贯流风扇气动声场数值模拟及分析

针对贯流风扇气动噪声传播特性,采用基于非结构网格的CE/SE算法对其气动流场进行数值模拟,并模拟了气动噪声的传播.湍流模拟采用大涡模型,搭接式滑移网格模型处理动静干涉.噪声传播采用完全欧拉方程作为控制方程,远场采用无反射边界条件.将使用该方法得到的远场噪声频谱与实验数据进行对比分析,结果表明与实验测量得到宽带频谱不同,采用大涡模拟湍流模型进行声源模拟时,会加强部分离散频率上的声级,从而产生误差.     

双扬声器近场声源重放实验研究

该文针对电子器件散热用的一款变速轴流风扇的气动噪声及其降噪方法进行实验研究。首先利用风扇旋转轴等高平面内圆周分布的传感器阵列测量风扇不同转速下远场噪声分布,总声压级与转速的对数关系验证散热风扇主要气动噪声属于偶极源噪声,频谱分析显示离散单音噪声为主要噪声影响因素。基于管道声学理论的管道模态截止方法,研究进出风口安装圆形短管对风扇气动噪声的影响,实验结果显示不同位置、不同长度的短管对风扇远场噪声影响不同。额定转速下,在进风口安装2 cm管道可以使远场1 m处平均总声压级下降4.1 dB(A),降噪效果显著。模态测量结果显示,此种情况下对应离散单音处的风扇主要模态幅值大大降低,风扇离散单音噪声降低从而噪声总声压级大幅减小。该方法为散热风扇降噪提供了一种新的途径。     

低压头小流量轴流风扇气动噪声特性研究

本文提出了一套新的测试方法,能够获得全流量范围内低压头小型轴流风扇的气动和噪声性能曲线。利用所设计的测试台完成了具有不同叶片轴向掠角、安装角的微型轴流散热风扇的气动-噪声特性测试,研究安装角和气动掠对风扇性能的影响。结果分析表明:不同安装角下,与原型风扇相比,当Q0.6 m~3/min时,前掠降低了风扇的全压、全压效率,提高了风扇的噪声,而后掠有助于降噪。     

实验研究贯流风扇气动噪声源特性

复杂流动系统中气动噪声源特性的研究是研究噪声传播及建立气动噪声模型的基础.本文采用实验的手段研究了贯流风扇的气动噪声源特性。实验在本底噪声为19 dB(A)的静音室中进行,采用高精度,高频响的声压传感器分别测量了室内机进口,蜗舌壁面,近叶轮出口,远场等位置的声压波动.对得到的原始压力脉动数据进行了快速傅里叶变换,基于FFT变换的联合时频分析,基于连续小波变换的联合时频分析.分别在时间域和频率域进行了不同测量点的对比分析。结果表明,实验机表现为明显的宽频噪声特性,其主要噪声源为流场中的涡流.基于连续小波变换的时频分析方法能更精确地表现信号的非定常特性,能对信号进行不同层次的深入分析,得到更精确的结果.     

掠动叶对微型轴流风扇气动-声学性能的影响研究

轴向掠是叶片的径向成型方法之一.本文基于Fluent软件分别对具有前10°、后掠10°和径向0°动叶的三种风扇模型进行了定常流场和非定常流场的数值模拟,然后基于FW-H积分完成了风扇流动噪声的远场辐射计算,研究动叶的轴向掠对小尺寸轴流风扇气动与声学性能的影响.结果表明,前掠叶片和后掠叶片使风扇的全压在大流量工作区域低于0°径向风扇,内效率也略有降低.在气动声学性能方面,研究结果表明前掠不利于本文所研究的微型轴流风扇气动噪声的抑制,但后掠动叶降低了风扇的噪声,相比径向风扇,后掠风扇的远场噪声总声压级约下降1. dB.     

使用多孔蜗舌的贯流风机

将贯流风机的蜗舌替代为多孔板与容腔组合的结构,定性地研究其控制气动噪声的可行性。通过对气动特性和辐射声信号的实验测量,结合内部流场的非稳态雷诺平均数值模拟,分析了这种蜗舌改造对贯流风机的整体特性和内部流动特征的影响,结果表明多孔蜗舌对贯流风机的压力-流量曲线作用并不明显,但对风机的噪声有着重要的影响,改变蜗舌迎风面的穿孔率可以有效地控制贯流风机的噪声。     

转速对弯掠轴流风机气动噪声的影响分析

针对弯掠轴流风机气动噪声问题,采用大涡模拟(LES)和基于Lighthill声类比的FW-H模型相结合的方法进行非定常计算,通过快速Fourier转换(FFT),得到风机远场气动噪声声压级分布。对比研究了三种转速下旋转区内声压级分布规律、时域及频域特性,结果表明:旋转区域内声压级随转速增加而增大,前缘分离涡在某一转速时影响区域和强度最大;在一个旋转周期内,声压脉动呈现出6个波峰与波谷,验证了叶片转动频率是风机内部气动噪声的主要激励频率.     

