Flap-edge aeroacoustic measurements and predictions

An aeroacoustic model test has been conducted to investigate the mechanisms of sound generation on high-lift wing configurations. This paper presents an analysis of flap side-edge noise, which is often the most dominant source. A model of a main element wing section with a half-span flap was tested at low speeds of up to a Mach number of 0.17, corresponding to a wing chord Reynolds number of approximately 1.7 million. Results are presented for flat (or blunt), flanged, and round flap-edge geometries, with and without boundary-layer tripping, deployed at both moderate and high flap angles. The acoustic database is obtained from a small aperture directional array (SADA) of microphones, which was constructed to electronically steer to different regions of the model and to obtain farfield noise spectra and directivity from these regions. The basic flap-edge aerodynamics is established by static surface pressure data, as well as by computational fluid dynamics (CFD) calculations and simplified edge flow analyses. Distributions of unsteady pressure sensors over the flap allow the noise source regions to be defined and quantified via cross-spectral diagnostics using the SADA output. It is found that shear layer instability and related pressure scatter is the primary noise mechanism. For the flat edge flap, two noise prediction methods based on unsteady-surface-pressure measurements are evaluated and compared to measured noise. One is a new causality spectral approach developed here. The other is a new application of an edge-noise scatter prediction method. The good comparisons for both approaches suggest that the prediction models capture much of the physics. Areas of disagreement appear to reveal when the assumed edge noise mechanism does not fully define the noise production. For the different edge conditions, extensive spectra and directivity are presented. The complexity of the directivity results demonstrate the strong role of edge source geometry and frequency in the noise radiation. Significantly, for each edge configuration, the spectra for different flow speeds, flap angles, and surface roughness were successfully scaled by utilizing aerodynamic performance and boundary-layer scaling methods developed herein.     

Investigation of airframe noise for a large-scale wing model with high-lift devices

The acoustic characteristics of a large-scale model of a wing with high-lift devices in the landing configuration have been studied in the DNW-NWB wind tunnel with an anechoic test section. For the first time in domestic practice, data on airframe noise at high Reynolds numbers (1.1–1.8 × 10⁶) have been obtained, which can be used for assessment of wing noise levels in aircraft certification tests. The scaling factor for recalculating the measurement results to natural conditions has been determined from the condition of collapsing the dimensionless noise spectra obtained at various flow velocities. The beamforming technique has been used to obtain localization of noise sources and provide their ranking with respect to intensity. For flap side-edge noise, which is an important noise component, a noise reduction method has been proposed. The efficiency of this method has been confirmed in DNW-NWB experiments.     

An experimental study of reducing narrowband noise of a slat using chevrons

A new concept of reducing the noise of a slat by applying a chevron form to the bottom edge is experimentally verified. The results of parametric studies are presented, which have been carried out on a small-scale model of a part of the wing (a scale of 1: 18) with deflected high-lift devices (the slat and the flap) in the landing configuration. As a result of acoustic measurements, a decrease (up to 4.5 dB) in narrowband noise for some chevron geometries is observed in comparison to a usual slat. The value of the decrease is a complex function of frequency, the wing and slat geometry, and the flow characteristics.     

基于物理机制模型的民机机体噪声预测

为实现民机总体方案快速评估与优化迭代设计,文章对民机增升装置前缘缝翼及后缘襟翼分别建立了基于民机噪声物理机制的预测模型,在此基础上搭建了机体噪声预测体系,开发了相应的预测工具UNICRAFT.为评估预测工具UNICRAFT的计算精度和效率,文章分别针对翼吊式布局,前缘缝翼/Fowler式襟翼形式,以及尾吊式布局,前缘缝...     

