In the industrial fields, the development of higher specific speed pumps is demanded with the importance of energy and resource savings. We believe that contra-rotating axial flow pumps with a rear rotor rotating opposite side to a front rotor offer a good solution against it. This type of the pump shows better performance and more compact machine size relatively than the conventional rotor-stator type under the same design specifications. In the present paper, the effect of rear-rotor speed on the hydraulic efficiency of contra-rotating axial flow pump is investigated by using numerical simulations. We re-designed several rear rotors with the different rotational speeds of Nr=600, 900 1123min−1 determined based on one-dimensional stream-tube theory with considering the momentum conservation laws. The evaluation of their performance is carried out by numerical simulations using ANSYS CFX. According to simulation results, it is found that the reduced rear-rotor speed concept brings about preferable performance with the increased efficiency. However, in the passage of re-designed rear rotors, secondary flow is clearly observed at the corner of hub and blade suction surfaces, indicating the possibility of further performance improvement with more appropriate blade design.

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