Effect of tip clearance on the operating mechanism of offset splitter blades in a centrifugal compressor

The good circumferential position of offset splitter blades and its mechanism were studied in small centrifugal impellers, which operated with different tip clearances by the computational fluid dynamics. When the impeller worked with the small tip clearance, the main loss was attributable to the separation near the main suction surfaces, and then the offset splitter bias toward the main suction surface can suppress this loss and enhance the impeller performance. The tip leakages increased with the tip clearance, so the loss concentrated in the passage between the main pressure surface and splitter, therefore the splitters tended to the main pressure surface, and then the offset splitters can reduce the concentration of the tip leakage and the loss. The tip clearance and the circumferential position of the splitter affected together the tip leakage, the separation near the suction surface and their interrelation. The design of the splitter circumferential position can adjust the crosswise pressure gradient in the blade passage and the location where the tip leakage mixes in the main flow, and then improve the ratio of the losses in the passages at both sides of splitter, therefore the best circumferential position of the splitter changes with the tip clearance.