合成双射流对下游声压级影响试验

在Ma=0.4的来流条件下, 利用安装在主翼后缘处的合成双射流激励器对襟翼上的流动进行控制, 在风洞中开展了合成双射流对下游声压级影响的研究. 基于脉动压力测量结果, 结合油流显示试验, 得到了合成双射流对下游不同流动状态区域声压级影响的一些结论. 对于附着流, 在其峰值频率附近激励会明显提高其声压级; 对于受旋涡主导的流动, 恰当的合成双射流控制可以降低声压级, 激励频率较为关键. 在俯仰运动过程中, 对于附着流, 激励提高了声压级, 但不改变其迟滞特性; 对于受旋涡主导的流动, 激励对声压级的影响与攻角有关, 能够减弱其迟滞特性, 但激励强度对迟滞特性的影响较小, 减小声压级的最佳激励与运动历程有关.      

On the generation of side-edge flap noise

A theory is proposed for estimating the noise generated at the side edges of part span trailing edge flaps in terms of pressure fluctuations measured just in-board of the side edge on the upper surface of the flap. Asymptotic formulae are developed in the opposite extremes of Lorentz contracted acoustic wavelength large/small compared with the chord of the flap. Interpolation between these limiting results enables the field shape and its dependence on subsonic forward flight speed to be predicted over the whole frequency range. It is shown that the mean width of the side edge gap between the flap and the undeflected portion of the airfoil has a significant influence on the intensity of the radiated sound. The results indicate that the noise generated at a single side edge of a full scale part span flap can exceed that produced along the whole of the trailing edge of the flap by 3 dB or more.     

Flow field measurements of leading-edge separation vortex formed on a delta wing with vortex flaps

Wind tunnel tests are carried out using a 70 delta wing model with leading-edge vortex flaps. The structure of the leading-edge separation vortex over the leading-edge vortex flap is measured by use of a 5 holes pitot probe, surface pressure measurement technique and oil flow visualization technique. Separation vortices formed on a plain delta wing, on a vortex flap and inboard the vortex flap hinge line are clearly visualized. Results indicate that the flow around the vortex flaps is classified into several different cross flow patterns. The streamwise flap deflection angle is defined to discuss the vortex flap performance. The optimum lift to drag ratio is attained when the amount of the wing angle of attack is not far different from that of the streamwise flap deflection angle, as long as the vortex flap is deflected modestly.     

机翼后缘噪声预测研究

机翼后缘噪声是飞机重要的机体噪声源之一。本文基于CFD(Computational Fluid Dynamic)数值模拟和Ffcows Williams-Hall理论,研究应用了一种预测干净机翼后缘气动噪声的方法。采用Menter’s SSTκ-ω湍流模型对翼型和机翼进行N-S方程数值模拟得到后缘附近的湍流特征速度和特征长度,再利用Serhat Hosder的预估方法计算后缘噪声强度级。本文首先计算了NACA0012翼型在7种不同状态的后缘噪声,计算结果与实验值比较,符合很好,从而证明了本文采用的方法的可行性和正确性;然后研究了两个亚音速翼型(NACA 0009,NACA 0012),两个超临界翼型(SC(2)- 0710,SC(2)-0714),EET机翼的不同参数对后缘噪声强度级的影响,得出了对降低后缘噪声有参考意义的结论。     

襟翼侧缘噪声机理及修型降噪设计

襟翼侧缘噪声是飞机起降阶段机体噪声的重要噪声源。采用极大涡模拟对襟翼侧缘非定常流场进行数值模拟,分析其噪声产生机理.基于此,提出了两种襟翼侧缘修型方式,应用虚拟渗透面的Ffowcs Williams and Hawkings(FW-H)声比拟方法将修型构型的远场噪声频谱特性和指向性与基准构型对比分析,研究其降噪效果。通过流场和声场的数值模拟表明,襟翼侧缘噪声属于宽频噪声。不同的襟翼侧缘形状改变了流场形态、侧缘涡结构以及涡系的发展过程,进而对声源分布和远场噪声特性产生影响。结果表明:在给定的5°计算迎角下,两种襟翼侧缘修型方式在保证增升装置的原有升阻气动特性的前提下,能达到减小全场总声压级1~2 dB的降噪效果。     

