Study On The Acoustic And Aerodynamic Performance Of Semi- Active Impedance Compound Muffler

The comfort of vehicles increases gradually with the development of science and technology, and the NVH(Noise Vibration Harshness) performance becomes a research focus as a key point to make impact on the comfort of vehicles. Mufflers are important components of the exhaust system, and the performance of the muffler plays an important role in the evaluation of the exhaust system and the whole vehicle. The optimization and improvement of the acoustic and aerodynamic performance has great research value, as well as far-reaching environmental and social significance by reducing environmental pollution. The exhaust noise has broadband characteristics, and shows great variation in different bands when the working condition of the engine changes. However, the mufflers now applied are of single structure and narrow attenuation band, and show poor adaptive performance to the variation of working conditions, and therefore cannot meet the increasing demand of NVH performance.This thesis aims at the problem that the conventional 2D analysis method shows poor in solving the acoustic performance of elliptical mufflers at first, a new 3D analysis method that is suitable for the elliptical mufflers is derived by introducing elliptic cylindrical coordinates, the applicability and accuracy of the method is proved by the comparison of theoretical and experimental results. The method gets extended to multi-chambers by setting boundary conditions appropriately, and the tendency of the acoustic performance with the increase of chambers is analyzed by comparing the results of the mufflers with different chambers, the error between the calculated and measured value is analyzed, thus providing reference for the optimization of the algorithm.The acoustic performance of the impedance-compound muffler is studied based on the 3D analysis method derived above, and the structural parameters that have impact on the acoustic performance are pointed out. The effect of every parameter is studied by using the single variable method, and the tendency of resistive and resistance attenuation with the variation of the parameters are discussed, thus providing an optional direction to improve the attenuation and broaden the attenuation band.Aiming at the fact that the mufflers of single structure show poor in adapting to the varying source, a new semi-active impedance-compound structure that is able to change the output characteristic by changing the inner parameters is put forward. The output acoustic performance is measured under different sources and different inner-structure parameters, and an A-weight filtering is made to simulate the actual feeling of human ears. The results and the change regulation are analyzed and the boundary conditions of controller action is concluded by the calculation of output acoustic energy proportion to guarantee the adaption to different working conditions.A new semi-active impedance-compound structure that is able to change the airflow path by adjusting the opening of movable inner structure, and then change the acoustic and aerodynamic performance of the muffler. The acoustic and aerodynamic performance are measured through experiment when the two movable inner structures are moving synchronously and non-synchronously. The tendency of acoustic and aerodynamic performance with the variation of the two movable inner structures are concluded, and the way of adjusting the movable structures under different demands is discussed to realize the overall optimization of acoustic and aerodynamic performance.