Calculation and Analysis of Acoustic Characteristics of Straight-Through Perforated Pipe Muffler Based on Multilayer Sound Absorbing Material

Using the multi-physical field simulation software COMSOL,the acoustic characteristics of the multilayer sound absorbing material straight-through perforated pipe muffler are studied by the finite element method.The results show that the finite element calculation of the multilayer sound absorbing material straight-through the perforated pipe muffler agrees well with the experimental measurement results.The reliability of the finite element method for studying the acoustic performance of the straight-through perforated pipe muffler with multilayer sound absorbing materials is shown.Furthermore,the influence of some structural parameters of porous sound absorbing material and micro-perforated plate on the acoustic performance of the multilayer sound absorbing material straight-through perforated pipe muffler is analyzed.The muffler based on multilayer sound absorbing material is different from the traditional muffler.After applying the multilayer sound absorbing material to the straight-through perforated pipe muffler,the transmission loss value greatly increases,which provides new ideas and directions for future research on the muffler.

COMPUTATIONAL FLUID DYNAMICS RESEARCH ON PRESSURE LOSS OF CROSS-FLOW PERFORATED MUFFLER

The pressure loss of cross-flow perforated of physical modeling, simulation and data processing. muffler has been computed with the procedure Three-dimensional computational fluid dynamics （CFD） has been used to investigate the relations of porosities, flow velocity and diameter of the holes with the pressure loss. Accordingly, some preliminary results have been obtained that pressure loss increases with porosity descent as nearly a hyperbolic trend, rising flow velocity of the input makes the pressure loss increasing with parabola trend, diameter of holes affects little about pressure loss of the muffler. Otherwise, the holes on the perforated pipes make the air flow gently and meanly, which decreases the air impact to the wall and pipes in the muffler. A practical perforated muffler is used to illustrate the available of this method for pressure loss computation, and the comparison shows that the computation results with the method of CFD has reference value for muffler design.

PREDICTION OF ACOUSTIC PERFORMANCE IN EXPANSION CHAMBER MUFFLERS WITH MEAN FLOW BY FINITE ELEMENT METHOD

The equation of wave propagation in a circular chamber with mean flow is obtained. Computational solution based on finite element method is employed to determine the transmission loss of expansive chamber. The effect of the mean flow and geometry (length of expansion chamber and expansion ratio)on acoustic attenuation performance is discussed, the predicted values of transmission loss of expansion chamber without and with mean flow are compared with those reported in the literature and they agree well. The accuracy of the prediction of transmission loss implies that finite element approximations are applicable to a lot of practical applications.

Theoretical Calculation and Analysis of Muffler Based on Multilayer Sound Absorbing Material

The multilayer impedance composite sound absorption structure of the new muffler is proposed by combining the microporous plate structure with the resonant sound absorption structure of the porous material.Firstly,the acoustic impedance and acoustic absorption coefficient of the new muffler structure are calculated by acoustic electric analogy method,and then the noise attenuation is calculated.When the new muffler structure parameters change,the relationship among the noise frequency,the sound absorption coefficient and the noise attenuation is calculated by using MATLAB.Finally,the calculated results are compared with the experimental data to verify the correctness of the theoretical calculation.The variation of resonance peak,resonance frequency and attenuation band width of each structural parameter is analyzed by the relation curve.The conclusion shows that it is feasible to use multilayer sound absorbing materials as the body structure of the new muffler.And the influence relationship between the change of various parameters of the sound absorption structure with the sound absorption coefficient and noise attenuation is obtained.

A novel multi-cavity Helmholtz muffler

A novel multi-cavity Helmholtz muffler is proposed. The multi-cavity Helmholtz muffler is composed of steel structures and silicone membranes. With suitable construction, the Helmholtz muffler can be designed to exhibit negative mass density in low frequency, and the muffling frequency can be adjusted when we change the internal structure of the cavity,which will be very attractive for noise control. In this paper, we investigate the influence of the membranes and the cavities on noise reduction characteristics with theoretical calculations and simulations. The results show that the numbers of membranes and the volumes of the cavities can have a great effect on the position of the muffling frequency. The number of cavities can have a great effect on the width of the muffling frequency(reduce the noise by 10 dB). With different combinations of the membranes and cavities, we can get different muffling frequencies, which can meet different muffling demands in practical applications and is more flexible than the traditional Helmholtz cavity.

