Dynamic evolutions between the draft tube pressure pulsations and vortex ropes of a Francis turbine during runaway

Abstract

To analyze the dynamic evolutions between the draft tube pressure pulsations and vortex ropes of a Francis turbine, the runaway transient process of a hydropower system is simulated by coupling a one-dimensional model of the water conveyance system and a three-dimensional model of the Francis turbine. The results show that the annular-distributed pressure pattern at the entrance of the draft tube breaks and induces small vortex ropes, which then merge into an eccentric-distributed helical one with the transient operating point moving away from the rating region. In this process, low frequency pressure pulsations form and continue to strengthen. When the operating point moves to the runaway point, the vortex ropes keep dividing and merging irregularly, causing random-like pressure pulsations.