An improved prediction model of vortex shedding noise from blades of fans

The main source of the noise of an axial flow fan is the fluctuating pressure field on blade surfaces caused by the shedding of vortices at the trailing edge of blades. An analytical model to predict the vortex shedding noise generated at the trailing edge of blades of axial flow fans was proposed by Lee in 1993. In this model, for mathematical convenience, an idealized vortex street is considered. However, the agreement between the analytical results and the experimental data needs to be improved because of the simplification about the Karman vortex street in the wake of blade. In the present study, a modified model is proposed based on the prediction model by Lee. The boundary layer theory is used to analyze and calculate the boundary layer development on both the pressure and the suction sides of blades. Considering the effect of boundary layer separation on the location of noise source, the predicted overall sound pressure level compares favorably with the experimental data of an axial fan. In the calculation of A-weighted sound pressure level (L_A), considering the effect of static pressure on radiate energy, the predicted broadband noise with the modified model compares favorably with the experimental data of a multiblade centrifugal fan.     

Aero—Acoustics of Modern Transonic Fans—Fan Noise Reduction from Its Sources

The noise of aerodynamics nature from modern transonic fan is examined from its sources with the perspective of noise reduction through aero-acoustics design using advanced Computational Fluid Dynamics (CFD) tools. In particular the problems associated with the forward propagating noise in the front is addressed. It is identified that the shock wave spillage from the leading edge near the fan tip is the main source of the tone noise. Two different approaches have been studied to reduce the forward arc tone noise and two state-of-art transonic fans are designed using the strategies developed. The following rig tests show that while the fans exhibit other noise problems, the primary goals of noise reduction have been achieved through both fans and the novel noise reduction concept vindicated.     

柴油电站的降噪方案分析

对柴油机组的降噪方法、降噪结构及其效果进行了分析；分析了降噪特性曲线对消音器参数选择的指导作用。     

Laser structural training,artificial intelligence-based acoustic emission localization and structural/noise signal distinguishment in a thick FCEV fuel tank

Acoustic emission (AE) is present when transient elastic waves from structures are generated by various causes, such as structural cracks, fiber breakage, debonding of fibers and matrix, temperature changes, and fatigue. In AE-based structural health monitoring, the simple event counting method is unable to determine where AE occurs, so it is possible to discard a structure even if it is safe or not discard it when it is not safe. Much research on AE localization has been conducted to solve these problems. However, most of the methods have limitations with respect to isotropic material or near field conditions and cannot be applied when there is a change in the boundary conditions of the structure or obstacles. Thus, to solve these problems, a Q-switched laser capable of generating elastic waves has been used to scan and train the structures. Although this method worked effectively on thin specimens, a more advanced method is required for thick and complex structures, such as a fuel tank of a fuel cell electric vehicle (FCEV). Therefore, we propose a novel method based on artificial intelligence (AI) that can be applied to a real FCEV fuel tank fabricated with a filament winding composite. More specifically, this technique modulates the difference in characteristics between AE and laser-induced elastic waves in the frequency domain with AI. AE is simulated by a pencil lead break of the Hsu-Nielsen source. Then, AE localization is performed through cross-correlation in the time?frequency domains between a generated AE signal and modulated laser-induced signals obtained from AI. In addition, an experiment conducted to localize the AE that occurs at arbitrary points in real time confirms that AE localization can be performed within 2 s. Finally, an AI algorithm is proposed to distinguish between structural AE and unwanted noise to consider real-world applications and visualize the features of these two types of signals.     

Investigation of flow dynamics and decrease of vortex noise inside volute of centrifugal fans

The characteristics of three-dimension flow dynamics inside the volute of a G4-73No.8D centrifugal fan was simulated numerically using a computational fluid dynamics(CFD) technique. The generation, evolution, and noise of the vortex were investigated when cylinder-shaped and cone-cylinder-shaped anti-vortex rings were added separately. Numerical results showed that large-scale vortices were broken effectively and the flow fields inside the fan were more uniform with the two anti-vortex rings installed. Experimental results indicated A-sound level and spectrum noise of the refitted fan decreased and the two anti-vortex rings were effective in decreasing vortex noise. The cone-cylinder-shaped anti-vortex ring was more effective than the cylinder-shaped one in breaking large-scale vortexes and decreasing vortex noise. __________ Translated from Proceedings of the CSEE, 2006, 26(17): 117–121 [译自: 中国电机工程学报]     

