穿孔管消声器消声性能的有限元计算及分析

使用有限元法计算穿孔管消声器的传递损失,并与实验测量结果进行了比较,二者吻合良好。穿孔率 相同而孔径不同的两个穿孔管消声器的传递损失与具有相同直径和长度的简单膨胀腔消声器的传递损失比较表 明,穿孔管对消声器的低频性能影响较小,而对中频消声性能影响很大、对高频消声性能影响有限。     

排气消声器传递损失的实验测量与分析

介绍消声器传递损失的测量方法,包括声波分解法、两负载法、两声源法和脉冲法。在消声器声学性能试验台上采用两负载法测量无流和有流时简单膨胀腔和直通穿孔管消声器的传递损失。测量结果表明：穿孔率对穿孔管消声器低频消声性能影响较小,对中高频消声性能影响较大,增加穿孔率能够拓宽穿孔管消声器的有效消声频率范围;气流对直通穿孔管消声器的声学性能有一定影响,穿孔率越低影响越大,随着流速的增加,低频段传递损失变化不大,高频段的传递损失显著增加。     

多腔穿孔管消声器传递损失参数灵敏度分析

传递损失作为穿孔管消声器声学性能的评价指标,可以采用有限元法计算。文章提出数值联合仿真方法计算其传递损失,并与试验结果进行对比验证。进而采用该方法结合正交实验法研究多腔穿孔管消声器传递损失参数灵敏度。研究结果表明,数值联合仿真方法可以准确计算穿孔管消声器传递损失,比传统方法节省2/3的时间。在中频段,进出口管半径、扩张腔半径和第一腔结构参数对多腔穿孔管消声器传递损失影响明显。     

《扩张室式消声器声学特性的有限元分析》

应用有限元法分析进出口管同轴扩张室式消声器的声学性能,计算其传递损失并与一维平面波理论计算对比,分析一维平面波理论的适用范围。通过分析出口管偏置消声器,双出口管消声器和两腔消声器的声学性能表明：出口管位置和数量影响消声器中高频消声性能,而两腔消声器则能明显改善消声器中低频的消声效果。     

三角截面内管的阻抗复合消声器声学特性研究

以三角截面内管阻抗复合型消声器为研究对象,推导其消声量数学表达式,基于GT-POWER软件建立消声器传递损失和阻力损失计算仿真模型,分析消声器结构、材料参数与消声性能的关系,得到孔径、穿孔率、变径管倾角、吸声材料及容重对消声器传递损失及背压的影响规律,并通过实验验证仿真结果的正确性。研究结果可为具有三角截面消声器的设计和优化提供参考。     

双层分流对冲穿孔管结构消声特性研究

发动机排气系统中的噪声特性为高频、宽频带，以及排气气流作用下产生的再生噪声，传统的消声结构不能有效地解决该噪声问题。因此，提出通过将锥形分流单元与双层穿孔管相结合的消声方法。首先通过一个锥形分流单元对进入消声器的气流进行分流，分流后的气流在第一层穿孔管外腔得到充分的减速，再经过第一层穿孔管进行初次消声，然后通过第二层穿孔管进行二次消声，最后通过第二层穿孔管上的小孔进入到对冲腔，使气流在对冲腔发生对冲，气流在对冲的过程中速度逐渐降低，再生噪声减小消声效果增强。通过对双层穿孔管结构的传递损失进行推导，分析结构参数对消声性能的影响，得到传递损失的影响因素与变化特性，并进行实验验证。实验结果表明：提出的消声方法能够在高频入射声波的情况下维持较高的传递损失和较宽的消声频带。     

