汽车排气系统流动特性与声学特性研究

发布时间：2018-03-03 05:13

本文选题：排气系统　切入点：消声器　出处：《重庆交通大学》2016年硕士论文　论文类型：学位论文

【摘要】：研究发动机排气系统性能是排放控制和噪声控制的要求。采用传统方法对发动机排气系统的流动特性和声学特性进行研究,难以获得与实际相符的计算结果。采用有限体积法、声学有限元法等三维数值模拟方法研究发动机排气系统性能,既能模拟气体的实际流动情况,又能考虑诸多因素对排气系统性能的影响。本文以某企业某款发动机排气系统为原模型,对其流动特性、声学特性以及流动特性对声学特性的影响进行了分析研究。首先,采用流固耦合方法对排气系统的流动特性进行研究。对排气系统的流固耦合模型进行三维数值模拟计算,得到了发动机全速全负荷工况下排气系统内的压力场、温度场以及速度场分布情况。根据流场分布结果,进一步分析了排气系统压力损失的原因,提出了温度场分析研究的必要性,给出了系统内部流体的具体流动状况。其次,采用某企业搭建的试验台架,以排气系统上6个测试点的排气背压值和排气温度值作为比较对象,验证了三维流固耦合数值模拟计算结果的可靠性。其后,采用声学有限元法对排气系统的声学特性进行研究。对消声系统的声学有限元模型进行声学有限元分析,以传递损失作为评价指标,分别对前消声器、后消声器、整个消声系统的声学特性进行分析,得到了前、后消声器以及整个消声系统的传递损失曲线,并给出了部分频率值下的声压分布云图。最后,对温度、流速这两个因素对消声器声学特性的影响进行研究,得到了耦合温度、流速因素的消声系统传递损失曲线。研究结果表明:考虑温度因素后,消声频谱向高频移动,表现为传递损失曲线的第一个峰值由320Hz移向480Hz,第二个峰值由400Hz移动到670Hz。低频段的平均消声量降低了约20dB,消声效果变差,中高频段的平均消声量增加了15dB左右,消声特性得到了一定的改善;考虑流速因素后,平均消声量相较与未考虑流速因素时略有增加,增幅约为3dB。总体来看,温度对声学特性的影响比流速对声学特性的影响更为明显。
[Abstract]:To study the performance of engine exhaust system is the requirement of emission control and noise control. The flow and acoustic characteristics of engine exhaust system are studied by traditional method. Three dimensional numerical simulation methods such as acoustic finite element method (FEM) are used to study the performance of engine exhaust system, which can simulate the actual flow of gas. The influence of many factors on the performance of the exhaust system can be considered. In this paper, the flow characteristics, acoustic characteristics and the effects of the flow characteristics on the acoustic characteristics of a certain engine exhaust system in an enterprise are analyzed and studied. The fluid-solid coupling method is used to study the flow characteristics of the exhaust system. The three-dimensional numerical simulation of the fluid-solid coupling model of the exhaust system is carried out, and the pressure field in the exhaust system at full speed and full load is obtained. Temperature field and velocity field distribution. According to the result of flow field distribution, the cause of pressure loss in exhaust system is further analyzed, the necessity of temperature field analysis is put forward, and the specific flow status of fluid in the system is given. In this paper, a test rig built by an enterprise is used to compare the exhaust back pressure and exhaust temperature of six test points on the exhaust system. The reliability of the numerical simulation results of three-dimensional fluid-solid coupling is verified. Acoustic finite element method is used to study the acoustic characteristics of the exhaust system. The acoustic finite element analysis of the acoustic finite element model of the silencing system is carried out. The acoustic characteristics of the whole silencing system are analyzed, the transmission loss curves of the front and rear mufflers and the whole silencing system are obtained, and the sound pressure distribution clouds under some frequency values are given. Finally, for the temperature, The influence of two factors on the acoustic characteristics of muffler is studied, and the transmission loss curves of the coupling temperature and velocity factor are obtained. The results show that the frequency spectrum of the muffler moves to the high frequency after the temperature factor is taken into account. The first peak value of the transmission loss curve moved from 320Hz to 480 Hz, and the second peak value moved from 400 Hz to 670 Hz. The characteristics of noise suppression have been improved to a certain extent, and the average silencing rate is slightly higher than that when the velocity factor is taken into account, and the increase is about 3 dB, as compared with that when the velocity factor is not taken into account. The effect of temperature on acoustic characteristics is more obvious than that of velocity.
【学位授予单位】：重庆交通大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：U464.134.4

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