Acoustic noise from tandem wind rotors of intelligent wind power unit

The authors had invented the unique wind power unit composed of the large-sized front wind rotor, the small-sized rear wind rotor and the peculiar generator with the inner and the outer rotational armatures without the conventional stator. This unit is called ＂Intelligent Wind Power Unit＂ by the authors. The front and the rear wind rotors drive the inner and the outer armatures, respectively, while the rotational torque is counter-balanced between both armatures/wind rotors. This paper discusses experimentally the acoustic noise from the front and the rear wind rotors. The acoustic noise, in the counter-rotating operation, is induced mainly from the flow interaction between both rotors, and has the dominant power spectrum density at the frequency of the blade passing interaction. The noise is caused mainly from the turbulent fluctuation due to the flow separation on the blade, when the rear wind rotor stops or rotates in the same direction as the front wind rotor.     

变频技术在泵与风机节能改造中的应用分析

某热电厂泵与风机等辅机上应用变频技术进行节能改造,取得年节电343.67万kWh的经济效益和较好的控制效果。用户应根据具体的管路特性曲线确定是否适用变频改造,并应了解一些使用变频器时的注意事项,以最大限度发挥变频器的作用。     

室内排水噪声的分析与控制探讨

室内排水产生噪声影响人们的日常生活,逐渐引起了人们的关注。主要对室内排水的噪声进行分析,从噪声源和传播途径两个方面分别对UPVC管和卫生器具这两大主要噪声源进行分析,指出降低硬聚氯乙稀（UPVC）管在排水时产生的噪声的最佳措施是采用UPVC螺纹管;对于卫生器具,宜采用消音式。从传播路径方面也提出了一系列措施。     

Performances and acoustic noise of micro multi-blade fan

In this paper, the performances and the acoustic noise of the traditional type micro multi-blade fan were investi- gated experimentally and numerically, to optimize the specifications of the fan for the resident circumstances. The acoustic noise level decreases but the efficiency deteriorates slightly with the increase of the blade number of the impeller. Besides, the acoustic noise decreases with the increase of the distance between the impeller outlet and the volute tongue, in accompanying with the increase of the input and the deterioration of the fan efficiency.     

某发动机前端轮系张紧器异响分析及改进

针对某发动机前端轮系张紧器在特定转速下的异响问题,通过仿真与试验,分析异响产生原因并进行结构优化.对张紧器进行模态仿真分析,发现张紧器螺旋弹簧的一阶轴向伸缩变形模态频率为347 Hz,与理论计算的异响转速相关频率(344 Hz)非常接近.拆解发生异响的张紧器,发现张紧器第二圈弹簧与壳体底部卡槽凸台发生干涉,产生摩擦噪声...     

基于ARMA模型的变压器噪声逆向还原实验研究

基于声辐射理论和激光测振原理,通过实验测量干式变压器模型的表面振速和辐射噪声声压,分别采用表面振速法和频响函数法求得变压器的声辐射指数。在此基础上,采用自回归滑动平均（ARMA）模型开展变压器噪声逆向还原研究,获取声压与声压级预测值,并与实验值进行对比。结果表明：采用频响函数法得到的声辐射指数比采用表面振速法得到的约大1.0 ～ 1.5 dB;采用基于ARMA模型的噪声预测算法得到的声压与实验得到的声压约相差0.015 Pa,声压级约相差1 dB;利用基于ARMA模型的预测算法和激光测振原理进行噪声逆向还原具有较好的可行性,且可推广应用于其他结构辐射噪声的预测。     

摩托车加速噪声自动测试系统的实现及通过噪声特性分析

摩托车加速噪声自动测试系统是先进的车辆通过噪声测试手段,实现了对加速噪声相关数据准确完善地测量、存储及分析。本文经过大量分析加速噪声测试过程试验数据,确定发动机转速是影响摩托车噪声的最重要因素。通过建立加速噪声声学模型,深入分析加速噪声测试时传声器测点声压级变化规律,明确了确定加速噪声最大声压级对应车辆工况的方法及意义。     

浅析DF4型机车起动变速箱噪音问题

就机车检修及运用中经常出现的起动变速箱噪音大或异音现象,从变速箱内外两方面进行了分析,并提出了设计、检修中应注意的因素及改进建议。     

基于独立分量分析和时频分析的柴油机燃烧噪声研究Ⅰ:燃烧噪声分析

燃烧噪声是柴油机最主要的噪声源之一,重点研究基于独立分量分析的燃烧噪声分离.首先针对柴油机噪声成分的复杂性,应用FastICA方法从噪声测试信号中分离了源信号分量,应用峭度检验了柴油机噪声信号的非Gauss性.根据时间信息识别了燃烧噪声和喷油噪声等独立分量.其次针对噪声信号的非平稳性,研究基于小波尺度谱噪声分量的时频特征分析.针对试验工况下的独立噪声分量,应用Morlet小波尺度谱在时频联合域内提取了各噪声分量的时频特征.     

