Acoustic and aerodynamic design and characterization of a small-scale aeroacoustic wind tunnel

The aeroacoustic wind tunnel at Brandenburg University of Technology at Cottbus is a newly commissioned research facility for the experimental study of sound generation from bodies immersed in a fluid flow. The paper discusses the design criteria for the open jet wind tunnel that provides a maximum wind speed of 72 m/s at continuous operation and may be operated with nozzles of different dimension between 35 cm diameter (circular nozzle) and 12 cm by 14.7 cm (rectangular nozzle). Experiments may be performed either in a reverberant or in an anechoic environment. Both the aerodynamic and the acoustic design of the wind tunnel components are discussed in detail. Background noise measurements in the completed facility revealed very low levels comparable to other wind tunnels. The results of aerodynamic wind tunnel calibration confirmed a uniform flow quality in the jet and a very low axial turbulence intensity which is less than 0.2% for the 35 cm nozzle and less than 0.1% for the other nozzles. A final benchmark is provided by results of successful trailing edge noise measurements on an SD7003 airfoil that are presented and compared to results from the literature.     

机动车空气动力测试风洞的声学设计

测试、鉴定并研究高速机动车对环境及在车内所产生的噪声，必须有“安静”的风洞，抑制风洞内的气流噪声，将它的本底噪声降低到车辆噪声以下，测试大厅中有足够低的以上获得应有的自由声场范围，所有的声学处理措施不影响风洞的空气动力性能；吸声构件中不含矿物性纤维材料；具有相应的阻燃性能并易于清洁，本文介绍了满足以上所有要求的斯图加特大学空气动力实验室风洞的声学设计和所采用的新型吸声材料，给出了构造大样及实测结果     

大型航空声学风洞消声室建设与校测

风洞试验是进行民用飞机机体噪声研究的重要手段。为了满足航空飞行器低噪声设计在大型风洞中进行气动噪声试验的需求,中国航空工业空气动力研究院建设了FL-10大型低速风洞全消声室。通过在FL-10风洞试验大厅壁面安装吸声尖劈、对洞体外表面进行声学处理、对支撑系统进行隔声处理、对消声换气窗进行降噪处理等手段,建成了气动噪声风洞试验所需的声学环境。按照国家标准中给定的方法,利用张线方法实现了校准声源的布置,测量了消声室内沿不同路径、不同频率噪声的衰减规律,表明FL-10风洞消声室自由场特性达到了相应标准的要求,为后续在该风洞中进行大尺寸机体模型噪声试验奠定了基础。     

Design and performance of an open jet wind tunnel for aero-acoustic measurement

This paper presents the design and performance of an open jet, blow down wind tunnel that was newly commissioned in the anechoic chamber at the ISVR, University of Southampton, UK. This wind tunnel is intended for the measurement of airfoil trailing edge self-noise but can be extended to other aeroacoustic applications. With the primary objectives of achieving acoustically quiet and low turbulence air jet up to 120 m/s through a 0.15 m × 0.45 m nozzle, several novel noise and flow control techniques were implemented in the design. Both the acoustical and aerodynamic performances of the open jet wind tunnel were examined in detail after its fabrication. It is found that the background noise of the facility is adequately low for a wide range of exit jet velocity. The potential core of the free jet is characterized by a low turbulence level of about 0.1%. Benchmark tests by submerging a NACA0012 airfoil with tripped and untripped boundary layers at 0° and 10° angles of attack respectively into the potential core of the free jet were carried out. It was confirmed that the radiating airfoil trailing edge self-noise has levels significantly above the rig noise over a wide range of frequencies. The low noise and low turbulence characteristics of this open jet wind tunnel are comparable to the best facilities in the world, and for its size it is believed to be the first of its kind in the UK.     

叶栅风洞控制方法分析与实现

为解决叶栅风洞气罐容量小气源压力下降快给流场控制带来的难题,采用动态变参数和积分分离PID控制算法实现了叶栅风洞流场快速稳定和目标压力高精度控制目的;以调压阀后压力为控制点,采用叶栅入口压力误差值对控制点压力进行修正的方法,解决了常压和增压试验中控制滞后问题;变参数PID控制和选用具有确定对应关系控制点并对实际误差进行修正的方法,对小型暂冲风洞高精度压力控制和滞后问题的解决具有一定借鉴意义。     

基于PSD的风洞模型姿态角光学测量技术研究

开发了一种基于光电探测技术的风洞模型姿态角光学测量技术,实现了对姿态角的精确、实时、非接触测量。对激光探测头、模拟试验平台进行了优化设计,编写了功能齐全的实验软件,模拟了风洞试验运行实况,深入开展了一维和二维角度测量实验和分辨率测试实验。实验结果表明,该技术可对模型变化角度进行实时精确测量,测量范围达到了-10°～10°,测量精密度为0.0023°,测量准确度为0.0026°,分辨率可达到0.001°。该光学测量技术在风洞模型的角度测量和振动测量实验中切实可行,为测量风洞试验模型的姿态及振动提供了一种简洁有效的测量方法。     

