亥姆霍兹共振腔不同连接方式的传递损失与特性分析

为了研究亥姆霍兹共振腔不同连接方式的共振频率和传递损失,运用Virtual.Lab Acoustics软件建立单个和两个亥姆霍兹共振腔的有限元模型。仿真计算在串联或并联情况下两个亥姆霍兹共振腔当腔体体积相同和体积不同时的传递损失,并进行吸声特性分析。研究发现,两个体积相同的亥姆霍兹共振腔并联时共振频率略微增大,吸声性能则显著提高;当两个体积不同的亥姆霍兹共振腔并联时共振频率为各自腔体共振频率,互不影响;当两个亥姆霍兹共振腔串联时,振动规律符合二自由度弹簧-质量振动系统的振动规律。把亥姆霍兹共振腔并联关系推广到穿孔板,建立穿孔板孔和背腔的有限元模型和实体模型并进行实体模型的阻抗管试验,对穿孔板仿真结果与实验结果进行对比,验证了仿真模型的正确性。     

SC6350C后桥异响噪声控制研究

针对SC6350C汽车在40km/h滑行时后桥产生的异响噪声,利用频谱分析技术分析了构成异响噪声的主要频率成分。在此基础上基于薄膜阻尼理论和亥姆霍兹共振原理,分别设计了薄膜阻尼消声结构和亥姆霍兹穿孔板吸声结构。台架实验和整车道路实验均表明,两种结构对降低后桥异响均有显著效果,车内异响噪声亦得以基本消除,且亥姆霍兹穿孔板吸声结构的效果略优于薄膜阻尼消声结构。     

亥姆霍兹脉动衰减装置设计与数值模拟

亥姆霍兹共鸣器是一种常见的声学元件,可应用于衰减管道内气流脉动。根据API618标准推荐的亥姆霍兹共鸣器设计方法,针对往复压缩机排气管路设计气流脉动衰减装置;搭建三维压缩机气流脉动数值分析模型,计算发现管路内存在频率高达120 Hz的气流压力脉动;根据亥姆霍兹共鸣器的低通滤波特性,使用截止频率为110 Hz的亥姆霍兹共鸣器可削弱频率为120 Hz的气流脉动;在三维压缩机气流脉动分析模型中添加截止频率为110 Hz的亥姆霍兹共鸣器,发现频率为120 Hz的气流压力脉动幅度被削弱了76%。     

汽车天窗风振噪声的道路试验研究

在理论层面上介绍汽车天窗开启时产生低频风振噪声的原理,总结汽车行业研究天窗风振噪声的研究方法,即倾向于前期仿真,而对实车阶段的风振噪声缺少验证。针对某款车型进行道路上风振噪声测试,结合主观感受,研究汽车天窗开启时产生风振噪声的客观水平。利用该分析技术在节约风洞试验成本基础上为产品的改进提供客观评判标准,并结合仿真分析为前期开发提供策略。     

基于CFD仿真的SUV侧窗风振特性

当前天窗风振已得到控制,而侧窗风振难以控制,且侧窗风振特性相关研究较少.以某SUV为例,结合风洞试验与仿真,探究风振噪声仿真精度的影响因素,通过仿真研究侧窗风振噪声分布与风振特性.结果表明,湍流模型采用大涡模拟(Large eddy simulation,LES)与改进的延迟分离涡模拟(Improved delayed detached eddy simulation,IDDES)精度较高,而可实现K-ε的精度较差;介质采用可压气体的仿真精度更高,采用不可压气体时风振声压级远低于实际;侧窗风振在车内均匀分布,前窗风振弱于后窗;随风速升高,侧窗风振声压级先高后低,频率递增;侧窗风振声压级不随车窗开度而连续变化;负角度偏航时,左侧窗风振增强,反之风振减弱;随乘员人数增加,风振先减弱后增强;任意组合开窗可以抑制侧窗风振,右前窗开启时左后窗风振最低.对风振仿真精度影响因素的研究与侧窗风振特性的总结,可为乘用车侧窗风振的仿真开发与控制提供参考.     

