For long time operation of general-use turbopumps with inducer, instability-free operation is expected as well as improved suction performance in the wide operating range from shut-off to over flow rates. However, the cavitation surge with strong inlet backflow often occurs in the low flow rate range. In our previous study, the effectiveness of the connecting with reduced-diameter suction pipe to inducer on the cavitation surge was experimentally investigated. Connecting with reduced-diameter suction pipe seems to have two effect : one is reducing the incidence angle by contracting the cross sectional area, another one is blocking the inlet backflow which extends along the casing wall. On the other hand, the same effects can be realized by the inducer design with small incidence angle. In the present paper, the effectiveness of the reduced-diameter suction pipe and that of the inducer designed with small incidence angle are compared in terms of the suction performance and the suppression of cavitation surge. As a result, the employment of reduced-diameter suction pipe achieves suction performance at moderate and higher flow rates with the narrowed onset region of cavitation surge. Further investigation is necessary for the quantitative assessment of suction performance at low flow rates due to the existence of strong swirling back flow.
