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真实飞机部件的气动噪声问题可以通过缩比模型气动声学试验研究,但是必须要遵循合适的相似准则。频率相似准则一般选择Helmholtz数或Strouhal数相似,而声源强度的相似准则在一定的雷诺数范围内通常采用Mach数相似。噪声随来流马赫数的比例律可用于外推风洞试验测量数据到真实飞行条件下,并判断声源类型。在北京航空航天大学D5气动声学风洞中对1/2缩比的LAnding Gear nOise database for civil aviation authority validatiON(LAGOON)简化起落架模型进行了气动声学试验研究。试验结果表明:该起落架模型的噪声频率遵循Helmholtz数相似准则而非Strouhal数相似准则。起落架噪声的马赫数比例律与频率有关,在低频范围内满足6次方关系,而在中高频范围内满足7次方关系。将D5风洞测得的噪声频谱按Helmholtz数相似及相应的马赫数比例律转换后与LAGOON原型试验结果对比,发现两者的测量结果吻合得非常好。
Aeroacoustic problems with real aircraft components can be studied by the acousto-acoustical experiments of a reduction ratio model, but the appropriate similarity criteria must be followed. The frequency similarity criterion is generally similar to the Helmholtz number or the Strouhal number, while the similarity criterion of the sound source intensity is usually similar to the Mach number within a certain Reynolds number range. The proportional law of noise with the flow Mach number can be used to extrapolate wind tunnel test measurements to real-world flight conditions and determine the type of sound source. The aerodynamic acoustics experiment of the LAnding Gear nOise database for civil aviation authority validatiON (LAGOON) simplified landing gear model was carried out in the aerodynamics wind tunnel of Beijing University of Aeronautics and Astronautics (D5). The experimental results show that the noise frequency of the landing gear model follows the Helmholtz number similarity criterion rather than the Strouhal number similarity criterion. The law of the Mach number of landing gear noise is frequency dependent, satisfying the 6th power relationship in the low frequency range and satisfying the 7th power relationship in the medium and high frequency range. Comparing the noise spectrum measured by D5 wind tunnel with the Helmholtz number and corresponding Mach ratio, the results are in good agreement with the LAGOON prototype test results.