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为研究超声速射流冲击斜板的噪声特性及声源特性,针对不同压比下,超声速射流流场及声场分别进行了高频PIV(particle image velocimetry)测量与远场噪声测量。PIV测量结果可观测到激波格栅形成过程以及冲击斜板对它的影响。声场测量结果可捕捉到自由射流与冲击射流中不同的纯音频率随压比增加的转变过程。通过一一对比各纯音模态与流场模态,可区分各纯音模态的声源特性。结果表明:当压比在2.0~3.2之间时,共出现五种纯音模态:A模态纯音频率为剪切层大尺度涡脱落频率,此时流场呈现同轴模态;d模态和e模态中纯音频率主要为冲击纯音频率,且e模态出现时流场转化为螺旋模态,这是一种不稳定模态;当压比大于等于2.53时,纯音模态稳定成单一模态B,B模态纯音频率为啸叫频率,其流场结构转化回同轴模态,啸叫频率对斜板的存在与否不敏感;啸叫频率随着压比的增加逐渐减小,其二次谐频在基频幅值较小的方向上会出现一个强声波辐射。 相似文献
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QIAO Wei-yang 《中国航空学报》2000,13(3):146-151
After the significant progress that has beenachieved in engine noise reduction in the last twodecades,the airframe noise of civil transportshas now become a major concern for noise certi-fication and environmental considerations.Con-sequently,aircraft manufacturers and researchcenters have been working on airframe noisewith the objectives of developing reliable noiseprediction schemes and reducing aerodynamicnoise generation at the source in recentyears[1~ 2 ] . Of all the airframe noise … 相似文献
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For a single omnidirectional sensor in contact with a constant velocity source that radiates a constant frequency tone, the measurements of the Doppler-shifted frequencies over time do not provide sufficient information to localize the source. Instead, only the parameters of source rest frequency, speed, and range relative to a sensor can be determined. However, if over time three or more sensors sequentially come in contact with the source, the source trajectory can then be specified. This is termed sequential localization. A two-dimensional grid search technique to find the Doppler parameters from measurements taken by a single sensor alone is presented. From these parameters, it is next shown how sequential localization is accomplished. Two simulation examples are provided to verify the development. The localization root mean squared errors (RMSEs) are found to be very close to the Cramer-Rao bound 相似文献
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压气机内部噪声特征与转子叶片声固耦合机理分析 总被引:1,自引:1,他引:0
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。 相似文献
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翁玉莲 《西安航空技术高等专科学校学报》2011,29(4):92-94
语气和语调之间存在相应的关系,以此为研究基础,寻找新闻评论和新闻消息两种不同的新闻语体在标号使用上所体现的语气差异,意图在语调的功能取向上确立消息和评论语体区别性的形式标记。 相似文献
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针对工程实现中主字母体制安控系统的指令实时检测性能受采样方案影响较大的问题,通过对单音信号频率、检测采样频率和采样点数的合理选择,提出了一种指令检测的采样优化实现方案。仿真实验结果表明,通过对采样方案的优化,在固定多普勒频偏和可变多普勒频偏情况下,可以最低采样点数实现指令可靠检测,便于利用FPGA实现实时处理。 相似文献
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《IEEE transactions on aerospace and electronic systems》2008,44(1):217-226
AC-DC converters with active power factor correction (PFC) are replacing uncontrolled diode rectification circuits on commercial jet airplanes in order to meet harmonic distortion limits imposed by new airborne electrical system power quality standards. The high line frequency of airborne AC power systems presents a major challenge for the design of PFC converters capable of meeting these standards. This paper investigates a new source of harmonic current distortion and the resulting system power quality problems related to dynamic interactions between PFC converters and the AC source. Experimental results are first presented to demonstrate the existence of such interactions and their effects on system power quality. Analytical and numerical simulation results are then presented to explain why such dynamic interactions can lead to significantly increased harmonic current distortion in steady state operation. Elimination of undesirable system interactions through proper damping of the PFC converter input filter is also presented and its effectiveness experimentally validated. 相似文献
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基于简化射线模型的剪切层相位修正方法 总被引:1,自引:1,他引:1
给出了基于简化射线模型的三维有限厚度风洞剪切层相位修正方法,利用数值模拟结果对该方法的物理依据进行了解释,并将其与传统的Amiet方法和平均马赫数法进行了对比研究,通过风洞试验对简化射线法的有效性进行了验证,最后给出了简化射线法对空间弯曲的剪切层的相位修正方法。结果表明:在来流马赫数小于等于0.3、测量角在40°~140°的范围内,当声源和传声器在同一个平面内时,对于风洞剪切层引起声波相位畸变修正,简化射线法、平均马赫数法和Amiet方法之间没有明显的差别,三种方法之间的相对误差小于1%。 相似文献
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三轴转台误差源对陀螺加速度表测试的影响 总被引:3,自引:0,他引:3
分析了三轴转台设备误差源;讨论了转台误差对陀螺加速度表测试精度的影响。根据陀螺加速度表的输入输出模型,建立了转台误差对陀螺加速度表系数辨识影响的数学表达式。 相似文献
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权海顺 《沈阳航空工业学院学报》2011,28(6):65-68
在日语声调研究领域中,从屈折形态学的角度揭示日语动词谓语的声调变化规律,是一个崭新的声调研究视角。基于此,通过屈折形态学的研究方法,主要探讨了日语动词谓语发生形态变化时所引发的声调核移位现象以及其主要特征。日语动词谓语发生屈折形态变化时,随着语素的增加,声调核的位置也发生复杂的变化。如果从屈折形态学的视角分析日语动词谓语的声调变化,就能进一步挖掘声调变化的内在规律。 相似文献
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An input filter is frequently employed between a switching regulator and its power source. However, its presence often results in degradation of dynamic performances and stability. The detrimental interaction is between an input filter and a switching regulator and is a function of the input filter parameters and also of the supply voltage. An earlier paper presented an analysis and design procedure aimed at developing a feed-forward loop to cancel this undesirable interaction. The feed-forward design is extended here to encompass a scheme that automatically accounts for changes in the supply voltage; the result is an adaptive compensation that tracks the input voltage variations. Experimental results are presented that confirm the adaptive nature of the design. 相似文献
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发动机进气道是飞行器的一个强散射源。本文采用射线跟踪法研究了任意截面形状,不同管道的电磁散射特性。用这种方法计算了一个角反射器雷达截面和一个实际使用的进气道的雷达散射截面,测量结果和计算结果的一致性表明,该方法是有效的。 相似文献
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基于射流噪声模拟试验台,对出口面积相同的圆形喷口及宽高比分别为1、1.5、2、10的矩形喷口亚声速射流的远场噪声辐射特性和噪声源分布位置进行了较为系统的研究。通过远场噪声测量,获得了不同宽高比矩形喷口在不同方位角平面的射流噪声频谱分布结果相对于圆形射流的差异,揭示了矩形射流潜在的降噪潜力。通过基于波束成形算法的传声器阵列,得到了矩形射流噪声源峰值位置随频率的变化情况,系统分析了射流速度、方位角、宽高比等参数对矩形射流噪声源分布的影响。射流速度和方位角对矩形射流噪声源分布的归一化结果影响很小,而宽高比对矩形射流噪声源分布有较大影响:随着矩形宽高比的增加,矩形射流低频段噪声源向上游偏移,高频段噪声源向下游偏移。 相似文献
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Anpredictionsystemforthein-ductsoundfieldinaeroenginecanprovidethetheoreticalfoundationforthepracticalengineeringsup-pressing... 相似文献
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