正方形亥姆霍兹线圈的磁场均匀性

利用三个正方形亥姆霍兹线圈构建三维匀强磁场,并分析其匀强磁场区域特性。将正方形亥姆霍兹线圈视为四段载流导线,采取分段计算然后矢量叠加的方法,分析正方形亥姆霍兹线圈轴线上和空间磁场强度及其均匀性,及其仿真数据结果。最后得到正方形亥姆霍兹线圈三维匀强磁场的结构模型及相关数据分析,证明了三维亥姆霍兹线圈产生的磁场满足匀强磁场要求。     

共振型液压消声器的研究

本文讨论亥姆霍兹式和多孔同心式共振型液压消声器的设计准则,及其在液压系统中最佳安装位置的确定方法,以及系统工作参数对液压消声器衰减特性的影响。     

亥姆赫兹共鸣器衰减压缩机气流脉动的数值模拟与实验研究

提出在往复压缩机阀腔处安装亥姆赫兹共鸣器,来消减阀腔及管路中气流脉动的措施,并应用平面波动理论及转移矩阵方法,数值模拟了亥姆赫兹共鸣器的衰减特性,对安装亥姆赫兹共鸣器前后的脉动进行了比较。设计了实验装置,在实验室两级压缩的橇装往复压缩机一级排气管路上对数值模拟结果进行了验证。研究结果表明:亥姆赫兹共鸣器能够有效衰减阀腔及管路内的脉动压力,可将阀腔内的脉动压力衰减40.1%,且下游管路内脉动压力也可得到有效衰减,最高衰减幅度达33.3%。研究还发现亥姆赫兹共鸣器的脉动衰减作用具有很强的频率选择特性,且安装于主管路的不同共鸣器共振频率互不干扰,在阀腔安装2个共鸣器能够同时有效衰减2、4倍频的压力脉动,而对其它频率脉动不产生影响。     

新型电梯滚轮导靴

针对目前高速住宅电梯滚轮导靴引起的电梯振动和电梯噪声的投诉,提出了一种新型宽频降噪高寿命的电梯滚轮导靴。加入聚四氟乙烯材料层,利用其摩擦因数低、耐磨性好等特点,降低噪声,延长其使用寿命,中间设置橡胶层,减缓径向受力,降低振动。滚轮上增设小孔,利用亥姆霍兹小孔吸声原理在滚轮上形成共振腔,以达到降低运行噪声的作用。设计简单,制造成本低,具有工程应用意义。     

临床应用方形与圆形亥姆霍兹线圈对比研究

为了实现胶囊机器人临床应用,需要设计一种大尺寸的三轴亥姆霍兹线圈,根据圆形和方形亥姆霍兹线圈的结构与物理特性,建立满足人体容纳空间的三轴亥姆霍兹线圈电磁模型,分析了空间磁场的均匀度。以总视在功率为目标函数,通过序列二次规划法对方形和圆形线圈结构参量进行优化和对比,研究结果表明:在中心磁感应强度、内部有效容纳空间和通入交流电流相同时,方形线圈总视在功率最低、均匀度更高,易于装配,总体性能更好。     

Measurement of the sunroof buffeting noise with an automatic deflector-traversing device

A wind deflector that is properly installed near the leading edge of the sunroof opening of a vehicle is known to effectively suppress the sunroof buffeting noise. However, the efficiency of wind noise reduction is very sensitive to the position and angle of the deflector. An automatic deflector-traversing device was devised to automate the sunroof deflector test procedure. It can automatically place a deflector at any desired position and angle with high accuracy. The deflector-traversing device was tested in a SUV vehicle at various wind speeds in an acoustically treated wind tunnel. In the test reported in the present work, the investigation area within which the position of the deflector could be varied was approximately 12mm × 20mm. Hundreds of deflector positions and angles were tested in the investigation area in a relatively short time period. A post-processing program was then used to process the abundant data obtained from the automatic measurements. For a narrow region of investigation, the post-processing program yielded color maps with high resolution for the high-frequency wind rush noise levels as well as the low-frequency sunroof buffeting noise levels as functions of the positions and angles of the deflector. It is concluded that the deflector-traversing device can be used together with an analytical model for the prediction of the buffeting noise for optimizing the deflector position to effectively suppress both the buffeting noise and the wind rush noise.     