大小叶片贯流风机内流特性分析与实验研究

为降低空调用贯流风机的噪声,改善音质,通过采用直叶片贯流风轮达到斜扭叶片贯流风轮的音质和低噪声特性,从而降低贯流风轮的制造成本,本文设计了大小叶片交错组合的新型非等距贯流风机,并采用滑动网格对其内流特性进行了非定常数值模拟,同时对其气动噪声特性进行了实验研究.大小叶片贯流风机的偏心涡基本稳定在叶轮中心与蜗舌相连的切线上,位于叶轮内圆周附近.风轮非定常运转时,偏心涡的涡核位置在直径为2mm的圆所围成的区域内变化.大小叶片交错组合的贯流风轮改变了叶轮与蜗舌的间距,有效地降低叶片通过频率噪声并改善了音质.采用大小叶片交错组合的贯流风轮能够达到斜扭叶片贯流风机的降噪效果.     

贯流风扇偏心涡非定常特性研究

本文应用大涡模拟计算并描述了贯流风扇内部旋涡流动的非定常变化细节.研究结果表明,贯流风扇叶片绕流流态复杂,吸力面存在分离流动,叶片出口形成明显的尾迹区.在蜗舌一侧存在偏心涡,由核心区域和外围区域组成.其中偏心涡的核心区域由两至二三个叶道内气流在内径处分离产生的旋涡团组成,在流动过程中涡量由上游的脱落涡得到补充.偏心涡的外围区域由蜗舌附近回流的旋涡团组成,引起蜗舌表而压力脉动,产生干涉噪声.干涉噪声频谱在低频带上具有较大声压级,最大声压级处的频率和叶轮出口侧叶道的脱落涡频率相关.     

贯流风机内动静干扰发声机理的研究

本文通过实验与数值计算方法,探讨了贯流风机内动静干扰的现象及其诱导的噪声特性.文中给出了贯流风机流场的三维大涡数值计算结果,分析了声源场的特性,指出贯流风机流场具有较强的随机性。分别对直叶轮及斜叶轮气动性能及远场噪声进行实验测量,讨论了两种叶轮的优劣性。使用微压传感器对蜗舌出口处边界层压力脉动进行采集,给出了此处边界层辐射噪声源的相关分析.通过对实验结果分析指出声源脉动的宽频特性是被测风机噪声呈现宽频的主要原因。     

尾缘凹陷轴流风轮内流特性分析与降噪研究

为减少空调室外机用低压轴流风轮叶片的颤振,改善音质,降低噪音和电机功率。本文设计了尾缘凹陷新型三叶轴流风轮,同时除对前缘局部加厚处理外,对叶片其他区域整体减薄。文中采用Navier-Stokes方程对新风轮和原风轮的内流及气动特性进行了三维数值模拟,同时对两者的流量压力曲线和噪音频谱进行了实验研究。研究表明:对轴流风轮叶片尾缘进行凹陷设计,对前缘以外的区域减薄设计,能够减轻风轮重量,降低电机负荷同时减弱转子尾迹;对叶轮前缘进行局部加厚处理可以减小叶尖颤振,降低叶片旋转频率峰值噪音,从整体上降低噪音,改善音质。     

基于蜗舌改型的空调用离心风机流动分析及降噪研究

本文采用计算流体动力学和声类比相结合的混合方法对空调用离心风机进行流场以及声场的计算,同时进行风机风量和噪声的实验测量,验证所采用的数值计算模型和计算方法的有效性.针对原型非常规蜗壳,提取蜗壳中间截面型线进行直蜗舌的蜗壳设计,在此基础上设计了三种倾斜蜗舌的蜗壳.根据数值计算结果,对最优倾斜蜗舌进行了实验验证。经实验测试,风机在各个工况点风量均有提升,在最大风量点风量提升6.0%,噪声降低1.4 dB(A).数值分析风机内部流动特征及噪声特性,发现在蜗舌附近流动区域内湍流强度和涡量明显减小,在叶片通过频率处声功率谱密度以及噪声峰值明显下降,这也表明风机的旋转噪声得到了有效控制。     

