Blade passing frequency (BPF) noise is the dominating component of the flow induced noise of centrifugal fans. The numerical methods for BPF noise prediction, based on the computational aeroacoustics (CAA), have been published for decades. However, there are a couple of challenges for accurately predicting noise for industrial centrifugal fans. The first arises from the fact that the free field hypothesis, adopted in the numerical model, has not yet been carefully studied. The second challenge stems from the current criteria for which the prediction results are compared to the measurement data. Because the test conditions do not always satisfy the requirements of the numerical model, inaccurate predictions occasionally resulted. Therefore, since the prediction results may deviate largely from the test data, the applicability of these methods is severely limited.

为了识别企业作业环境中的高噪声作业区域和控制职业噪声的危害,本文基于噪声监测和噪声预测方法,绘制了企业作业场所的噪声分布图,并在此基础上研究了区域内噪声性听力损失的危害状况及高危人群的典型特性.结果表明:以大于80 dB(A)作为划分高噪声作业区域基本涵盖了职业噪声危害的区域;实例分析显示高噪声作业区域约38.46％的作业工人患有噪声性听力损失,其中年龄为35～50岁、工龄10a以上的作业工人是语频段听力损失的高发人群.

通常认为圆弧叶片的加工简单,但流动性能差,在后向离心风机已很少应用, 但近来发现,有些圆弧叶片能有85％以上的整机全压效率.为此,本文对4个不同型号的后向离心风机采用圆弧叶片和现在常用的等当量扩张角流型叶片进行整机性能数值预估对比,结果表明:上凸圆弧叶片性能良好,但下凹圆弧叶片性能差.

A statistical model was established in this article for predicting the broadband turbulent noise of axial flow fans. First, an integral formula was deduced based on the Ffowcs Williams-Hawkings (FW-H) equations for the purpose of calculating the sound power spectrum of aeroacoustic sources with low rotating speed. The auto-correlation spectrum of the fluctuating pressure on the fan blades was modeled by a two-section exponential function. The characteristic aerodynamic parameters, such as boundary layer thickness, external flow velocity, wall shear stress, and average static pressure gradient on blade surfaces, were obtained by solving the steady Reynolds-averaged Navier-Stokes equations and used to normalize the auto-correlation spectrum. Then, the unknown coefficients in the exponential function were determined by fitting the experimental noise spectra for two typical and commercially available axial flow cooling fans. Finally, under the conditions of retaining the similar aerodynamic performances of the two baseline fans, a new fan design was developed and optimized using this method, of which the overall noise level was 2 dB lower than the quieter of the two baseline fans. The predicted noise spectra for all three fans agreed very well with the experimental data.

<正>噪声是工业企业作业场所中最普遍存在的有害物理因素之一,噪声不仅影响作业工人的生产效率,而且危害工人的身体健康,工人长期接触高强度的噪声会形成永久性的并且不可恢复的听力损失。在国外,听力损失是最主要、最常见的职业病之一,而在我国已有上百万的工人患有听力损失。

结合风机性能数值预估与实测数据,分析了3个小比转数离心风机系列的气动设计,发现最佳效率工况点流量均向大流量区有较大偏移.根据数值试验,适当减少原定的设计流量值,得到最佳效率点的流量值和原设计流量值吻合,并且性能良好.

The core of road traffic noise prediction lies in the establishment of the noise source intensity of traveling vehicles. European and American countries have carried out a lot of research work in this area and got lots of practical results. However, in the domestic of China, common vehicles are not exactly the same with that of developed countries in Europe and the United States. Therefore, the noise source characteristics are inevitably different from each other. More than 6000 cars in Beijing has been tested in this research and then analyzed and summarized several vehicle noise source intensity characteristics. After that, we put forward to a vehicle noise source intensity model which is suitable for drawing traffic noise map of major cities in China.

针对某型轿车发动机进气系统的空气滤清器,建立了声学三维有限元流体预测模型,采用先测量滤纸声学参数,再与滤清器空腔关联计算的分析方法,计算分析了其声学消声效果.与实测结果比较表明,此种模型和分析方法具有较好的预测准确性.此外,分析也发现滤纸等因素对滤清器的消声效果也具有不同程度的影响.

介绍了通风消声器的评价指标,对检测数据和检测方法进行了分析,讨论了评价插入损失、阻力系数和再生噪声过程中存在的问题,提出了改进建议,以提高各实验室检测数据的实用性和可比性。

Traditional Micro-Perforated Panel(MPP) requires small diameter of holes over a very thin panel to obtain better property of sound absorption.In the case of constant hole rate,property of the sound absorption will become worse when panel thickness is increased.To avoid this problem,a new structure of MPP is provided.Different from the traditional MPP,cross-sections of holes of this MPP change suddenly in some places along the axes of the holes.In this paper,based on Ma's theory,an assessment of sound absorption properties of this kind of MPP is presented.Computation results and experimental data of an impedance tube are compared each other.It is found that the performance of absorption of this kind of MPP depends mainly on the portions of the small holes,and the portions of large holes are for increasing the thickness of the plate only.With this method,the sound absorption of the MPP can be kept in a better level when the thickness of the panel is increased.

对某商用对旋轴流通风机设计工况附近多个工况,分别采用单通道定常流和整机非定常流模型进行了气动性能的数值预估,并和实测结果对比,探讨了这两种数值模型用于对旋轴流通风机气动性能预估的可行性.

With the development of technology, phone has turned to be the essential communication facility. Phone′s ring is effective to remind people, but also annoys others. This paper investigates several parameters of the rings, including format, frequency, environment affection and sound quality, analyzes the characteristics of high annoyance phone′s rings by acoustic and non-acoustic way, and provides some helpful suggestion on reducing the annoyance.

<正>中华人民共和国环境保护部于2008年4月28日下发了"关于批准组建国家环境保护城市噪声与振动控制工程技术中心的通知"(环函[2008]42号),正式批准以北京市劳动保护科学研究所(以下简称劳保所)为依托单位建设"国家环境保护城市噪声与振动控制工程技术中心"。

介绍了某名牌空调室内机的声场测量方法,并通过对其噪声源进行分析,识别出风舌噪声、结构振动噪声和宽带噪声,并对其分别进行了说明.

奥运交通规划总体目标 奥运交通规划制定的总体目如下: 第一, 为所有参与者提供高效、安全、可靠的交通服务;

A blade force model used to predict the noise spectrum for low-pressure axial fans has been improved. The improvements include that the blade lift force distribution is given out by the 3-D numerical simulation for the fan flow field and the image part in Fourier extension for lift force should be remained. The prediction improved for noise spectrum of two model fans agrees with the measured data quite well.

The sound field radiated by noise sources in a cylindrical flow duct is so complicated that it has not yet been solved analytically. This paper presented a numerical method that was verified experimentally to predict the sound field. Figures are given for the direction coefficients of the sound pressure level (SPL) outside the duct for engineering applications. The figures can be used to easily calculate the sound power level of the sound source inside the duct through measuring the SPL at a single point outside of the duct. The sound field was numerically simulated using the linearized Euler equations, a fourth-order MacCormack finite difference scheme and Tam and Webb's non-reflection boundary conditions. The experiments in a semi-anechoic room used a scanning sound intensity meter to measure the sound power inside the duct and the sound pressure distribution outside the duct. The numerically determined SPL direction coefficients agree well with the measured data, with a maximum error within 1 dB.

首先给出吸气管道内噪声源辐射声场和管道入口流场的数值计算方法,再进行试验考核,最后给出辐射声压的指向性系数图.利用这些图就可方便地得到吸气管道内风机辐射声功率级和声压级的关系.