【作者】 范钱旺；

【导师】 沈颖刚；

【作者基本信息】 昆明理工大学 ， 动力机械及工程， 2007， 硕士

【摘要】 排气噪声是汽车及其内燃机的主要噪声源之一,在内燃机整机噪声中,排气噪声往往比其它噪声高出10～15dB(A)左右。目前国内外减少排气噪声最有效、最直接的方法是安装排气消声器。因此,研究排气消声器消声性能对消声器的改进设计以及降低排气噪声有着重要的意义。本文总结推导了消声器声学基本元件的传递矩阵。基于传递矩阵法计算分析了简单扩张式和内插管扩张式消声器的结构参数对消声器消声性能的影响规律;计算分析亥姆霍兹共振和穿孔管共振消声器的结构参数对消声性能的影响规律;计算分析气流速度和温度对消声器消声效果的影响。仿真结果表明:气流速度小于35m/s左右时,气流速度对消声器的消声性能影响不大;当气流速度大于35m/s左右时,随气流速度增大消声量急剧下降。此外,不同的结构参数对消声性能也有重要的影响。为了进一步研究消声器内部声场特性,基于有限元法,以单扩张式消声器和亥姆霍兹共振消声器为例,运用Sysnoise声学软件建立FEM—Fluid三维模型。对比分析了单扩张式消声器在有、无气流存在时的传递损失以及基于传递矩阵的一维模型和三维有限元模型的计算结果;仿真计算两种消声器内部压力分布、速度分布情况,分析了消声器内部声场特性。结果表明,频率在1500Hz以下,一维和三维模型计算结果基本吻合,而在其它频率段,两种模型计算结果偏差较大。根据实测的四缸柴油机在标定转速下有、无原消声器的排气噪声频谱图分析,原消声器在频率100Hz～500Hz范围内需要优化。基于传递矩阵法提出四种改进设计方案,考虑到经济性、加工的可行性,选取方案3和方案4进行加工。试验结果表明:在频率大约低于400Hz时,安装方案3改进的消声器比安装方案4改进的消声器,排气噪声平均降低3 dB(A)左右;比安装原消声器,排气噪声平均降低7dB(A)左右。试验结果也表明基于传递据阵法建立的减小低频率段噪声的数学模型是可行性的,对消声器设计有着重要的指导意义。更多还原

【Abstract】 The exhaust noise is the most main noise source of automobile and even its internal combustion engine, often is about 10 ~ 15dB (A) higher than entire noise of the internal combustion engine in which exhaust noise isn’t included. At present, it is the most effective and direct method to install the exhaust silencer to reduce the exhaust noise.Therefore, the researched exhaust silencer have the vital significance to reduce the exhaust noise .The present paper, summarized and infered transition matrix of acoustic primary element of silencer.By method of transition matrix, computed and analyzed effect of structure paremeter in the simple expansion type silencer and insert tube expansion type silencer to acoustic performance; Computed and analysed effect of designed parameter in Helmholtz wave resonating silencer and perforated pipe resonating silencer to noise elimination performance; Computed and analysed stream velocity and temperature’effect to noise elimination performance. The analysed conclusions show: When the stream velocity is smaller than about 35m/s, the stream velocity is not big effect to noise elimination performance; When the stream velocity is bigger than about 35m/s, along with the stream velocity increasing noise elimination performance suddenly drop. In addition, the different design parameter has the important influence to the noise elimination performance as well.Further, in order to study the silencer’performance, based on the finite element method. taking the simple expansion type silencer and Helmholtz wave resonating silencer as example, built three-dimension models of FEM—Fluid with the Sysnoise acoustic software. contrasted and analysed the transmission loss of silencer with or without air current existence; and contrasted the computed results of one-dimension model based on transmission matrix method and three-dimension finite element model. Simulated and computed internal pressure distribution and velocity distribution in silencer,and studied interior sound field characteristic of silencer. The results indicate, the silencer below 1500Hz, computed result of one-dimension model and three-dimension model is nearly consistent, but during other frequency bands, both of models are more inconsistent.According to tested noise result of four- Cylinder diesel with or without original silencer, when it run at the demarcated rotational speed, between 100Hz and 500Hz frequency scopes, original silencer is still improved. According to the transmission matrix technique, proposed four kind of improved design proposals, while considered economical factors and processing feasibility. In the end,selected plan 3 and plan 4 and processed. the test results indicate: under about 400Hz frequency, noise of improved silencer by plan 3 is about 3 dB (A) lower than improved silencer by plan 4, about 7 dB (A)lower than original silencer’s. The test results also indicate, by method of transition matrix, established the mathematical model to reduce noise is feasible, and there is the important instruction significance to the silencer design.更多还原