气动声学相似理论与试验研究

本文研究了气动声学的一般性相似原理,为气动声学的模型实验研究方法建立理论基础。由此得到了四个关于气动声场相似的相似准则数,导出了适合于流动分析的相似条件。对非定常流动中所产生的脉动力谱进行的相似分析,证实当气动力学完全相似时,以Strouhal数作为无量纲频率参数的脉动力谱函数也完全相似,此时,在几何相似点上测得的声谱在以St数作为频率坐标的频谱图上完全相同。风扇噪声的试验证实了气动声学的相似律。 

AEROACOUSTIC SIMILARITY PRINCIPLES AND THEIR EXPERIMENTAL INVESTIGATON

The general similarity principles in aeroacoustics are studied so as to provide the theoretical basis for aeroacoustic model experimental investigation of jet engine, fan, compressor, propeller etc. The analysis of the characteristics of fundamental aerodynamic noise sources shows that any aeroacoustic phenomenon is a similitude structure phenomenon. The most important result of the study is the establishment of four similarity criteria of aeroacoustic field which are expressed in a suitable form for flow analysis. For the fundamental aerodynamic noise sources,the similarity criteria are the Mach number of the flow,the Strou-hal number of the fluctuating frequency of the aerodynamic noise sources, and the nondi-mensional source strength (q or F or 6)relating to the type of the source, respectively.The main aerodynamic noise sources in turbomachinery are the fluctuating forces of fluid flow acting on the solid surfaces. The analysis of fluctuating force spectra in the un steady flows both of the model and the prototype indicates that the fluctuating force spectra both of them expressed in Strouhal number are also similar provided their flows are entirely similar. In this case, the overall sound pressure levels and the noise spectra measured at geometrically similar points are completely identical when the noise spetra are represented in Strouhal number. The results of the further research on the effect of Reynolds number show that it is unnecessary to maintain the Reynolds number similarity rule if the Reynolds numbers in full-scale fan and model-scale fan are both greater than 4xl05, But in the model test for the purpose of aerodynamic noise research,the strict identity of the blade tip Mach numbers between the model fan and the prototype fan should be ensured even if the flow Mach numbers are very small.The aeroacoustic similarity principles are demonstrated by the experiments for similarity of noise characteristics between the full-scale and model-scale fans.