The effects of pre-whirl flow generated by variable guide vanes (VIGVs) on the performance of a small centrifugal compressor has been investigated by experiments and three-dimensional CFD. The compressor efficiency and surge limit were examined experimentally. Axial-type VIGVs were employed in this study. The VIGV setting angles were 0, 12, 24, 36, 48 and 60degrees from the axial direction. The compressor efficiency was improved over a wide flow range especially under a high pressure ratio. The surge flow rate was reduced according to the increase in the VIGV setting angle. The maximum reduction rate of the surge flow rate was 14% compared to that without pre-whirl flow. By using VIGVs, the rotating stall accompanied by noise which usually occurs under a high pressure ratio and far from the surge was removed. Moreover, the design technology for a convex blade impeller was examined which consists of convex wingspans toward the rotational direction. The convex impeller has flexibility of changing the intermediate blade angle between the hub and the shroud independently. The convex impeller was designed to have a gradual change in blade-load and have mostly equal distributions between the full blades and splitter blades by utilizing a three-dimensional CFD. Compared with the straight blade impeller, a compressor with 5.5points higher efficiency has been developed.
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