简化起落架噪声相似准则及马赫数比例律

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。

Similarity rule and Mach number scaling law for simplified landing gear noise

Noise generated from real aircraft component can be researched through aeroacoustic experiment of scaled model,but some suitable similarity rules must be followed.The frequency similarity rule usually follows Helmholtz number scaling or Strouhal number scaling,and the source strength similarity rule is normally chosen as Mach number similarity in a certain range of Reynolds number.The scaling law of noise magnitude according to the freestream Mach number is useful for applying wind tunnel noise data to real flight condition and estimating the type of noise source.An aeroacoustic experiment of a 1/2 scaled simplified landing gear model of landing gear noise database for civil aviation authority validation (LAGOON) project is carried out in D5 aeroacoustic wind tunnel at Beihang University.Experimental results indicate that the frequency similarity rule of this landing gear model satisfies the Helmholtz number similarity but not the Strouhal number similarity law.The scaling law of landing gear noise according to the freestream Mach number is highly dependent on the frequency.At low frequency range,the noise spectrum satisfies the sixth power scaling law,while at high frequency range the noise spectrum satisfies the seventh power scaling law.A comparison of the transformed noise spectrum of D5 wind tunnel to that of the LAGOON project with the Helmholtz number similarity rule and the corresponding Mach number scaling law shows that thetwo results agree well with each other.