Acoustic Analysis Of ICE Intake And Exhaust Systems By A3D Time-domain Pulse Method

The acoustic characteristics of intake and exhaust systems, as important components of the ICE (internal combustion engine), are key factors to determine the intake and exhaust noise value. The acoustic properties of the intake and the exhaust systems are not only associated with their structure, but also influenced by the airflow there through. Frequency-domain and time-domain methods are adopted to analyze the acoustic properties. The former has limitations in analyzing the acoustic effects of the airflow, while the time-domain methods, especially the3D CFD (Three-dimensional Computational Fluid Dynamics) method, are adequate to directly calculating the acoustic properties of the system considering the mean flow effect.In this dissertation, a3D time-domain pulse (TDP) method, which was theoretically based on CFD, by inputting a pulse as sound source, by means of analyzing time-domain fluctuations at the inlet and outlet and fairly using non-reficetive and reflective boundaries, was proposed in order to solve acoustic properties of flow-duct system, i.e. TL (Transmission Loss), NR (Noise Reduction), four-pole matrix, etc. Under the conditions of without and with mean flow, issues were studied related to the3D TDP method, which included boundary setup, solver setup, simulation of the flangless open end, load of the flow-field and temperature-field, setups of the turbulent model, the grid model, and so on. The outlet was set as non-reflective boundary in calculating TL, and the flangeless open end was simulated either by the correction pipe method or by the direct modeling method, while calculating NR. With the results obtained by various methods, the influence of the intake and the exhaust flow on the acoustic properties was analyzed. The3D TDP method of calculating the silencer four-pole matrices including scattering matrix and transfer matrix was studied. Combined with the frequency-domain acoustic characteristics of the intake or the exhaust port, the NR and impedance of silencers could be obtained considering the mean-flow effects. The matrix method has solved the inaccuracy problem of the3D TDP method directly simulating the acoustic character of intake and exhaust ports. As known, intake and exhaust systems often contain a porous sound-absorbing material, such as filter element in the intake air-cleaner and glass fiber in the exhaust muffler. A method based on value fitting between simulated and measured results was proposed to obtain the acoustic parameters of the porous material. Emphasis was made on the3D TDP method of simulating porous material, and features of the acoustic finite element method and the3D TDP method was discussed, based on the comparison of the calculated results to the measured ones.The3D TDP method was utilized to fulfill three engineering projects. First, the method was adopted to predict the acoustic performance of the compressor outlet silencer in the influence of high speed flow. According to the compressor outlet noise measurement, the noise attenuation at high frequencies of the silencer was evaluated. Further, the silencer was acoustically optimized to improve its acoustic performance. Second, the3D TDP method was used to calculate the transfer matrix of the exhaust muffler with high-temperature flow. The TL and NR of the muffler were obtained, and it was found that within600Hz, the performance of the muffler decreased with increasing Mach number and temperature. Besides, the exhaust noise was predicted based on the acoustical source obtained by the multi-load least-squares method and the transfer matrix of the exhaust system calculated by the TDP approach. Accepted bias existed within600Hz between the calculated result and the measured one, and values of the2nd,4th,6th,8th order were in good agreement. Third, the intake noise was predicted based on the acoustical source and acoustic properties of the intake system calculated by the TDP method. It was compared with the measurement, in order to analyze the error causes and guide improvement. The intake system was acoustically optimized for reducing the prominent parts of the intake noise. Afterwards, NR and intake noise were calculated, and vehicle stationary and road tests were conducted to measure the intake noise and the vehicle interior noise. According to the calculated and the measured results, it was found that the variation of the calculated results before and after optimization matches well with the measured results, and the optimized intake system achieved the engineering purposes of reducing the intake noise.