Aerodynamic sound generation of flapping wing

The unsteady flow and acoustic characteristics of the flapping wing are numerically investigated for a two-dimensional model of Bombus terrestris bumblebee at hovering and forward flight conditions. The Reynolds number Re, based on the maximum translational velocity of the wing and the chord length, is 8800 and the Mach number M is 0.0485. The computational results show that the flapping wing sound is generated by two different sound generation mechanisms. A primary dipole tone is generated at wing beat frequency by the transverse motion of the wing, while other higher frequency dipole tones are produced via vortex edge scattering during a tangential motion. It is also found that the primary tone is directional because of the torsional angle in wing motion. These features are only distinct for hovering, while in forward flight condition, the wing-vortex interaction becomes more prominent due to the free stream effect. Thereby, the sound pressure level spectrum is more broadband at higher frequencies and the frequency compositions become similar in all directions.     

人头散射对虚拟声屏障的性能影响分析

在噪声来自于多个方向的普通房间中,通过立体结构的虚拟声屏障(Virtual Sound Barrier,VSB)系统能够产生比人头大的静区。实际应用中人头处于系统包围的静区内,必须考虑人头的散射作用对系统的影响。数值模拟表明,由于人头的散射作用,在人头附近,声压降低量分布更为均匀,系统性能可能变好也可能变坏,与误差传感器包围区域的半径及噪声频率有关。系统性能随系统物理配置的变化趋势,与未引入人头时是一致的。人头可以在系统包围的静区内移动,随着人头偏离系统中心,降噪效果会下降,但即使人头偏离至系统包围静区的边缘,仍有10 dB以上的降噪。实验给出一种实用的圆柱状分布的16通道的VSB系统,引入人头后系统性能变好了。当人头在该系统包围的静区内移动时,即使频率达到500 Hz,降噪效果最差仍达13.3 dB。     

锯齿尾缘降噪翼型优化设计研究

大量研究工作表明旋转风电叶片的主要气动噪声来自叶尖尾缘区域,一直以来都是严重影响居民生活和叶片气动性能发挥的重要因素之一.为此,针对决定叶片重要气动特性单元——二维翼型,采用有别于传统的仿猫头鹰翅膀锯齿尾缘流动控制方法,将锯齿关键尺寸参数融入到风力机翼型设计之中,从而开发仿生锯齿翼型的优化设计方法,获得低噪声与高气动性...     

无缝襟翼吹气控制机理和地面效应分析

基于Coanda效应的无缝襟翼吹气控制能大幅度提升机翼升力, 改善大型运输类飞机起降性能, 因此研究起降阶段地面效应对吹气控制的影响十分必要。通过数值模拟方法, 从流场变化的角度分析了无缝襟翼吹气控制机理, 以及有/无襟翼吹气时地面效应对翼型气动性能的影响。襟翼吹气使Coanda表面产生局部低压区, 形成指向Coanda表面的压力梯度, 进而引起射流上方的主流偏转和加速, 使整个翼面近壁区产生顺时针方向的速度增量; 翼面压力面的压力增大, 吸力面的吸力增强, 其中主翼上翼面吸力增强是翼型升力增加的主要来源。无吹气时, 地面效应使翼型上/下翼面附近的流速均降低, 上/下翼面的压力均有所提高, 整体上使翼型升力降低。有地面效应时的襟翼吹气增强了下翼面对来流的阻滞作用, 进一步提高了下翼面的压力; 襟翼吹气使上翼面气流加速, 可抵消地面效应引起的上翼面气流减速, 一定程度上减小了地面效应引起的上翼面吸力损失。      

