University of Novo mesto Faculty of Mechanical Engineering, Novo mesto, 8000, Slovenia
The operating range of centrifugal pumps is a very important information for the long service life and risks regarding various premature failures. The pump cannot always operate within the permitted range, for example, it must start and shut down the operation. When developing and selecting a pump, it is necessary to take into account the fact that the pump should be operated close to the best efficiency point (BEP) as often as possible. In this paper, we discuss the kinematic causes for the formation of the so-called hump zone in the pump H(Q) characteristic, where the flow rates are smaller than at the BEP. For the case of a reversible pump turbine, the detailed course of the pump characteristic at different relative openings of the guide vanes was numerically analyzed. The article presents the detailed flow field of velocity vectors and streamlines in front of the runner, inside the runner, and behind the runner.