Experiments are carried out to determine the effects of different inlet geometries on the onset of suction recirculation and its associated power consumption in an axial-flow pump. The critical flow rate is determined by both the “string” visual technique and “pressure” method. The results are correlated with the inlet area and flow velocity distribution upstream of the impeller. Four different conical covers matching the impeller leading edge are employed to cover the impeller inlet completely or partially. Covering the inlet area reduces the critical flowrate corresponding to the onset of suction recirculation and eliminates all recirculation at higher flowrates. The power consumption associated with the suction recirculation flow for the uncovered impeller is determined by comparing the shaft powers with and without inlet covers. At the shut-off condition, the power is estimated from a comparison with the shaft power measured with the impeller inlet completely covered. Experimental studies conclude that the power consumption due to suction recirculation is mainly controlled by the impeller inlet area and is insensitive to the inlet pipe configuration. At shut-off condition, the power coefficient correlates well with the parameter based on the hydraulic radius of inlet area. At a finite through flowrate the analytical model recommended by Tuzson (1983) is adequate, except for a proportionality coefficient determined from the test data.

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