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.