上游转子对下游静子叶片气动力的影响

为了研究轴流压气机上游转子对下游静子干扰产生的叶片非定常气动力的大小和频率的变化规律,采用在静子叶片表面埋设微型动态压力传感器的方法,在一台低速单级轴流压气机实验器上进行了静子叶片表面压力的测量。测量覆盖了不同轴向间距、不同转速下从近堵塞到近失速的宽广范围,并对实验测量得到的静子叶片非定常气动力进行离散傅里叶变换,以分析其频谱特性。通过对实验结果的分析,初步认识了流量、轴向间距及转速等因素对轴流压气机转/静干扰影响的规律。     

共轴双旋翼非定常流场干扰特性

直升机共轴双旋翼相遇过程的非定常气动干扰在其周期性干扰中最为强烈。为了研究该过程中的干扰特征,建立了一个基于非定常雷诺平均Navier-Stokes方程的气动干扰数值方法,双旋翼的反转运动采用运动嵌套网格进行模拟。为了探究双旋翼相遇时的气动干扰机理,以两个相对运动的双翼型系统来模拟双旋翼特定展向截面的非定常相遇过程。分析了双旋翼和双翼型相遇时的气动特性和流场特征,并对双翼型系统进行了参数影响研究,结果表明:双旋翼上下桨叶相遇时,上下旋翼拉力均会出现先增后减的变化趋势且波动幅值分别为其对应总拉力的30%和22%,双翼型系统的升力波动趋势与之相似;间距增大使上下翼型间的气动干扰减小,且上下翼型升力波动对间距变化的敏感时间不同;翼型相对厚度增大使双翼型升力波动幅值增大,并出现二次波动;有附加来流时,相对来流速度较小的翼型升力波动的幅值与范围更大。      

Experimental study of rotor blades vibration and noise in multistage high pressure compressor and their relevance

Rotor blades fault of aeroengine compressor is mostly caused by mechanical and aerodynamic excitation. And the excitation factor of high intensity sound wave to rotor blades should not be ignored. Experimental researches are conducted on a multistage high pressure compressor. When high level vibration occurs on the first stage of rotor blades, the noise spectrum presents typical characteristic for discrete multi-tone in the compressor. The amplitude of blade vibration displacement and the sound pressure level of characteristic frequency noise increases and decreases simultaneously and reaches the maximum value at the same time. This frequency merely occur on a certain speed range and is locked in a specific range which presents no variation with the rotating speed. When high level vibration occurs on the first stage of rotor blades, the noise spectrum presents a sharp peak and the propagation state of the characteristic frequency is a helix structure in the compressor. It can be confirmed that acoustic resonance occurs in the multistage compressor. The acoustic resonance frequency and its side band frequencies are generated by modulation of a rotating noise source at the rotor speed which is the excitation source of the rotor blades vibration.     

在尾流激振情况下叶片振动应力预估技术

研究了前排静子叶片的尾流对后排转子叶片振动的影响.采用参数多项式方法和振荡流体力学理论, 求解静子叶片后的尾流场及尾流场作用下转子叶片通道内的非定常流场.把非定常气动分析给出的压力场, 转化为结构动力分析中的载荷压力场形式.根据试验结果得出响应分析中的阻尼, 先求解出各阶谐波作用下转子叶片的响应结果, 再把各阶响应结果进行叠加, 得到总响应.从流场求解到响应求解, 为工程应用初步建立起了一个尾流激振情况下叶片振动应力预估的半经验方法.      

上游叶片尾迹对转子叶片非定常表面压力频谱特性影响的研究

为了研究上游叶片尾迹对轴流压气机转子叶片非定常表面压力的影响,采用在叶片表面埋设微型压力传感器的方法,测量了一个单级低速轴流压气机转子叶片的非定常压力分布。对转子叶片非定常压力分布的分析显示:转子叶片压力面非定常表面压力主要受上游叶片尾迹影响,其主导频率为上游叶片尾迹频率及其倍频,压力波动幅度随上游叶片尾迹的衰减而沿流向减弱。转子叶片吸力面非定常压力受叶片附面层和上游叶片尾迹共同影响,其主导频率为上游叶片尾迹频率及其倍频,但是在吸力面前部气流加速区压力波动幅度沿流向增大,而在吸力面后部气流减速区压力波动幅度沿流向减小。在存在尾缘分离的情况下,在分离区附近产生较大压力波动。尾缘气流分离产生的压力波动频谱中含有上游叶片尾迹频率及其倍频的分量,但其频谱可能比较复杂,并非单一地受上游叶片尾迹影响。      

