Vibration and crack analysis of the runner chamber of bulb tubular turbine units

This study addresses intensified vibration and frequent cracking in the runner chamber of a bulb-type through-flow hydropower unit at Haibowan Hydropower Station. Combining on-site monitoring and numerical simulation, the research identifies that under high-head conditions, periodic pressure fluctuations—primarily from narrow-gap jetting between the runner blades and chamber—act as the principal excitation source at a frequency of four times the rotational speed (approximately 5.26 Hz). Although this frequency does not resonate with the natural structural frequencies, sustained alternating loads have induced high-cycle fatigue. Finite element analysis shows stress concentrations at ring rib welds and reinforcement zones, which are also the primary sites for crack initiation. Modal analysis confirms that despite the higher natural frequencies, the redundant ring rib structure fails to effectively distribute loads, leading to cascading crack propagation. These findings highlight potential fatigue failure risks under high load and non-design conditions, offering valuable insights for engineering applications and design optimization.