Experimental analysis of a pump equipped with an axial rotor with variable speed

In hydropower systems among hydropower plants there are storage pump units. In order to ensure higher flow rate, the pumps have constructive differences besides regular. Consequently, the complex shape of the suction-elbow with symmetric inlet generates an unsteady flow which is ingested by impeller. These phenomena also generate stronger unsteady flow conditions, such as stall, wakes, turbulence and pressure fluctuations, which affect the overall mechanical behaviour of the pump with vibration, noise and radial and axial forces on the rotor. Alternatively, an axial rotor can be installed in front of the impeller. In this case, the non-uniformity flow will be decreased, and the static pressure will be increased at the impeller inlet. Consequently, the efficiency behaviour practically remains unchanged while the cavitational behaviour is improved. The paper investigates experimentally a pump system with the axial rotor having variable speed, while the pump impeller has constant speed. First, the paper presents the experimental test rig, the control and acquisition system. Second, is presented the pump system equipped with the clutch in order to have variable speed for the axial rotor. Thirdly, the experimental results concentrate on the axial rotor influence on the efficiency behaviour. The last section draws the conclusions.