Research on Measurement Method of Muffler Performance under High Temperature and High-Speed Airflow Conditions

Ignoring the influence of flow velocity and flow temperature on muffling performance,performance tests were conducted without airflow in the development phase of the muffler which accounts to the difficulty of obtaining a perfect match between the actual noise reduction effect and the design goal.Based on the two-load test theory,a set of high-temperature and high-speed airflow simulation measurement devices for the muffler has been built.In order to avoid the impact of high-temperature and high-speed airflow on the sensor,a high temperature resistant sensor holder has been designed for the test rig.The sound pressure has been measured in the pipe by using the lead-out measurement.In addition,a variable impedance load is placed at the end of the test tube to realize the switch between two different impedance loads by the wave handle of the variable impedance load.A sound source correction method is proposed to decrease the random fluctuation of the spectral characteristics of the output noise signal,which is caused by the acoustic impedance variation at the connection between the transition pipeline and the combined sound source system.Finally,an acoustic software has been used to calculate the transmission loss of the muffler in the presence of high temperature airflow.In comparing the experimental measurements and the simulation results,the small difference shows that:the bench not only can effectively simulate high-temperature and flow velocity environment of the engine but also accurately test the transmission loss of the muffler.

Reducing the Gas Pressure Drop in Suction Mufflers of Hermetic Reciprocating Compressors

The suction muffler of hermetic reciprocating compressors is installed in order to attenuate the noise generated by the gas pulsation of the flow through the suction valve. However, the installation of the suction muffler affects the operation of the compressor owing to gas pressure drop, which causes volumetric and energetic efficiency loss due to the gas specific volume augmentation. Therefore, there is a compromise between sound attenuation and pressure drop increase, which has to be taken into account by compressor designers. In this work, it presents a numerical solution to the flow through a suction muffler in order to analyze the pressure field and point out the main contributions to the overall pressure drop of the flow. A commercial CFD （computational fluid dynamics） code was used to perform the numerical simulations and the results were validated by using experimental data. After analyzing the pressure field, the geometry of the muffler was modified intending to decrease the flow pressure drop. The geometric modification produced a 28% reduction on the overall pressure drop, without influencing the sound attenuation.

带消声功能的潜艇换热器声学性能仿真

针对潜艇消声问题,提出一种带消声功能的换热器,开展环状橡胶气囊结构消声性能研究。建立仿真模型和进行传递损失计算,证明有囊式消声器的消声效果。利用控制变量法定量改变设计参数,分别研究气腔长度、穿孔直径和穿孔率对气囊消声效果的影响规律,为潜艇换热器的流动噪声控制提供有力支撑。

基于低频吸声超构材料的复合消声器

针对管道内低频噪声难以抑制的问题,基于亥姆霍兹共振腔阵列吸声板和穿孔管消声器组合,设计了一种复合式宽带消声器。首先利用有限元法仿真分析传统穿孔管消声器,发现中低频消声能力较差,通过嵌入亥姆霍兹共振腔阵列吸声板吸收中低频噪声。采用仿真与实验的方式研究吸声板的声学性能:在400∼1000 Hz频段内的平均吸声系数达到了0.88。然后对复合式消声器进行数值模拟及3D打印阻抗管实验测试对比:复合式消声器在400∼1718 Hz频率范围内的平均传递损失为18.15 dB。最终实现了管道内全频带噪声有效控制。

基于近似模型的弹性背腔穿孔管消声器声学性能优化

弹性背腔穿孔管消声器利用声波和弹性管壁的耦合作用,相比于穿孔管消声器具有更好的低频消声性能。为了进一步提高该消声器的低频、宽频消声能力,采用遗传算法对其进行优化。首先,利用COMSOL有限元软件建立该消声器的传递损失计算模型。其次,分析弹性管壁材料对消声器低频消声性能的影响,并选取橡胶复合材料作为弹性管壁材料。再次,由于所采用的有限元模型计算耗时长,为节约时间资源,利用径向基函数(Radial Basis Function,RBF)神经网络方法建立近似模型代替有限元计算模型。最后,利用近似模型结合遗传算法进行全局寻优,获得该消声器结构参数的优化结果,并利用有限元模型验证优化的准确性。结果表明:优化后在100~1000 Hz低频段范围内弹性背腔穿孔管消声器消声带宽增加62%,且平均传递损失提高3.6 dB。

