A Study of Similarity Problems Concerning the Working Media Helium and Air in an Axial-flow Compressor

With the axial speed of a helium axial compressor being less than or equals to 200 m/s,under the condition of identical geometric dimensions being guaranteed and with the first stage in the HP section serving as a simulator,the parameters of the stage can be given as follows:helium flow rate 4.72 kg/s,inlet pressure 1.0253×106 Pa and inlet temperature 35.5 ℃.When air instead of the helium was used to simulate the first stage of HP section in the helium compressor,research was performed on a variety of problems,such as the movement and kinetic incomplete similarity caused by the difference of the two working media helium and air in such physical parameters as density,viscosity and adiabatic index.In addition,a contrast analysis was also conducted of the establishment of similarity criteria by adopting respectively a definite physical quantity method and a differential equation approach,comparing the difference between the working media helium and air as well as its influence on the choice of similarity criteria.Pertinent reasons for the onset of deviations were analyzed and the similarity criteria for simulating a helium compressor with the use of air were identified as Sr,Re and Eu.The air simulation parameters corresponding to the design operating condition of the helium compressor were calculated.A contrast analysis of CFD (computational fluid dynamics) calculation results show that the simulation effectiveness is satisfactory.The foregoing research can provide a theoretical basis for conducting helium compressor tests.