Experimental Investigations of Cavitation Characteristics of Pump Running in Turbine Mode

When a pump is running in turbine mode, susceptibility to cavitation increases, and it may be more severe than that in conventional hydro turbines. To accomplish the basic aim of making a compact machine with a high setting, a certain amount of cavitation can be allowed, then the erosion risk may be predicted. In the present study, experimental investigations were carried out on cavitation characteristics of a pump running in turbine mode in the nondimensional speed (N*) range of 0.64-1.07. For cavitation analysis, an additional suction creation system was installed, and different techniques were applied for cavitation detection viz pressure measurement, visual inspection, and vibration analysis. The performance of pump as turbine was found better in the N* of 0.71-0.86 in terms of higher efficiency and lesser possibility of cavitation. From the sigma test, the critical value of sigma was found as 0.595. The study revealed that, when a pump is operated as a turbine, it might be suffering from traveling bubble and von Karman vortex cavitation near impeller blades and vortex rope cavitation in the draft tube. (C) 2016 American Society of Civil Engineers.