基于GT-Power的排气轰鸣噪声控制与优化研究

针对某1.5T三缸发动机车型排气尾管噪声在1 280 r/min、1 550 r/min转速下出现轰鸣声的问题,对其排气系统消声器结构进行优化设计,从而达到消除该轰鸣声的目标。分析了排气尾管轰鸣声的产生原因,并解释了轰鸣产生的机理,得出该轰鸣声是消声器在96~116 Hz下消声量不足的结论。通过GT-Power软件基于传递损失仿真结果优化了排气系统消声器结构,并建立发动机模型,与优化后的排气系统模型进行噪声仿真,仿真结果满足优化要求。在整车半消声室中进行了排气尾管噪声测试试验,测试结果验证了分析结果的准确性,且优化方案排气尾管轰鸣声消失,中高转速下噪声降低2 dB(A)

双层动车复合式冷却系统散热与噪声控制的优化研究

高速双层动车由于其内部空间紧凑以及元件的高功率化,冷却系统存在整体散热性能较差、噪声污染严重的问题。为此,通过冷却系统空气流场的数值模拟与试验研究,对其散热性能和噪声控制进行了优化。参照常用的冷却系统空气流道结构,基于双层动车复合式冷却系统的技术参数要求,对其尺寸进行了初步设计计算。分别采用多孔介质模型和多参考系(MRF)对复合式冷却系统换热器的芯体结构与旋风过滤器进行简化,并对其空气侧流场进行数值模拟。研究结果表明:风机入口处存在局部涡流,导致流体进入通风机的角度混乱,影响风机有效做功,在工作环境下系统风量(2.96 m^(3)/s)远小于设计值(3.35 m^(3)/s);同时局部涡流产生较大的气动噪声。此外,换热器入口的风速分布不均匀,导致系统冷却能力不足。针对上述问题,对空气流道结构进行了优化。调整了进、出口消声器的3个流道的流通面积,并在过渡段设置“喇叭型”导流结构来改善换热器进口处风速的均匀性;在冷却系统进、出口增加弧线型消声器能进一步降低噪声。结果表明:空气流道结构优化后水侧散热功率从33.18 kW增加到41.55 kW,油侧散热功率从157.82 kW增加到173.82 kW,系统加权平均噪声值从74.95 dB(A)降低到72.21 dB(A)。本研究可为类似工程项目冷却系统的优化设计提供参考,有助于改善乘坐体验和车辆运行的经济性。

任意边界条件下弹性背腔膜式消声器声学特性分析

弹性背腔膜式消声器由弹性背腔以及弹性内膜组成,通过声场与弹性内膜及弹性外膜的耦合作用,降低消声器下游的透射声能,在低频具有较好的宽带消声效果。为求解任意边界条件下的弹性背腔膜式消声器的传递损失,基于能量原理,建立了弹性背腔膜式消声器的声振耦合模型。采用边界弹簧约束来实现弹性膜的任意边界条件,进而分析边界约束对传递损失特性的影响。结果表明,理论计算结果与有限元结果吻合良好;结构边界约束对系统声学特性影响显著,增强外膜边界约束,能获得低频宽带消声效果;减弱内膜边界约束,能使最低消声频率向低频移动。

双螺杆空压机消声器设计与性能分析

针对双螺杆空压机在工作过程中壳体产生较大噪声的问题,利用有限元分析技术,对空压机壳体进行噪声频谱研究,得到在100~1500 Hz时,双螺杆空压机壳体噪声频谱图。采用添加消声器的方法进行降噪处理,并对消声器进行了结构优化设计,消除了谐振现象;将所设计的消声器安装在双螺杆空压机吸气口处,对比发现该消声器具有较好的降噪效果。研究成果可对双螺杆空压机降噪起到一定的参考作用。