Characterization of component interactions in two-stage axial turbine

This study concerns the characterization of both the steady and unsteady flows and the analysis of stator/rotor interactions of a two-stage axial turbine. The predicted aerodynamic performances show noticeable differences when simulating the turbine stages simultaneously or separately. By considering the multi-blade per row and the scaling technique, the Computational fluid dynamics(CFD) produced better results concerning the effect of pitchwise positions between vanes and blades. The recorded pressure fluctuations exhibit a high unsteadiness characterized by a space–time periodicity described by a double Fourier decomposition. The Fast Fourier Transform FFT analysis of the static pressure fluctuations recorded at different interfaces reveals the existence of principal harmonics and their multiples, and each lobed structure of pressure wave corresponds to the number of vane/blade count. The potential effect is seen to propagate both upstream and downstream of each blade row and becomes accentuated at low mass flow rates. Between vanes and blades, the potential effect is seen to dominate the quasi totality of blade span, while downstream the blades this effect seems to dominate from hub to mid span. Near the shroud the prevailing effect is rather linked to the blade tip flow structure.     

Null phase-shift polarization filtering for high-frequency radar

In order to effectively cancel the interference in polarization filtering, the parameters of the polarization filter should timely adapt to the variation of the polarization of the interference, which may impact the amplitude and phase of the desired signal that passes through the same polarization filter during the coherent integration time (CIT) and render the enhancement of the signal integration a failure. To avoid this, a null phase-shift polarization (NPSP) filter is proposed, which is composed of a linear polarization transformer (LPVT), a conventional single-notch polarization (SNP) filter and an amplitude/phase compensation device (A/PCD). The interference, which has polarization different from those of the desired target signal, can be suppressed completely while the target signal remains without distortion. Some applications of high-frequency (HF) radars for suppressing the radio interference are introduced. Simulation results from the experimentally derived data indicate that the improvement of the signal-to-interference ratio (SIR) can be expected to be more than 28 dB. The proposed NPSP filter is effective in HF radar or other coherent systems.     

Interference Effects of Pseudo-Random Frequency-Hopping Signals

When a pseudo-random frequency-hopping signal is intercepted by a conventional receiver operating within the same frequency band, the interfering signal has the form of a pulse-amplitude modulated signal. Each pulse amplitude is dependent upon the hopping frequency and the selectivity characteristic of the victim receiver. The probability density function for the interfering pulse amplitude prior to demodulation is determined when the probability density function for the hopping frequency is uniform and the victim-receiver characteristic is 1) ideal flat bandpass, 2) single tuned, and 3) Gaussian shaped. It is shown that the average interfering pulse amplitude and interference power decrease as the frequency-hopping bandwidth increases with respect to the victim-receiver bandwidth. Fast Fourier transform computer techniques are used to obtain the probability density function of the interference amplitude in a Gaussian receiver when several (from 2 to 10) pseudo-random frequency-hopping systems are simultaneously using the same frequency band. The probability that the interference exceeds a prescribed threshold value is computed from the derived probability density functions. This probability may be used in signal-to-interference ratio calculations, to describe the capture effect, or to compute the expected number of clicks produced in an FM discriminator.     

