Abstract: The air experiment results of three nitrogen cycle compressors with high speed and low flow rate showed obvious differences in performance. By comparing the structural parameters, it's found that there existed a big difference in the front clearance size of the impellers. The size has a significant influence on the performance of compressors. In order to study the influence of clearance on performance, numerical simulation of the three-dimensional flow field CFD method has been adopted for the over current fluid part of the compressor. The results indicate that the pressure ratio increased obviously when the clearance value was smaller, and the reason for the changed pressure ratio was that the reduction of clearance value would influence the distribution of static pressure coefficient inside the impeller; when the clearance value was small, the tip clearance flow had less interference on the flow field inside the blade, and the efficiency of the whole machine would also be improved. Different clearance values resulted in different tip clearance flow which would change the surface load distribution of different blade heights. The above research results are of great significance to improve the structure and performance of the fans in the later period.

Key words: circulating fan, blade front clearance, numerical simulation