Investigation of transient effects and energy losses for an axial flow pump as turbine in pump mode's start-up

In the start-up process of an axial flow pump as turbine under pump mode, the system exhibits unstable characteristics, leading to complex transient effects and significant energy losses. However, due to the lack of effective predictive methods, analyzing the transient performance of PAT systems remains challenging. To address this, this paper proposes a theoretical model for predicting the transient performance during the start-up of PAT pump mode and systematically analyzes the transient effects and energy losses using numerical simulation methods. The results indicate that both lag time and impact head are inversely proportional to start-up time, with shorter start-up times intensifying transient effects. Additionally, entropy production theory is employed to analyze energy losses in the PAT system, revealing a pattern of power losses that initially rise, then fall, and eventually stabilize, mirroring the trend in transient head. Further analysis demonstrates that the newly introduced method based on turbulent kinetic energy intensity provides higher accuracy in identifying energy loss distribution during the start-up process. This study offers valuable theoretical insights and methodological support for predicting transient performance and evaluating energy losses in hydraulic machinery during start-up.