Numerical simulation of the performance of a centrifugal pump with a semi-open impeller under normal and cavitating conditions

摘要

An important flow mechanism that can affect the performance and efficiency, as also the maintenance cost of centrifugal pumps is cavitation. Scientific research has been focusing on the mechanisms that govern cavitation in order to develop experimental and numerical tools that are able either to detect the phenomenon or to anticipate its appearance. In this study, a computational model is used in order to study the cavitation performance of a radial flow centrifugal pump with a semi open impeller. The numerical model includes and studies the effects of the blade tip clearance and its thickness, and it is validated against corresponding laboratory measurements and visualization data obtained for this pump under normal and cavitating flow conditions. The total head drop variation curves versus cavitation parameter are extracted both numerically and experimentally, and compared for various pump loading conditions with satisfactory agreement. A non-periodic pattern of flow and cavitation bubbles between the impeller blades, which is caused by the inlet pipe bending, is also well reproduced by the model. The numerical results display in detail the complex flow field and the secondary flows developed in the tip clearance area, close to the blades leading edge. The effects of the latter on the onset and development of cavitation at the suction side of the impeller, as well as on the backflow cavitation phenomenon are presented and analyzed. Backflow cavitation is found to affect the suction ability of the pump, especially for moderate cavitation conditions, as far as the pressure differences between the two blade sides remain significant.