风洞模拟等离子体绕流场回波频谱调制特性实验研究

目标以极高速度在大气层内运动时,周围会因剧烈摩擦产生等离子体绕流场.等离子体绕流场运动速度分布不均匀,而且绕流场电子密度随时间动态变化,导致等离子体绕流场对入射其中的电磁波产生不均匀的频率调制,进而影响雷达的探测性能.为了复现等离子体绕流场在电磁波照射时产生的不均匀频谱调制现象,本文在中国科学院力学研究所JF-10风洞开展了等离子体绕流场回波频谱测量实验,通过信号源、环形器、天线和频谱仪组成的测量系统,以点频发射体制,获取了S和C波段的回波频谱数据,观察到了等离子体绕流场对目标回波频谱的调制现象,对测量现象的形成原因进行了讨论;基于测量数据,仿真分析了等离子体绕流场对目标一维距离像的散焦效应.     

Evolution of downsized crescent-shaped dune in wind tunnel experiment

The migration of a downsized crescent-shaped dune was investigated in a wind tunnel experiment.Quantified upwind influx and vertical oscillation of the sand bed were introduced to modulate the saturation level of the sand flux above the dune surface to affect dune evolution.The evolution was recorded by top-view photography and then abstracted as the evolution of self-defined characteristic quantities using a digital image processing algorithm.The results showed that,in contrast to the case for spanwise quantities,the evolution of streamwise quantities corresponds to a linear increase in the modulation magnitude more positively and in a monotonic and convergent manner.In contrast with quantities on the windward face,the changes in quantities with respect to the horns were nonmonotonic with time and almost uncorrelated with the variation in modulation strength,which reveals the distinctiveness of leeside evolution.     

抑制风噪装置的实验

本文基于风噪原理提出了一种抗风噪结构设计,来抑制传声器拾取风噪。该设计由渐变管道和填充泡棉的腔体两部分组成。渐变管道用来降低气流流速,填充泡棉的腔体用来充当声屏障。COMSOL有限元仿真验证了渐变管道降低流速的能力,风噪实验证明了该设计能有效地抑制风噪。讨论了关键因素对该结构抗风噪能力的影响：大的腔体,小的渐变管道等效直径和高的泡棉密度,都有利于抗风噪效果。最后,基于声传输线和等效电路理论,建立了声波经过该抗风噪结构的传递损失模型。基于该模型和高频不失真条件,提出了抗风噪结构的尺寸设计指标。     

A procedure for the assessment of wind turbine noise

The noise assessment at the receivers due to wind turbines in operation is usually performed through outdoor measurements. Background noise and wind turbines noise (WTN) are related to wind speed and both contribute to the overall measured noise levels (environmental noise). Nevertheless, the relation between noise and wind speed is not easily predictable, especially when the wind farms are installed in hilly terrains, where the wind shear is truly remarkable. In Italy and in other countries, this kind of assessment is even more difficult to perform due to the national regulations that require to compute the difference between environmental and background noise levels with the same weather conditions. Thus, to get a reliable and approved measure of the residual noise it would be necessary to turn off the wind farm. This work suggests a technical procedure to simultaneously estimate the immission and the residual noise components measured nearby a wind farm when the residual noise is mainly generated by wind. This allows the evaluation of the noise impact produced by operational wind farms, without requiring the farm shut down. The method aims to be fairly straightforward, thus maintaining the required scientific basis to be used as an assessment procedure by consultants and public bodies.     

Aeroacoustic performance evaluation of axial flow fans based on the unsteady pressure field on the blade surface

Because of the European and global regulation concerning acoustic emission, the goal of manufacturers is to substantially decrease the noise radiated by turbomachines, and in particular axial fans, without degrading their aerodynamic performances. High rotation speed and increasing power add to the overall difficulties. The theoretical study of this paper consists of two parts: (1) an aerodynamic approach based on the vortex surface method and (2) an aeroacoustic approach which mainly concerns the prediction of the tonal noise using the Ffowcs Williams and Hawkings (FW-H) equation. One of the main goals is the evaluation of the unsteady aerodynamic forces applied on the fan blades. A 2D software analysis, based on the vortex surface method (or potential flow method), was carried out. That process enabled evaluation of the potential flow around a mobile grid; first in a steady mode, and secondly in an unsteady mode by introducing an upstream disturbance in the form of an inlet velocity variation. The sources of noise corresponding to the zones with high force fluctuation amplitude are located initially on the blade surface. These fluctuating forces are used to predict the tonal noise radiated by the fan in far field by means of the FW-H equation. Two axial flow fans were used in this study. The theoretical results will be compared to the experimental ones in order to evaluate the aeroacoustic performances of the fans.     

Modelling of icing of flying vehicles in climatic wind tunnels

Various forms of icing of flying vehicles are considered. Dimensionless parameters of similarity are chosen and justified. The necessity of creating a climatic wind tunnel for modelling the icing processes is grounded. A possible structural scheme of the climatic wind tunnel is given. It seems reasonable to develop a small-scale test bench for testing methods aimed at generating a uniform field of concentrations of supercooled droplets of a given size and for identifying the efficiency of various anti-icing systems and coatings.     

