Abstract
The contra-rotating rotor is effective for the down-sizing of the pump system. In the present study, since the reduced speed design of the rear rotor has been found to bring about higher hydraulic efficiency for contra-rotating axial flow pump, we design several rotors with different specific speeds of rear rotor to further examine the influence of rotor specific speed on hydraulic efficiency. It is found that the efficiency of rear rotor becomes better as the reduction of specific speed of rear rotor, whereas the efficiency of front rotor is deteriorated nevertheless of its constant specific speed, finally resulting in the maximum total efficiency at the moderate specific speed of rear rotor. Moreover, even though the rear rotor reveals the better efficiency with its reduced specific speed, the strong secondary flow is observed on the suction surface of rear rotor blade. More appropriate blade design seems to be necessary for further improving performance with the reduced specific speed design of the rear rotor.