内部结构对充水膨胀腔消声器声学性能的影响

结构声耦合效应对充水消声器的声学性能具有重要的影响,利用频域有限元法,结合二维轴对称结构声耦合数值模型分析消声器内部声场,研究消声器内部插入管和环形挡板对膨胀腔水消声器声学特性的影响。数值研究表明：结构声耦合效应会使传递损失的通过频率和峰值频率向低频移动,并压缩消声频段;插入管的结构声耦合效应导致传递损失曲线出现明显峰值,这与插入管的固有模态有关,增加插入管长度时,其一阶固有频率降低,峰值消声频率向低频移动,这有利于低频噪声的衰减;对比双级膨胀腔消声器,挡板会提高低频消声量,挡板厚度会对低频消声量产生明显的影响,但挡板的位置对低频消声量影响不大。     

穿孔管阻性消声器声学特性的有限元分析

将有限元法应用于预测穿孔管阻性消声器的声学性能。直通穿孔管阻性消声器传递损失的有限元计算结果与实验测量结果吻合良好,表明了有限元法预测穿孔管阻性消声器声学性能的适用性和精度。进而有限元法被用于研究吸声材料的填充密度(流阻率)、吸声材料的厚度和穿孔率对穿孔管阻性消声器声学性能的影响,结果表明,增加吸声材料的填充密度,可以改善中高频消声性能,并使峰值频率向低频方向移动;增加吸声材料厚度,可以改善阻性消声器的中高频消声性能,而对低频声学性能影响较小;膨胀腔包覆吸声材料可以改善中高频消声效果,同时消除通过频率;增加穿孔率,可以提高穿孔管阻性消声器的高频消声性能,并使共振峰向高频方向偏移;吸声材料背后增加空气腔,可以在较宽的频率范围内获得较为平坦的消声曲线。     

非均匀流条件下穿孔管消声器传递损失计算方法与特性分析

实际应用中的消声器通常具有比较复杂的内部结构，其内部流体速度分布不均匀，而且消声器内部的回流管路和穿孔元件使得消声器内部的流体流动更加复杂，其消声性能不可避免地受到流体流动的影响。为了计算非均匀流条件下穿孔管消声器的传递损失，应用计算流体力学(Computational Fluid Dynamics, CFD)软件FLUENT计算消声器内部的流场，然后将流体属性通过网格映射的方式转移到LMS Virtual Lab声学有限元模型中，并且选用不同的穿孔阻抗模型计算消声器的传递损失，计算结果与实验测量结果进行了比较。文章对消声器内部流场的流动特征也做了仔细地分析，并研究了气体流速对消声器传递损失的影响，随着气体流速的增加，消声器的传递损失会增大，共振峰的峰值会减小。     

部分穿孔管消声器声学性能有限元分析

穿孔管消声器因具有良好的声学性能和较低的压力损失而被运用于消除内燃机排气噪声。通过运用有限元法研究部分穿孔消声器穿孔率、插入长度、周向和轴向穿孔分布、扩张腔直径等设计参数对消声器消声性能的影响。得到如下结论:穿孔率增大、插入长度变短会引起低频共振峰向高频方向偏移;穿孔率增大、扩张腔直径减小都会引起有效消声频率范围的拓宽;穿孔的轴向、周向分布对消声器消声性能没有影响。     

Boundary element acoustic analysis of hybrid expansion chamber silencers with perforated facing

The substructure boundary element approach is developed to predict and analyze the acoustic attenuation characteristics of hybrid expansion chamber silencers with perforated facing. The silencers are divided into a number of acoustic domains with single medium (air or sound-absorbing material), and treating the sound-absorbing material as an equivalent fluid with complex-valued density and speed of sound (or complex-valued characteristic impedance and wavenumber), and then the boundary element method (BEM) may be applied to each domain leading to a system of equations in terms of acoustic pressure and particle velocity. Using the specific acoustic impedance of perforate, which takes into account the effect of sound-absorbing material, the relationship of acoustic pressures and particle velocities between the inlet and outlet of silencer may be obtained and then transmission loss is determined. For the straight-through perforated tube reactive and dissipative silencers, the predictions of transmission loss agree reasonably well with experimental measurements available in the literature, which demonstrated the applicability and accuracy of the present approach. The BEM is then used to investigate the effect of internal structure on the acoustic attenuation characteristics of hybrid expansion chamber silencers with perforated facing. The numerical results demonstrated that the hybrid expansion chambers may provide higher acoustic attenuation than the reactive expansion chamber in the mid to high frequency range.     