An investigation into the noise generation of CPAP devices: Experimental and numerical study

Continuous positive airway pressure (CPAP) devices are popularly used for obstructive sleep apnoea (OSA) treatment. However, the noise level emission from these devices has been identified as a potential factor for patient’s discomfort and rejection. There is a need to obtain information on the noise characteristics and source locations in order to tackle the most serious noise source within these devices. A typical CPAP device was used for the investigation and its sound characteristics and sound power levels were determined. The noise generated from a centrifugal fan was also independently investigated to address its contribution to the overall noise of the device. Frequency analysis suggested that the noise generated from both the CPAP device and the fan is broadband in nature with discrete peaks containing rotational and non-rotational components. The broadband components were then studied in detail using numerical simulation approach. Computational aeroacoustics (CAA) method with hybrid approach was used to a three-dimensional (3-D) CPAP fluid model to predict the aerodynamic and aeroacoustics behaviours of the device. This showed a complicated flow structure involving flow separation, rotation, and vortices in several locations which resulted in high level of flow turbulence inside the device. The turbulent components were used to estimate the broadband noise level at source using the broadband noise source (BNS) models. It shows the most critical location is at the fan region and at the fan inlet.     

Shock associated noise of inverted-profile coannular jets,part II: Condition for minimum noise

An experimental and theoretical investigation of shock-associated noise of inverted-profile coannular jets is described. For a fixed fan-stream Mach number, it is observed that the shock-associated noise often drops suddenly to a minimum as the reservoir pressure of the primary jet increases. When this happens, the almost periodic shock cell structure of the fan stream is found to nearly completely disappear. In this paper, an analytical model of this phenomenon is constructed and studied. It is theoretically established that this sudden change in the shock structure and hence the decrease in shock associated noise would occur when the primary jet flow is just slightly supersonic regardless of the Mach number and temperature of the fan stream. This minimum shock associated noise condition is confirmed in several series of experiments.     

Visualization of aerodynamic noise source around a rotating fan blade

The purpose of this study is to understand the aerodynamic noise source distribution around a rotating fan blade by measuring the noise signal and velocity field around the blade. The local noise-level distribution over the fan blade is measured by microphone arrays, and the flow field is visualized by smoke and phase-averaged PIV measurement. The noise source distribution is examined by cross-correlation analysis between noise signal and velocity fluctuation. It is found that the noise source is located near the rotating fan blade, especially around leading and trailing edges. The separation and reattachment of flow are observed near the leading edge, and the tip vortices and vortex shedding are found near the trailing edge. The cross-correlation distribution of the noise signal and the radial velocity fluctuation shows large magnitude in the correlated regions, which indicates the noise generation by the formation of vortex structure around the blade.     

静子尾缘喷气后尾迹与动叶干涉噪声研究

尾缘喷气技术已经广泛地用于航空发动机和多级压缩机等领域,用以降低动静叶片间的相互干涉作用以提高透平机械的气动性能,并降低动静干涉噪声.本文对尾缘喷气用于低压轴流风机进行了详细的研究,对轴流风机的上游静叶实施尾缘喷气,通过实验测量,尾缘喷气使静叶尾迹达到无动量亏损尾迹状态能够降低风机噪声,文章还提出了基于CFD数值模拟的尾迹与动叶相互干涉的噪声预测模型,预测结果和实验结果比较接近.     

Flow-induced noise in a suction nozzle with a centrifugal fan of a vacuum cleaner and its reduction

Noise reduction in a vacuum cleaner with a brush nozzle for cleaning a bed blanket is investigated numerically in fluid dynamic aspects. Governing equations describing nonlinear flow fields in a suction nozzle are solved simultaneously. The components of a rotary fan, a brush drum, and a separation block are installed in the nozzle. First, flow patterns in the nozzle are analyzed and based on them, flow resistance is evaluated to find a primary noise source. Flow resistance induces the loss of a suction performance as well as noise generation. In the brush nozzle, the separation block and the rotary fan obstruct smooth air flow and result in high level of noise emission. The rotation of the fan itself affects little noise generation. From the numerical results, a method to reduce noise and maintain the suction performance is suggested. In this method, the suction performance is increased through the optimization of the separation block, which is attained by the modification of its shape. And then, the height of a fan blade is shortened, leading to the performance loss. At the cost of it, the sound power level of noise is reduced by 4-5 dB(A) and at the same time, the tonal noise and the sound quality are improved appreciably. The method has been verified by experimental tests. It is found that in the brush nozzle, flow resistance is critical in noise emission and accordingly, fluid dynamic approach to noise reduction is effective.