汽车消声器性能分析与设计_毕业论文

毕业设计论文

汽车消声器性能分析与设计

摘要

消声器作为控制排气噪声的一种简单而有效的方法，在汽车发动机排气系统中得到了广泛的应用。设计高消声性能、低压力损失的排气消声器是目前汽车噪声控制中的重要课题。本文针对某典型发动机排气系统设计了一款消声器，并对其进行了分析和改进。

本文利用声场有限元方法和流场有限容积方法分析了简单扩张腔的声场、流场分布规律，探讨了气流对消声器性能的影响，结果表明：随着温度的升高，传声损失频谱往高频移动，使得高频消声效果变好，中低频变差；。可见对排气消声器进行设计、分析和改进时不能忽视这些外在因素的影响。

根据发动机排气直管噪声频谱特性，设计了一款排气消声器，在此基础上建立实体模型和有限元模型，仿真分析了内部多物理场分布，总结了该消声器的声学特性和空气动力性。结果表明：该消声器在20~100Hz、800~1200Hz 及600~2000Hz低、中频段的传声损失偏低，高速气流可能导致再生噪声较大，压力损失较大，各腔温度差异大。

关键词：排气消声器；有限元；空气动力性；声学特性

Performance Analysis and Design of Car Muffler

ABSTRACT

As a effective method of controlling vehicles noise, muffler has been widely applied in exhaust system of engine. It is an important topic to exhaust mufflers that have good attenuation performance and low pressure loss in the field of automobile’s noise control. A muffler for a typical exhaust system is designed. The finite element method is applied to simulate it characteristic and to predict it performance so as to have an improved design.

The finite element method is applied to analyze the rules of the flow field, and acoustic field inside expansion chambers which is basing on that the influence of temperature and velocity is taken into account. The results indicate that: When temperature rises, the spectrum moves toward higher frequency, which makes the attenuation performance in high frequencies better and that in middle frequencies worse. When the temperature and heat transfer, the velocity of turbulence is rise，and pressure loss is reduced .As a result, these outside factors can’t be ignored when designing, analyzing and redesigning an exhaust muffler.

An exhaust muffler is designed basing on analyzing the sound of the engine. By building a model of it, different grid meshes are formed based on the calculation characteristic of acoustic field and the flow field. The acoustics and aerodynamics performance of the muffler are analyzed. The result suggests that the sound attenuation pat 20~100Hz,800~1200Hz and 1600~2000Hz frequency isn’t good , the high-speed flow may bring the air flow regeneration noise ，the pressure loss is little of high and the difference between every chamber is large.

Key words：Exhaust Muffler, Finite Element Method, aerodynamics

performance, Attenuation Performance

目录

前言 (1)

第1章绪论 (2)

1.1 消声器国内外研究现状 (2)

1.2 本课题的主要研究目的与内容 (2)

第2章消声器理论基础 (3)

2.1 声压 (3)

2.2 声阻抗 (4)

2.3声功率和声强 (4)

2.4 级的概念 (4)

2.5理想流体媒质中的声波方程 (5)

2.6消声器性能的评价指标 (6)

2.6.1消声量 (6)

2.6.2消声频率范围 (7)

2.6.3阻力损失 (7)

2.7消声器的分类 (7)

2.7.1 抗性消声器 (7)

2.7.2 阻性消声器 (8)

2.7.3阻抗复合型消声器 (8)

2.8本章小结 (8)

第三章汽车排气消声器分析设计方法 (9)

3.1 排气噪声的频率特性 (9)

3.2 消声器的设计指标的确定 (10)

3.3消声器结构的确定 (10)

3.3.1 消声器的结构类型的确定 (10)

3.3.2 消声器进、出口管的直径

d的确定 (11)

1

3.3.3 消声器容积的确定 (11)

3.3.4 消声器截面形状的确定 (12)