【作者】 陶丽芳；

【导师】 胡玉梅；

【作者基本信息】 重庆大学 ， 车辆工程， 2005， 硕士

【摘要】 设计高消声性能、低压力损失的排气系统是目前汽车噪声控制中的重要课题。传统的排气系统内消声器设计主要根据一维平面波理论,但该理论难以正确模拟三维波动效应等实际因素的影响,计算结果不准确。而有限元等三维数值方法在对排气系统性能进行准确模拟的同时还能考虑到多种外界因素的影响,是排气系统性能预测和改进设计的有效方法。本文研究了基本消声结构的消声特性和消声规律,在此基础上对某发动机排气系统进行了流动特性和消声特性的三维数值模拟。通过流动特性分析得到了系统内流速、温度和压力的分布情况。结果表明:由于内插管和穿孔管的存在,排气系统中前、后消声器内压力损失较大,各腔内流速变化也很复杂,温度分布虽然比较均匀,但各腔之间的温差大,这些都会对消声性能产生一定的影响。采用有限元方法,在对穿孔隔板、穿孔管和吸声材料进行精确建模,并考虑温度、流速和尾管反射对消声的影响的基础上,对消声特性进行分析。结果表明:排气系统的低频和高频消声效果不好,消声量明显不足。但温度的升高,使消声频谱往高频移动,使得高频消声效果变好,中低频变差;而尾管反射对低频消声有改善作用;流速会使消声量有所减小。可见对排气系统进行消声性能分析和改进设计时不能忽视这些外在因素的影响。为改善排气系统的空气动力特性和低频、高频的消声特性,在对前、后消声器各消声单元消声特性深入研究的基础上,对消声器芯部结构进行了改进设计。改进后的流场和声场分析结果表明:改进设计使得排气系统的空气动力特性、低频、高频消声特性等方面都较原结构有所改善,达到了预期改进目标。文中对排气系统的数值模拟不仅可以为试验提供有力的指导,而且也积累了一定的改进经验和改进方法,是今后消声系统改进设计的重要参考。总之本文为发动机排气系统的性能预测和改进设计探索了一种比较有效的现代设计方法。更多还原

【Abstract】 It is an important topic to design exhaust mufflers that have good attenuation performance and low pressure loss in the field of automobile’s noise control. Most of the exhaust system design methods developed earlier have dealt primarily with one-dimension-plane wave theory. But the theory is hard to provide accurate analysis result because of the effect of the three dimensional wave and some other actual factors. The three dimension numerical method such as the finite element method can simulate the exhaust system’s characteristic accurately and take the influence of several outside factors into account. So it is an effective method to predict exhaust system’s performance and have an improved design. The flow and attenuation performance of an engine’s exhaust system is simulated applying the three dimension numerical method, which is basing on the studying of the attenuation performance and rules of basic muffler elements Distribution of velocity, temperature and pressure in the muffler is achieved by analyzing the flow performance. The results indicate that: Pressure loss in the muffler is high and velocity in every chamber change complexly. Though temperature distributes equably, the difference between every chamber is large. All these could have effect on the attenuation performance. The finite element method is applied to analyze the attenuation performance, which is basing on that porous clapboard, porous pipes and absorbent are accurately modeled and the influence of temperature, velocity and tail reflection is taken into account. The results indicate that: Attenuation performance of the exhaust system in low and high frequencies isn’t good and the magnitude is obvious insufficient. But when temperature rises, the spectrum moves toward higher frequency, which makes the attenuation performance in high frequencies better and that in middle frequencies worse. Tail pipe’s reflection has good effect on the attenuation performance in low frequencies. The flow of air reduces the attenuation. As a result, these outside factors can’t be ignored when analyzing the attenuation performance and redesigning the exhaust system. In order to improve the original exhaust system’s aerodynamic quality and attenuation performance in low and high frequencies, the inside structure is primarily redesigned after studying the attenuation performance of every muffler element. We can see from the numerical results of the improved exhaust system in acoustic and fluid fields that: the improved design succeeds in increasing the attenuation performance and reducing the pressure loss and meliorating the aerodynamic quality. The numerical simulation in this paper can provide powerful guidance for the test. What’s more, some improved experiences and improved methods are accumulated, which will be the important reference for the redesign of exhaust system in future. In conclusion, a new modern design method for the characteristic’s prediction and redesign of the engine’s exhaust system is developed in this paper.更多还原