Amiet剪切层理论的角度折射验证研究

在开口射流风洞中进行气动噪声的定位测量试验时,射流边界的剪切层会对声传播产生折射影响。在处理过程中需要对传声器测量的信号进行剪切层修正,修正结果将直接影响到波束形成对气动噪声源定位的准确性。本文针对经典的Amiet剪切层修正理论,综合计算气动声学(Computational aeroacoustics,CAA)数值计算与试验测试,对该理论进行了验证,研究表明CAA计算与Amiet理论吻合,Amiet理论能够有效修正剪切层对声波的角度折射影响。     

低温风洞螺旋升降机热防护结构设计及性能分析

针对螺旋升降机的结构特点及低温风洞元件的工程防热要求,设计了不锈钢承压防护壳内置聚氨酯绝热层的三段式热防护结构。利用有限元软件建立了热防护结构数值模型,在低温风洞的低温与常温工况下进行了结构与传热分析,获得了热防护结构应力、变形及温度场分布情况。结果表明:热防护结构承受0.35MPa最大压差载荷时,其最大应力出现在防护壳中段与纵向加强筋连接处,经强度校核得到热防护结构在工作载荷条件下满足强度要求;热防护结构载荷系数为74.5(>3),一阶屈曲载荷为26.1MPa(>0.35MPa),热防护结构满足稳定性要求;低温与常温工况下,聚氨酯绝热层厚度为40mm,热防护结构内通入氮气流量分别为0.01kg/s和0.02kg/s时,螺旋升级机结构均处于263K-313K的安全温度范围内。     

激波风洞设施中的等离子体包覆目标电磁散射实验研究

利用JF10高焓激波风洞设施, 进行了等离子鞘包覆目标的电磁散射测量实验. 基于矢量网络仪的步进扫频体制, 在C波段进行实验, 观测到等离子鞘对目标雷达散射截面(radar cross section, RCS)的影响. 并且, 目标散射测量值中直接体现了激波风洞的高速气流状态信息: 气流前段会造成散射回波的剧烈变化且稳定性差, 持续0.5–1 ms; 激发的等离子鞘有效持续时间仅约为2 ms, 衰减了目标RCS回波.     

Analytical estimation of the noise due to a rotating shaft

This article focuses on noise prediction of a rotating shaft. The governing equations of motion for a Rayleigh beam, rotating about its longitudinal axis and subjected to a harmonic force, are first established using the Hamilton’s principle and Galerkin’s method. Then, the vibrating displacement of the shaft is solved for. The aeroacoustic theory, introduced by Lighthill and improved by Ffowcs Williams and Hawkings, is used for calculating the developed noise of the shaft in motion. The dominant effect to the noise is the surface pressure on the moving shaft. Parametric studies also presented. From the numerical data, the noise value, from a rotating shaft, corresponding to the higher significant resonance is greater than that related to the first resonant mode. This phenomenon has not been found in the frequency response of the shaft’s displacement.     

Design and performance simulation of a molecular Doppler wind lidar

A mobile molecular Doppler wind lidar at an eye-safe wavelength of 355 nm based on double-edge technique is being built in Hefei （China） for wind measurement from 10-to 40-km altitude. The structure of this lidar system is described. A triple Fabry-Perot etalon is employed as a frequency discriminator whose parameters are optimized. The receiver system is designed to achieve compactness and stability by putting in a standard 19-inch socket bench. Simulation results show that within the wind speed dynamic range of ±100 m/s, the horizontal wind errors due to noise are less than 1 m/s bdow 20-km altitude for 100-m vertical resolution, and less than 5.5 m/s from 20 km up to 40 km for 500-m vertical resolution with 400-mJ laser energy, 30-min temporal resolution, and a 45-cm aperture telescooe.     

风力机叶片气动噪声的影响参数

随着风力机的大型化发展,风电机组噪声对环境的影响不容忽视,必须对风力机气动噪声进行预测和控制。选取基于NACA、DU翼型的某风力机叶片作为研究对象,采用修正BPM半经验模型计算叶片的气动噪声特性,通过改变翼型族、弦长、机组运行状态、风切变指数、来流风向参数,研究叶片外形几何参数、机组运行工况对叶片气动噪声源的影响。计算结果从多个角度总结出水平轴风力机叶片气动噪声的变化规律,为开发高效低噪风电叶片提供参考。     

Barrier asymmetry and the mm-wave performance of resonant tunnel diodes

The effects of barrier asymmetry in a resonant tunnel diode (RTD) on the frequency response of the negative dynamical resistance are described for (i) DC biasing in the positive differential resistance (PDR) region and (ii) DC biasing in the negative differential resistance (NDR) region. Collector barriers more transparent than emitter barriers enhance performance for NDR DC-biased devices. Asymmetry has no apparent effect for PDR DC-biased devices operating in transit time mode.