programming language. In this study, four pulse duration to period ratios of 25%, 50%, 75% and 100% were considered. Based on the pressure transient profiles, a nonlinear acoustic analysis relying on the short time Fourier transform (STFT) was conducted to seek out the effect of the pulse duration to period ratio on the noise generation and transmission loss of the turbine. Results revealed that the turbine plays an acoustically active and passive roles at the same time depending on the spectrum frequency. Results confirmed a significant noise reduction with a decreasing pulse duration to period ratio.