Abstract
A contra-rotating axial flow pump has been developed against demands for higher performance. Experiments were conducted to investigate effects of rotational speed control of the rear rotor on pump efficiency. The operating point with the maximum efficiency of the pump is discussed and the guiding principle of a rear rotor speed control is shown in the present paper. In the maximum efficiency point of the rear rotor, the relative flow smoothly enters the rear rotor passage at the inlet. This operating point is different from the maximum efficiency one of the pump and the circumferential velocity at the rear rotor exit, bringing about additional flow loss in downstream section, is still remained. When the zero circumferential velocity condition at the rear rotor exit, or the maximum pump efficiency condition is chosen by the rear rotor speed control, it is possible to improve the pump efficiency at the off-design point from that in the designed rotational speed.