燃料电池用离心式空压机抗性消声器设计及其消声效果分析

基于计算流体力学耦合计算气动声学的方法,在不同空压机运行工况下分析了穿孔消声器的降噪效果,量化了消声器内的热声转化关系。结果表明,穿孔消声器的空腔厚度和穿孔率对高频组分声波的吸消声起着决定性作用。与低频声波相比,穿孔消声器对高频组分声波的消声效果更好;随转速的增加,穿孔消声器对高频组分声波的消声效果逐渐增强,而对低频组分声波的消声效果几乎无变化。对穿孔消声器内的热声转化分析表明,低转速运行工况下,消声器消声前后声振荡能量几乎全部转化为工质可用能,而在中高转速运行工况下,声振荡衰减的能量转化为工质可用能的比例较小。为设计出可以在宽运行工况下实现宽频降噪的消声器,高转速运行工况下低频组分声波的消声应该作为重点优化的目标,同时也要考虑低转速运行工况下消声器消声前后的热力学性能的改善。为降低离心式空压机的气动噪声提供了一种新的方法,为设计宽工况适应性的高效空压机消声器提供了理论基础。

船用空调阻性消声器消声量计算方法优化的实验研究

在船用空调系统中,由于已有的阻性消声器消声量的经验公式忽视了高频失效效应的影响,使得原有的消声量计算方法在高频段不再适用,为了探究出一个符合船用空调阻性消声器消声量的计算公式,通过分析实验数据,选择一个与模型相适应的经验公式,最终在此基础上结合实际工况对经验公式进行修正与检验。结果表明:当频率处于中低频时,罗杰斯公式的消声量计算值与插入损失值的变化趋势十分接近,误差在4dB左右,但在高频段,由于高频失效效应,经验公式不再适用;其次拟合出来的经验公式修正式,在倍频程下的消声量值与实际工况相互一致,误差低于3dB,满足实验预期要求。

管道流体流动对水液压消声器消声性能影响研究

流体噪声通过水管路辐射到海洋中,严重影响水下航行器的隐蔽性及安全性,加装水管路消声器是减小水管路辐射噪声的重要措施。考虑到流体流动对水管路消声器性能的影响,利用膨胀式消声器内部流场数值计算结果,采用平均流速理论,计算考虑内部流体流动时的消声器的传递损失,探究流速结构对消声器传递损失的影响。计算结果表明,在低流速条件下,流速对消声器的传递损失影响不大,但流体再生噪音会在特定频率下使消声器传递损失出现低值,需要对消声器结构进行改进。计算结果表明,通过修正消声器结构参数以及串联共振腔室消声器结构可有效提升特定频率下的消声器低值。可为降噪计算方法提供理论参考。

一种应用于汽车进气系统的新型消音器设计

近年来,随着我国汽车保有量的急剧上升,汽车噪声已经成为城市噪声污染的主要来源之一,直接影响居民的身心健康,汽车噪声污染问题亟待解决。汽车噪声源中,进气噪声因气体流体动力学特性极其复杂,因而没有固定的降噪措施。针对这个难题,设计了一种集空气滤清器和消音器一体的错列复合阻抗式消音器,可以同时实现除尘和降噪两种功能,而且不会在周期性进气脉冲噪声的激励下产生额外的共振噪声。

重庆地铁各型声屏障综合降噪效果研究

通过在重庆地铁各型声屏障的实际设置区段,对距外轨中心线7.5 m处的近轨声场和敏感建筑处进行同步噪声测试,分析数据并建立符合实际的重庆地铁声屏障降噪效果预测模型,并通过实测和模拟的方法研究重庆地铁各型声屏障的综合降噪效果。结果表明:对敏感建筑整体降噪效果最好的为顶部设置消声百叶的全封闭声屏障,敏感建筑处的噪声为56.4~61.1 dB(A),整体降噪效果最差的为2.5 m直立式声屏障,敏感建筑处的噪声为67.8~73.2 dB(A);使用单一线声源模式模拟全封闭声屏障降噪结果与实测误差较大,需在模型中通过添加结构噪声源等方式进行修正;利用修正后的预测模型,预测得出的降噪效果与实测结果具有较好的吻合性,各型声屏障中对近轨声场以及敏感建筑处降噪效果均最好的为顶部设置消声百叶的全封闭声屏障,实测降噪效果为4.9~15.9 dB(A),模拟得出降噪效果为7.7~17.1 dB(A)。

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。