汽车风振噪声的空气射流结构优化

风振噪声的控制研究目前是汽车领域的研究热点与重点之一。通过数值模拟分析研究了空气射流方法对风振噪声的抑制效果。运用大涡模拟(LES),引入更加准确有效的声品质评价参数,分别对天窗和右后窗的空气射流结构进行优化分析,得到了最优结构参数结果。仿真结果表明,空气射流结构对风振噪声的抑制效果显著。     

基于GA-BP的汽车风振噪声声品质预测模型

目前对于汽车风振噪声的优化研究主要以声压级（Sound pressure level,SPL）作为单一评价指标,既不能全面反映噪声的物理属性,也无法考虑人耳对噪声的主观认知过程。为准确评价风振噪声,引入声品质,运用大涡模拟（Large eddy simulation,LES）对风振噪声进行数值仿真,根据实车道路试验判断仿真的准确性;对仿真结果进行声品质客观评价与主观评价,综合声品质客观评价参数与声品质主观评价试验结果建立BP神经网络预测模型;利用遗传算法（Genetic algorithm,GA）,进一步对BP神经网络的结构参数进行优化,建立GA-BP声品质预测模型。研究结果表明,GA-BP声品质预测模型在训练速度和预测精度上都优于BP神经网络预测模型。预测模型基于声品质主客观评价结果,其预测值可以代替传统的声压级评价指标,为风振噪声提供更为准确合理的评价。     

环面节流平面气浮轴承大间隙下流场数值模拟

利用三维粘性可压缩平均Navier-Stokes方程,采用SSTk-ω湍流模式,使用非结构化网格和二阶精度的有限体积法,对环面节流圆盘推力轴承大间隙下的流场进行了数值模拟并与层流模式数值结果、实验进行了对比,结果表明,SSTk-ω湍流模式数值模拟的压力分布与实测的压力分布符合程度比较高。马赫数和速度数值计算结果表明,流场内存在激波和激波边界层的相互干扰,导致壁面边界层流动出现了分离,压力出现激烈变化。     

基于CFD/CA的离心泵流动诱导噪声数值预测

基于Lightill声类比理论,采用计算流体力学(Computational fluid dynamics, CFD)和计算声学(Computational acoustics, CA)相结合的算法对离心泵内部声场进行求解。基于SST k-ω湍流模型封闭雷诺时均方程,对离心泵内流场进行三维非定常计算。在流场计算的基础上采用边界元法对叶片偶极子源和蜗壳偶极子源的辐射声场进行求解,研究了蜗壳振动对声压级分布的影响,并搭建试验台对所提出的算法进行验证。结果表明,叶频及其倍频是流动诱导噪声的主要频率,隔舌附近监测点的压力脉动强度最大;声振耦合作用对声压级分布的影响不可忽略,模态振型所在的频率(580 Hz)下声振耦合作用的影响较大;泵出口场点的声压级比进口大,且均在叶频处最大,效率最高的工况点声压级最小;声场模拟和试验结果在趋势上基本吻合,最大相差3.1%,肯定了所提数值算法的预测作用,可为离心泵低噪声优化设计提供参考。     

高压下环面节流静压气体轴承适用的润滑方程探讨

采用纯黏性润滑方程和基于层流模式、SST k-ω湍流模式的N-S方程,对环面节流静压气体润滑推力轴承内的压力分布进行了研究,分析了随着气膜厚度的变化,轴承流场内压力的变化及其变化机理。实验证明,在轴承厚度很小时两种方程求得的压力值与实验结果一致,然而随着气膜厚度的增大,采用纯黏性润滑方程计算所得结果的偏差很大,而采用N-S方程计算所得结果与实验结果基本一致,但在逆压力梯度段存在偏差;SST k-ω 湍流模式能较好地处理湍流剪切应力在逆压梯度边界层内的输运和激波与边界层的相互作用,准确模拟出气膜入口附近复杂的流动状态。      

Comparison of DNS and Reynolds stress modelling of flow around a rotating cylinder