非定常流场分析结果向结构载荷压力场转化问题的解决

在研究前排静子叶片尾流对后排转子叶片振动的影响时．一个很大的难题就是如何将尾流场作用下的转子叶片通道内的非定常流场转化为适于振动响应分析的结构载荷压力场的形式，并引入有限元分析。在本文中，首先将转子叶片通道进口处的尾流参数进行傅立叶分解，然后分别对各阶谐波作用下的转子叶片通道内的非定常流场进行计算，将其叠加，得到整个非定场流场的解。这样，在进行振动谐响应分析时，各阶谐波作用下的载荷压力场实际上就是其对应的各阶非定常压力场。同时，通过一定的简化，把非定常气动分析结果转化为适于ANSYS谐响应分析的加载形式，从而成功地把结构载荷压力场引入了有限元分析。     

多级轴流压气机噪声源特性分析

某型轴流式压气机高压一级转子叶片出现大幅振动,并且振动频率不是转频的整阶次,即叶片非同步振动。对叶片的激励可能来源于气动和非定常流场,就包含了声场。为了研究叶片出现非同步振动时的压气机声场,在压气机机匣内壁上对压气机噪声进行测量。通过分析得知,噪声信号特征频率的出现与叶片非同步振动同时出现,主要影响因素有压气机转速、结构调节状态等参数。     

转子叶栅非同步振荡发声特性研究

轴流压气机转子叶片排振荡疲劳失效是常见的气动弹性失稳问题。当转子叶栅处于非同步振荡状态下时,压气机管道内部将伴随着异常噪声的产生,这类噪声的频率既不是分布在叶片通过频率及其谐波上,也不是分布在转子轴频率及其谐波上,同时也不满足简单多普勒效应。为了解释这种异常噪声现象,以三维升力面理论为基础,讨论叶片对其附近流体施加非定常载荷的发声问题,给出了转子叶栅振荡异常发声问题的物理解释,建立了声场频率及模态特性与转子声源特性的直接关系式,并给出了频率特性不同于叶片通过频率且不符合简单多普勒效应的完整解释。在此基础上,通过机理性实验研究证实了该模型的正确性。实验结果表明,理论预测声场的频率和周向模态特性与实验结果完全一致。     

耦合进排气壳的增压器涡轮流动干扰及激振力弱化研究

为探究船用增压器涡轮在耦合进排气壳条件下的流动特性,采用SST湍流模型和FFT方法对某增压器轴流涡轮与进排气壳耦合的流场进行非定常数值模拟,重点分析排气壳非对称流场对涡轮动叶片压力的干扰特性和扰动来源,在此基础上提出基于导叶非对称布局的激振力弱化改型方案并进行了验证。结果表明：进气壳影响静叶前缘静压沿周向的分布,排气壳流场导致的非对称背压会给动叶表面造成低频的压力波动,约为3.6%的转子通过频率,在尾缘吸力面处该低频波动幅值大于动静叶排干涉导致的高频波动幅值;排气壳内部复杂的分离流动和涡系结构是产生上述流动干扰的主要原因。4种非对称布局方案都能在几乎不影响涡轮性能的前提下分散并弱化高频波动幅值;其中Case2尾缘高频幅值减小了98.6%,低频幅值减小了52.6%,而且涡轮效率还有略微提高,为最优布局。     

基于apFFT的罗兰-C窄带干扰频域抑制方法

针对现有罗兰-C接收机普遍采用固定陷波电路抑制窄带干扰的情况,提出了基于全相位谱分析(apFFT)的频域精确自适应陷波罗兰-C窄带干扰抑制方法,设计了基于双相移组合全相位法的FIR频域陷波器。在对窄带干扰进行精确谱分析的基础上,设计相应频点的陷波器对多个窄带干扰进行抑制。基于MATLAB的仿真结果表明:该方法能够根据罗兰-C窄带干扰频率的变化,实现频点任意控制的频域自适应陷波,有效恢复出罗兰-C信号,为增强型罗兰-C接收机的设计提供了一种简单有效的窄带干扰抑制方法。     

Signal Interference and Improvement of Signal-to-Noise Ratios in a Half-Wave Linear Detector

Signal interference in the half-wave linear detector has been studied only for amplitude modulation. In this paper, we treat signal interference for both an amplitude-and an angle-modulation communication system. The input to the half-wave linear detector is assumed to be composed of an amplitude-modulated wave, an angle-modulated wave, and narrow-band Gaussian noise. In particular, when strongweak relations exist in the input processes, a detailed analysis for the output component is presented to clarify some useful output properties.     

