Numerical Simulation of Turbulence Induced Flow Noise in Automotive Exhaust Systems Using Scale-Resolving Turbulence Models

As a first step for a general numerical method for exhaust noise prediction a simplified generic exhaust system model, the straight pipe, has been investigated in terms of turbulence induced flow noise. Impinged with a constant mass flow rate, the dominant acoustic source mechanism was reduced to the subsonic jet behind the orifice at a Mach number of \(\text {M}_{\text {j}}=0.3\). In order to calculate the radiated jet noise, detached eddy simulations have been carried out to receive transient data of the turbulent flow field. Afterwards these data were used for the calculation of the acoustic far-field, based on the Ffowcs Williams-Hawkings acoustic analogy. Additionally experimental investigations of the turbulent flow as well as the acoustic far-field have been carried out in order to validate the numerical results. The acoustic results offered a good prediction of the sound pressure level at high frequencies compared to experimental data. Otherwise partially high deviations were depicted in the lower frequency range. The study of the turbulent flow field showed, that the delay of the development of turbulent structures at the jet beginning, caused by the absence of initial turbulent fluctuations, is a possible reason for this overestimation. Due to these dominant low-frequency components, the overall sound pressure level also offered an overestimation, but a good prediction of the directivity of the sound pressure field.