The effect of diffuser on compressor performance and noise emission is studied in this paper. Firstly, on the basis of the mature compressor model, the airflow geometry from impeller inlet to volute exit has been simulated numerically. Then, the number of diffuser blade is changed and the impeller blade number remains unchanged. The effects of different diffuser blade number on compressor performance at three different compressor operating lines were analyzed and noise emission has been investigated at selected compressor operating point. It is found that flow range narrows down with blade number increase but there are pressure and efficiency enhancement at maximum efficiency working range with specific blade number. The noise simulation results show that there has the best stator blade number when the impeller blade unchanged. Moreover, a special kind of technique that called pinched diffuser is investigated in this paper. The results of four different pinch constructions indicate that the pinched diffuser can shift the surge line to low flow rates but the pressure passing through centrifugal compressor has decreased at the same time, small pinch is conducive to noise reduction which means there is also an optional structure that can obtain minimum noise, which means a more reasonable pinched construction design should be studied to improve the compressor performance and control the radiated noise.

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