The low Reynolds number stress-omega model is applied to flow associated with a rotating cylinder operating in a larger, stationary cylinder. The working fluid fills the gap between the cylinders. Direct numerical simulation data are used to test the predictions by this turbulence model. Previous work has shown that simpler models are unable to predict with reasonable accuracy the wall shear stress experienced by the rotating cylinder. The present study with a more complex turbulence model shows that the wall shear stress on the rotating cylinder is underestimated significantly. Examination of turbulence velocity fluctuation intensity distributions points to underprediction of the streamwise turbulence level and excessive values of the wall normal turbulence level. Results are given for no shear and a wall shear at the outer cylinder surface but no effect on the inner cylinder statistics was found. An examination of the Reynolds stress anisotropy tensor components highlights a significant deficiency in this parameter which is an essential component of the pressure-strain modelling of Reynolds stress models. The most significant aspect is a rapid decrease of the streamwise component of the Reynolds stress anisotropy tensor relative to the direct numerical simulation results and values which are too low for the other two components.     

Three-dimensional effects of supersonic cavity flow due to the variation of cavity aspect and width ratios

Unlike the steady closed-type supersonic cavity flow, open-type cavity flow is divided into internal and external flows by turbulent shear layer. The cavity flow may cause resonance phenomena due to pressure oscillation, depending on the cavity geometry and the flow conditions. These phenomena may induce noise generation, structural damage, and aerodynamic instability. In this research, the flow characteristics of three-dimensional supersonic cavity flow of Mach number 1.5 were analyzed with the variations of aspect ratio and width ratio. Three-dimensional unsteady compressible Reynolds-averaged Navier-Stokes (RANS) equations were used with a turbulence model. For numerical calculations, the 4th-order Runge-Kutta method and the FVS method with van Leer’s flux limiter were applied. The numerical calculations were performed by using a parallel processing program with 16 CPUs. The sound pressure level (SPL) spectra of pressure variations were analyzed at the point of cavity leading edge. The correlation of pressure distribution (CPD) was also analyzed for the propagation of dominant oscillation pressure waves with respect to the reference point of the cavity leading edge. The dominant oscillation frequency was compared with the oscillation modes of Rossiter’s formula. Oscillation Mode 2 appeared as a dominant oscillation frequency regardless of the aspect ratio of cavity in the two-dimensional flow. Oscillation Modes1 and 2 appeared in three-dimensional cavities of small aspect ratios. However, as the aspect or the width ratio increases, only the mode 2 or 3 frequency appeared as a dominant oscillation frequency.     

风切变对风力机尾流湍流特征影响的研究

采用LES方法,对自行开发设计的100 W小型水平轴风力机在有、无风切变两种入流情况下的尾流特征进行了模拟计算,计算中提取了流场稳定后的x、y、z三个方向的瞬间速度、压力等参数的600个数据样本,计算得到了尾流内轴向速度和湍流强度的方均根值,分析了有、无风切变两种入流情况下风力机尾流内的时间平均轴向速度、湍流强度及涡结构等流动特征。结果表明:无风切变入流情况下,尾流内的叶尖涡、中心涡及轴向速度都呈现对称性;而风切变入流情况下,尾流内叶尖涡螺旋轨迹上面部分的螺距明显大于下面部分的螺距,呈现出了非对称性,而中心涡和轴向速度也都呈现出一定的非对称性,且风切变入流情况下尾流内的涡传播距离更远;在y/d6的近尾流区域内,无论入流是否存在风切变,风力机尾流膨胀现象都不很明显;在相同入流湍流强度条件下,有、无风切变入流情况下尾流内湍流强度的变化规律相似,入流风切变对尾流内湍流强度的影响较小。     

On the influence of the characteristics of flow on pressure distribution around building models with a view to simulating the minimum height of the atmospheric boundary layer

Results of an investigation of the influence of the characteristics of flow on pressure distribution around building models are reported. The influence of the mean velocity profile, turbulence intensity, percentage boundary layer immersion ratio and the building model's aspect ratio on the pressure distribution was studied with the view of simulating the minimum height of the atmospheric boundary layer in a wind tunnel for building aerodynamics investigations. It is cautiously suggested that atmospheric boundary layer height of at least three times the building height should be simulated in the wind tunnel. Turbulence characteristics exercise primary influence on the flow around models and shear exercises secondary influence on the flow. Finally, it is imperative to simulate the correct turbulence intensity and scale in the simulated turbulent boundary layer. However, further tests should be carried out to study these problems in closer detail.