Abstract: For a high-head Francis pump turbine, the instability during operation is mainly caused by hydraulic vibrations inside the machine. As a major cause of vibrations, the pressure pulsation in the vaneless space can possibly lead to fatigue failure under certain circumstances. This paper studies the flow field and pressure pulsation in the vaneless space between the guide vanes and runner of a model pump turbine under the generation conditions, by combining numerical simulations and physical model tests. We focus on the amplitude-frequency characteristics of flow instability and pressure pulsation, and analyze their variations under different loads. We also examine the flow field in detail on a physical model using particle image velocimetry (PIV). The mechanism and development of vortices and its influence on pressure pulsation in the vaneless space are emphasized.

Key words: pressure pulsation, vaneless space, reversible pump turbine, PIV, numerical simulation