The objective of this study is suppressing the diffuser rotating stall (DRS) for wide range from larger flow rate to shut off without reducing the maximum efficiency. Another objective is to confirm the effectiveness of the optimized diffuser vane slit by experiments and to clarify the mechanism of the DRS suppression by analyzing the flow in the vicinity of the slit, based on the Unsteady Reynolds-Averaged Navier-Stokes (URANS) calculation results.

As a result of a multi-objective optimization for the diffuser vane slit, the slit width, W = 9mm was comprehensively determined. As for the pump performance test, the diffuser with the optimized vane slit showed the stable head-flow performance curve compared to the diffuser with the original vane. It was clarified that the DRS onset flow rate of optimized shape shifted lower than original shape. As a result, the flow rate of the DRS onset could be shifted to the lower flow rate by 12%, and the operating range could be widened, though the pump efficiency decreased by 2.7% at the design flow rate.

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