Study On The Simulation Technique Of Engine Exhaust Silencing System

The exhaust systems play the important role of controlling the engine exhaust noise, so it is necessary to simulate and analyse the characteristics of the exhaust system. In the past, the acoustic analysis was carried out under the hypothesis of ideal fluid, but the visco-thermal effect can attenuate the sound in the actual fluid. So the acoustic characteristics of exhaust system should be analyzed under the consideration of the visco-thermal effect on the sound propagation.Based on the pseudo-plane-wave theory which takes the visco-thermal effect into account, the sound attenuation cased by the visco-thermal effect is analyzed in this paper, and the influences of temperature, flow velocity and duct dimensions on the sound attenuation are studied. At the same time, a hybrid numerical and analytical method is used to calculate and analyse the visco-thermal effect on the sound propagation in wider ducts.Based on the pseudo-wave theory, the transfer matrices of acoustic elements are obtained, and the formulas of acoustic characteristics of engine exhaust system are obtained with the method of transfer matrix. Then a quick visual program is developed for the analysis of acoustic characteristics and fluid resistance of the engine exhaust system. The analysis of fluid resistance is based on the empirical formulas. Comparisons of predicted and experimental results illustrated that the acoustic results are accurate below the cut-off frequency, and the program can analyse the influence of thermal viscosity, temperature and flow velocity on the sound propagation. The program may be used to predict the fluid resistance, however the...