Binaural coherence edge pitch

The binaural coherence edge pitch (BICEP) is a dichotic broadband noise pitch effect similar to the binaural edge pitch (BEP). The BICEP stimulus is made by summing spectrally dense sine wave components with random phases. The interaural phase angle is a constant (0 or pi) for components with frequencies below (or above) a chosen edge frequency, and it is a random variable for the remaining components. The chosen edge frequency is a coherence edge because the noises to the two ears are mutually coherent within any band of frequencies on one side of the edge and they are mutually incoherent in any band on the other side. Pitch-matching experiments show that the BICEP exists for coherence edge frequencies between about 300 and 1000 Hz. It is matched by a pure-tone frequency that differs from the edge frequency by 5% to 10%. The matching frequency lies on the incoherent side of the edge, an important result that is consistent with the way that the equalization-cancellation model has been applied to binaural pitch effects, especially the BEP. The results of BICEP experiments depend upon whether the coherent components are presented in 0 or pi interaural phase for some listeners but not for all. The BICEP persists if the noise to one of the ears is delayed, but it becomes weaker and less well matched as the delay increases beyond 2 ms. The BICEP does not depend on whether the component amplitudes are all created equal or are given a Rayleigh distribution. Some reliable pitch sensation exists even when the component amplitudes are entirely independent in the two ears, so long as the phase coherence conditions of the BICEP stimulus are maintained. The existence of the BICEP is a challenge for current models of dichotic pitch because none of them predicts all its features.     

Experimental investigation of coupling effects of passenger compartment and trunk of a car on coupled system natural frequencies using noise transfer function

The parcel shelf of a car has several holes for speakers and electrical devices. In addition, air ventilation holes are installed on the trim that covers the parcel shelf. The effect of the holes between the two cavities, passenger compartment and the trunk, and the natural frequencies of double cavities connected by the neck (parcel shelf) are very vital and useful to noise–vibration–harshness engineers, as the low frequency resonances contribute to the booming noise inside the car. In the present study, the coupling effect of the passenger compartment and the trunk connected through the holes on the parcel shelf in between, has been investigated experimentally using noise transfer function. The first and second coupled system modes are measured at around 40 Hz and 70–80 Hz respectively. By increasing the effective size of the holes on the parcel shelf, the first and second natural frequencies of coupled modes can be shifted to higher values. The current study has verified that holes act as point sources in the low frequency ranges. It was concluded that the coupled acoustic modes, in the low frequency range, are strongly controlled by fluid–structure interaction as well as changes in the panels mass and stiffness in the car interior space. The shift in the natural frequencies of connected cavities can be useful in the prediction of the interior noise in an automobile as well as provide a verification tool for conventional numerical techniques such as finite element methods.     

Investigation of structural response and noise reduction of an acoustical enclosure using SEA method

Noise reduction capability of acoustical enclosures has been extensively investigated and is commonly quantified by noise reduction. Although much work has been done in predicting the noise reduction by using statistical energy analysis (SEA) method, discrepancy often exists between the predicted and measured results, especially at the low and intermediate frequencies. This is largely due to the fact that some physical mechanisms which affect the prediction of noise reduction were not addressed in the available SEA models. In this paper, the sources of the discrepancy were identified by investigating the limitation of SEA for energy transfer in the entire frequency range and the effect of structural–structural coupling, acoustical–structural coupling on the prediction of noise reduction. An improved SEA model including the non-resonant response and more accurate transmission coefficient of finite panels is presented. Finally, the predicted structural response and noise reduction of an acoustical enclosure were compared with measured results, and the improved agreement between the prediction and experiment was observed.     