穿孔管阻性消声器消声性能计算及分析

一维解析法和三维子结构边界元法被用于计算和分析穿孔管阻性消声器的消声性能，以及考查消声器内非平面波对消声特性的影响。直通穿孔管阻性消声器传递损失的预测结果与实验测量结果比较表明：一维解析法只适合于消声器的低频声学性能计算，对于高频声学性能的精确预测需使用三维计算方法。边界元法进而被用于研究吸声材料的填充密度（流阻率）和几何参数对穿孔管阻性消声器消声性能的影响。增加吸声材料的填充密度、穿孔管的穿孔率和穿孔长度、以及吸声材料的厚度，均能有效地改善阻性消声器的中高频声学性能，而对消声器的低频消声效果影响较小。     

《有流船用排气消声器声学性能分析》

用发展的双倒易边界元法考察了气流对双级膨胀腔消声器消声性能的影响，结果表明较高马赫数亚音速流的影响不可忽略。同时总结了内插管数量，进口位置和导流环结构对消声器传递损失的影响规律，具有一定的实用价值。     

柴油机SCR催化转化消声器的消声性能

采用声学有限元法对抗性消声器进行模拟,分别研究侧置进气插入管和穿孔管消声器的消声性能。以侧置进气插入管为基础,对末端腔体不同布置形式进行研究。然后将SCR催化剂载体耦合到消声器中,计算出SCR催化转换消声器的传递损失。结果表明,该催化转换器具有较好的消声效果。     

A study on the transmission loss of straight‐through type reactive mufflers

Abstract

The following study presents a newly developed approach for modeling perforated muffler components, such as partially perforated extended inlet/outlet elements. After evaluating the transfer matrices of all sub‐elements, the transfer matrices product is obtained by multiplication of partially perforated extended inlet/outlet elements. For acoustic impedance in the linear regime, a closed form solution of the partially perforated intruding tube muffler transmission loss was first obtained. In the case of zero mean flow, the predicted results for the various muffler configurations strongly corresponds to the measured values within the limitations of the one‐dimensional theory. By tuning the lengths and associated physical parameters to the in‐situ case of various tubular elements, one can achieve rapid and economical modeling of frequently used commercial reactive mufflers as well as mufflers for other industrial applications can be achieved. This aeroacoustic modeling ability is very useful for vehicular muffler designer especiallly during the preliminary design stages.     

Fast multipole boundary element approaches for acoustic attenuation prediction of reactive silencers

The fast multipole boundary element method (FMBEM) is applied to predict the acoustic attenuation performance of reactive silencers. In order to overcome the difficulty of singular boundaries for the acoustic computation of reactive silencers with internal thin wall structure or/and perforated components, two approaches, the substructure FMBEM (Sub-FMBEM) and mixed-body FMBEM (MB-FMBEM) are proposed, and the theoretical foundations and numerical processes of the both approaches are introduced. The studies demonstrated that the ordering of column vectors and numbering of nodes in the Sub-FMBEM have great influence on the convergence of iteration, and the MB-FMBEM may reduce the number of elements and the computational complexity since it only needs to discretize one side boundary of the thin wall and perforated components and it is not necessary to create the interfaces. The Sub-FMBEM, MB-FMBEM and Sub-BEM are then employed to calculate the transmission loss of reactive silencers with thin wall components and perforated tubes, the computational accuracy and efficiency of the approaches are validated. The data of precomputing time and total iterative computational time demonstrated that, the computational efficiency of Sub-FMBEM will descend as the frequency arising, and the Sub-FMBEM may reveal higher computational efficiency than Sub-BEM only when the number of nodes is big enough.