Internal Flow Field Simulation Of Passenger Car Exhaust System Cold End And Prediction Of Muffler Airflow Regenerated Noise

As the number of vehicles increases sharply in cities, air pollution and sound pollution are getting worse, requires more attention. National governments carry out stricter and stricter emission regulation. Vehicle manufactures commit themselves to reduce emission and noise of vehicles. Consumers are more and more apt to choose comfortable, economical and less pollution vehicles. Exhaust system is a general approach to reduce air pollution and sound pollution caused by vehicles.In the automotive exhaust system design process, the designers should focus on its anechoic performance, aerodynamic performance and gas flow regenerated noise. In this paper, the 3D flow field of a certain passenger car's exhaust system end design scheme was simulated by the CFD software FLUENT. Based on the analysis of back pressure, velocity field, pressure field and turbulence energy field, combined muffler related theories, aimed at the back pressure, gave advices for the structure improvement, and then made CFD simulation for the improved scheme.Did real machine experiments for both original scheme and improved scheme, verified that under the premise of meeting anechoic performance the back pressure reduced effectively, and the test result was identical to simulation results, also verified that the computational method used in FLUENT in this paper was of high accuracy.When airflow flows in mufflers, on the one hand, it causes vortex because of local drag and friction force and generates sound, on the other hand, the vortex pressure pulsation excites mufflers'internals vibration and generates sound, the two kinds of sound make up mufflers'airflow regenerated noise. When the airflow regenerated noise up to a certain extent, is will reduce mufflers'real noise reduction, even makes mufflers become loudspeakers, so attention should pay to airflow regenerated noise in muffler design. The airflow noise generated by vortex is the main composition of the airflow regenerated noise, this paper tried to predict the airflow noise in the mufflers. The software FLUENT has three sorts of aeroacoustics computing model. This paper used the broadband noise source model, the Ffowcs Williams and Hawkings model and direct method to try to predict airflow noise in mufflers. The study showed that all the three methods can be used to predict airflow noise in mufflers in a way, but the three methods had limitation. So this paper discussed the three methods'applicability and advantages and shortcomings, provided a reference for the mufflers airflow regenerated noise prediction.