Omnidirectional Instantaneous Direction Finding System

A system for providing near-instantaneous determination of the azimuthal angle of arrival of a received signal has been designed and fabricated at L band. Direction is determined by phase measurement of the outputs of a multimode antenna, which has no moving parts. Effects of multipath interference are reduced to a minimum through a combination of signal processing techniques. The position of the transmitting source is presented on a PPI display.     

压气机内部噪声特征与转子叶片声固耦合机理分析

航空发动机压气机转子叶片故障多由机械激励和气动激励造成，而高强声波对转子叶片的激振因素不容忽视。通过开展某型涡扇发动机压气机内部噪声测试试验，研究压气机转子叶片振动机理及其与噪声信号的对应关系。阐述了压气机内部旋转不稳定性非定常压力波作用机制，提出了基于刚性壁声波导管技术的导出式噪声测量方法，完成了某型涡扇发动机压气机内部噪声信号测试，对噪声信号进行了频谱分析和声传播特性分析。研究结果表明，某型涡扇发动机压气机内部噪声信号频谱呈现高峰值纯音分量1 402 Hz，并且该纯音分量与转子叶片通过频率呈现特定的频率组合关系。该纯音分量的噪声源在压气机内部沿发动机顺航向方向从后向前传播。利用旋转不稳定性理论，将声源频率在不同坐标系下进行转换，当噪声源周向模态数为13时，该纯音分量可调制出与高压一级转子叶片一阶振动频率相对应的激振频率。     

后置静叶周向弯曲对表面非定常压力脉动的影响

在目前的叶轮机械中,普遍存在着旋转动叶与后置静叶干涉产生的非定常流动现象。这种流动现象会导致静叶表面产生非定常性压力脉动。这种脉动可分为旋转动叶的速度亏损尾迹引起的叶片表面的周期性脉动和气流本身的湍流脉动及其他涡团导致的随机脉动两个方面。采用一工业用单级通风机,对其动静叶的干涉现象进行研究。通过在后置静叶表面沿弦长及叶高方向布置动态压力传感器的方法,研究静叶的周向弯曲（倾斜）角度对静叶表面的非定常力的影响。研究结果表明：采用周向弯曲静叶会改变动叶尾迹所引起的后置静叶周期性脉动的幅值在静叶表面的分布特点,静叶顶部压力脉动的幅值与原始径向静叶相比能够有效地降低,同时与中部的压力幅值相比有一定提高,但整体呈现下降趋势;另一方面,静叶表面随机性的压力脉动强度受周向弯曲的影响较小。     

不对称静子叶片非谐方案研究

为降低转子叶片在前排静子尾迹流场激振情况下的动应力,对转子系统进行不对称气动非谐设计.不对称静子叶片分布非谐设计下,转子所受到的激振力由静子叶片均布情况下的单频率高幅值激振力转变为多频率成分低幅值激振力.对不对称静子叶片非谐情况下激振力频率幅值进行推导,讨论了静子扇区分布和静叶数目选取对尾流激振力的影响,并对相同扇区分布不同静叶数目情况下转子叶片的强迫响应进行瞬态分析,给出不对称静子非谐设计的最优方案.      

基于FFT的航空发动机整机振动分量实时跟踪监视

依据DFF(离散傅立叶变换),FFT(快速傅立叶变换)、加窗等数字信号处理理论,以及复指数函数的相关性质,并结合目前国内航空发动机整机振动信号处理现状,提出了基于FFr的航空发动机整机振动分量跟踪监视方法.该方法首先将时域加速度振动信号分解为多个简谐振动合成结果,然后根据系统输人的转子转速信号,跟踪计算转子基频激起的简...     

转静干涉下转子叶片的非定常压力频谱

分别采用多通道模型和相位延迟方法的单通道模型对一压气机转子叶片因转静干涉引起的表面非定常压力进行了分析.对比了转子叶片表面非定常压力的时域和频域信息,并对其高阶主导频率进行了分析.结果表明:相位延迟方法与多通道法计算结果吻合,转子叶片非定常压力的峰值频率为叶片通过频率及其倍频,叶片中部以上区域2倍叶片通过频率的非定常压力幅值约为1倍频的2倍,分析认为这是由尾迹输运和激波振荡导致的,可为深入分析叶片由振动导致高循环疲劳失效的成因提供参考.