【作者】 张宏宇；

【导师】 包钢；

【作者基本信息】 哈尔滨工业大学 ， 机械电子工程， 2013， 硕士

【摘要】 气动系统在工作时往往产生很大的排气噪声，为降低工作环境噪声，通常要在系统的排气端加装消声器。常用的封闭腔气动系统消声器在某些应用场合容易引入过大的压降，影响上游系统的工作性能，而且长期使用时，容易导致异物堆积阻塞气流通路。因此本文对气动用通孔式消声器展开研究以期解决上述应用领域面临的困难。本文通过改进的Johnson-Allard等效流体模型计算通孔式消声器内多孔吸声材料的等效特征参数随声波频率的变化规律。通过经验公式计算出穿孔板特征阻抗随声波频率的变化规律。结合多孔吸声材料及穿孔板模型，建立通孔式消声器的二维解析模型，讨论特征波数方程的求解，采用模态匹配法计算消声器传递损失。比较保留不同模态阶次对传递损失计算的影响，说明为得到精确的通孔式消声器传递损失预测结果，进出口管道内保留两阶声波模态即可，而消声腔内应至少保留三阶声波模态。通过声学有限元法分析讨论了吸声材料的流阻率、孔隙率、形状因子、粘性及热特征长度等几个参数对消声器传递损失的影响，结果表明，流阻率尽量取大，形状因子和两种特征长度尽量取小，有助于提高消声器传递损失，孔隙率对传递损失的影响不大。还讨论了穿孔板的穿孔率、孔径及厚度对消声器的影响，结果表明，对于通孔式消声器来说，穿孔板的引入总体上看对低频段传递损失增加有限，但对有效消声频段的缩小明显，随着穿孔率的降低及孔径增大，这种不利的影响更加明显，穿孔板厚影响不是很大。当选择穿孔板作为护面结构时，应尽量选择孔隙率大孔径小的穿孔板，避免其影响多孔吸声材料发挥作用。讨论了消声器消声腔长度及吸声材料厚度对于消声器传递损失的影响，结果表明消声器消声腔长度越长，吸声材料厚度越大，消声器的各频段传递损失也越大。通过声学有限元计算讨论了插入管、锥形流道、气隙、消声腔内隔板等消声器改进结构对传递损失的影响。结果表明增加合理的插入管、截面尺寸由小变大的锥形流道、消声腔内隔板有助于提高消声器传递损失，尤其是能改善消声器在通过频率附近的降噪能力。而气隙结构不利于消声器传递损失的提高，截面尺寸由大变小的锥形流道对消声器传递损失提高作用不明显。通过进一步的理论分析，指出插入管及消声腔内隔板对消声器消声能力的改进作用，主要是通过影响通过频率下声波特征模态的激发与传播实现的，并指出改进结构的最佳布置位置位于消声腔模态节点附近。通过声级计测量通孔式消声器试样安装于真空发生器尾部时，消声器试样出口正前方1m总声压级随真空流量变化，总声压级随真空发生器入口压力变化。通过传声器采样及频谱分析，得到各消声器试样噪声频谱曲线。实验表明在被试材料中，棉及岩棉的吸声表现是最好的。实验验证了填充材料流阻率越大、消声腔长度越长、消声腔材料越厚，消声表现越好的结论。对于几种改进结构的实验比较表明，截面尺寸由小变大的锥形流道、消声腔内隔板有助于提高消声器消声能力。但是入口插入管没能提高消声器消声效果，而理论预测中表现平平的截面尺寸由大变小的锥形流道却提高了消声器消声能力。更多还原

【Abstract】 Pneumatic systems usually produce large exhaust noise in typicalapplications. In order to control the noise pollution to the working environment,it is necessary to attach silencers to all the exhaust pipes in these systems.However, the widely-used close-chamber pneumatic silencers may result inexcessive pressure drop which will influence the working performance of theupstream systems and accumulation of filth with long time usage which willblock the air pass in some specific applications. Hence, research on thepneumatic through-hole silencer is conducted in order to overcome theshortcomings of these applications.The relationship of characteristic parameters of porous absorbing material inthe through-hole silencers with sound frequency is calculated with Johnson-Allard equivalent fluid model. The relationship of characteristic impedance ofperforated plate with sound frequency is calculated with empirical equations.Combined with these results, two dimensional analytical model of the through-hole silencer is established. The solution techniques of the characteristic wavenumber equations are discussed and the transmission loss (TL) is calculated bythe mode matching method. It is concluded that two acoustic modes in the inletand outlet pipe and at least three acoustic modes should be preserved in thechamber to obtain precise enough prediction of TL by comparison results of TLwith different mode orders.The influences of parameters of porous absorbing material includingporosity, resistivity, tortuosity, viscous and thermal characteristic length on theTL of the through-hole silencer are discussed by acoustic finite element analysis.Results indicate that material with larger resistivity, smaller tortuosity, viscousand thermal characteristic length tends to improve the TL while the influence ofporosity is negligible. The influence of perforated plate including the porosity ofthe plate, hole diameter and wall thickness are also discussed. Results indicatedthat the perforated plate structure obviously shorten the effective frequencydomain of the through hole silencer while only bring limited improvement to TLin the low frequency, and the influence of wall thickness is minimal. With largerperforation porosity and hole diameter, these disadvantages also become moreevident. Thus it is recommended to choose perforated plates with largerperforation porosity and smaller hole diameter as the protection of porous material. The influences of chamber length and porosity material lining thicknessare also discussed. It is concluded that hrough-hole silencer with larger chamberlength and lining thickness have better performance over the whole frequencydomain.The effects of improved silencer structures including extended tube,conical airway, air gap, and partitions inside the chamber on the TL of thethrough-hole silencer are discussed through acoustic finite element analyses.Results indicate that extended tubes with proper length, conical airway withgradually increasing cross section, partitions inside the silencer chamber couldimprove the TL of the through-hole silencer while the air gap tends to impair thesilencing performance and the conical airway with gradually decreasing crosssection show little influence. By further analyses, it is pointed out that theimprovements of the extended tubes and partitions on the through-hole silencers’TL are realized by preventing specific sound modes excitement and propagationunder characteristic frequencies and thus the optimal configurations of thesestructures are near the modal nodes of the through-hole silencer chamber.The relationship of total sound pressure level of the noise of the through-hole silencer attached to a vacuum generator with the vacuum flux and inletpressure is obtained by the sound level meter at the measurement point1m infront of the exhaust of the silencer. Noise signals are recorded by the microphoneand the frequency spectrum of the through-hole silencers are obtained by signalprocessing. Experiment results show that the most promising materials amongtest specimens are cotton and rock wool. The conclusions that material, withlarger resistivity, longer silencer chambers, thicker linings will improve thethrough-hole silencer’s performance are verified by the experiment. Experimentresults also show that the conical airway with gradually increasing cross sectionand partitions are effective in improving the performance of the through-holesilencer. However, the inlet extended tube didn’t improve the performance of thesilencer as expected while the conical airway with decreasing cross sectionwhich show medium effect in the simulation unexpectedly improve theperformance of the silencer.更多还原