静止介质中点声源远场噪声的数值预测

采用Kirchhoff方法计算点声源的远场气动噪声。Kirchhoff积分面为包围点声源的固定圆柱面,采用理论解析法得到圆柱面上的近场气动流场解,然后根据Kirchhoff积分公式求解远场声压信息。详细论述了将Kirchhoff积分公式程序化的循环累加法;并着重分析了不同积分面及其网格划分对积分精度的影响。     

内燃机车司机室噪声特性及吸声材料研究

通过对内燃机车的运行噪声测试和分析,确定了在不同运行速度、不同测试位置时的噪声分布规律及传播途径,并对吸声材料的吸声系数进行测量和分析,确定了理想的吸声材料。     

某火电厂引风机振动故障分析及解决措施

某火力发电厂对脱硫系统进行改造,在其中一台机组安装公用GGH低泄漏风机后的试运中,存在振动过大的故障。通过对该风机的振动检测,获取了包括振动趋势图、振动幅频图和振动相频图,结合振动信号的特征,对故障进行了诊断,得出了振动故障是由于引风机质量不平衡,通过加重处理后,引风机前后轴承的最大振幅由原来的接近500μm分别降低到了36μm和26μm,取得了显著的效果。     

Effect of boundary layer trip on reduction of jet noise in over-expanded nozzle flow

A flow resonance accompanied by the emission of acoustic tones occurs in an over-expanded convergent-divergent (C-D) nozzle when operated at comparatively low pressure ratios.This phenomenon is distinguished from conventional screech tones and is referred to as “transonic tones”.In contrast to screech tones,the peak resonant frequency for transonic tones increases with pressure ratio;the peak sound pressure level exceeds 110 dB.In this study,we investigated the basic characteristics of transonic resonance and tones using a circular C-D nozzle in an anechoic room.The effects of the boundary layer trip were also evaluated using a tripping wire for the suppressing transonic resonance and tones.The results of acoustic measurements show that several predominant peaks correspond to transonic tones.However,the boundary layer trip inside the nozzle effectively eliminated these tones and suppressed the unsteadiness of the flow inside the nozzle.     

Localization of wind turbine noise using a microphone array in wind tunnel measurements

An experimental investigation on scaled wind turbine models in a wind tunnel with a microphone array is presented. Our study focuses on the localization and quantification of aerodynamic noise sources on rotating wind turbine blades with the aim of identifying the contributing factors that have an impact on the source spectra. Therefore, wind tunnel measurements were conducted for three different blade geometries (NACA 4412 shape, Clark-Y shape, and sickle shape), five pitch angles between ?2° and +8° and five wind velocities between 5 and 13 ms^??1. For the localization of rotating sound sources with a microphone array, a rotating beamforming method based on the acoustic ray method is used. The Clean-SC deconvolution method was used to improve the resolution of the acoustic sources, and integrated spectra were calculated for the individual blades. The sound sources were localized at the wind turbine blades and assigned to the leading edge and trailing edge subregions. The results show a high dependency on the sound source distribution and the source strength with regard to the observed one-third octave bands, wind velocity, and blade geometry. Hence, the localization of rotating sound sources with a microphone array is a suitable method for the development of wind turbine blades that emit less noise.     

阶次分析在发动机进气噪声研究中的应用

进气噪声是发动机主要噪声源之一.为研究发动机转速对进气噪声的影响,采用阶次分析方法对一台车用四缸发动机的进气噪声进行了试验研究,首先分析进气口总声压级随转速的变化关系,并根据进气噪声阶次分析的特征分量分布,初步识别了其主要频率成分及相应噪声源,以及最大噪声产生时的发动机运行工况,分析结果可为发动机进气系统优化设计及噪声控制提供一定的参考依据.