An experimental study of airfoil instability tonal noise with trailing edge serrations

This paper presents an experimental study of the effect of trailing edge serrations on airfoil instability noise. Detailed aeroacoustic measurements are presented of the noise radiated by an NACA-0012 airfoil with trailing edge serrations in a low to moderate speed flow under acoustical free field conditions. The existence of a separated boundary layer near the trailing edge of the airfoil at an angle of attack of 4.2 degree has been experimentally identified by a surface mounted hot-film arrays technique. Hot-wire results have shown that the saw-tooth surface can trigger a bypass transition and prevent the boundary layer from becoming separated. Without the separated boundary layer to act as an amplifier for the incoming Tollmien–Schlichting waves, the intensity and spectral characteristic of the radiated tonal noise can be affected depending upon the serration geometry. Particle Imaging Velocimetry (PIV) measurements of the airfoil wakes for a straight and serrated trailing edge are also reported in this paper. These measurements show that localized normal-component velocity fluctuations that are present in a small region of the wake from the laminar airfoil become weakened once serrations are introduced. Owing to the above unique characteristics of the serrated trailing edges, we are able to further investigate the mechanisms of airfoil instability tonal noise with special emphasis on the assessment of the wake and non-wake based aeroacoustic feedback models. It has been shown that the instability tonal noise generated at an angle of attack below approximately one degree could involve several complex mechanisms. On the other hand, the non-wake based aeroacoustic feedback mechanism alone is sufficient to predict all discrete tone frequencies accurately when the airfoil is at a moderate angle of attack.     

Sound radiation from real airfoils in turbulence

Leading edge noise measurements and calculations have been made on a three airfoils immersed in turbulence. The airfoils included variations in chord, thickness and camber and the measurements encompass integral scale to chord ratios from 9 to 40 percent as well as 4:1 ratios of leading edge radius and airfoil thickness to integral scale. Angle of attack is found to have a strong effect on the airfoil response function but for the most part only a small effect on leading edge noise because of the averaging effect of the isotropic turbulence spectrum. Angle of attack effects can therefore be significant in non-isotropic turbulence and dependent on airfoil shape. It is found that thicker airfoils generate significantly less noise at high frequencies but that this effect is not determined solely by the leading edge radius or overall thickness. Camber effects appear likely to be small. Angle of attack effects on the response function of a strongly cambered airfoil are shown to be centered on zero angle of attack, rather than the zero lift angle of attack.     

基于正交设计的风力机翼型尾缘襟翼参数分析

引入试验中正交设计的思想,通过数值模拟研究了风力机翼型尾缘襟翼不同参数的影响。采用带有转捩模型的SST k-ω湍流模型模拟了基于S809的尾缘襟翼的尺寸、偏斜角度和形状的影响。结果表明:尾缘襟翼尺寸、偏斜角度对于翼型相关气动参数影响较大,在考查参数范围内折中采用10%弦长、偏斜10°的尾缘襟翼综合性能较好;尾缘襟翼形状函数影响相对较小,采用变化较平缓的尾缘襟翼有利于保持流动稳定性。     

Improvement of noise reduction performance for a high-speed elevator using modified active noise control

A high rise building demands a high-speed elevator. Since a high-speed elevator has various transfer paths of noise transmitted from motor and rope to cabin interior, it is very difficult to solve the noise problem. Most research for noise reduction has been performed regarding passive noise control by using mainly absorption material and insulation material. In this study, while it is modeling as multiple-input and single-output with respect to transfer paths of high-speed elevator on conditions of stationary and driving states, the characterized frequency in the cabin is discovered through a contribution technique. It is able to replace by 1-dimensional model to control noise at a major contributed frequency. Also, a new active noise control technique has been proposed to control the cabin noise effectively at unpleasant area that is required to make quite zone for passenger. The Correlation Filtered X-LMS (Co-FXLMS) algorithm has been applied to control the dominant frequency noise that it has a high contribution. Simultaneously, this study has a proposed Moving Band Pass Filter (MBPF) to improve the performance of active noise control in the cabin which is able to apply a dynamic system with time variant states. Finally, we obtained the 8 dB noise reduction in the cabin at ear level and it has been proved that the modified active noise control using Co-FXLMS algorithm and MBPF is available to improve the performance of noise reduction.