Abstract: When a Francis turbine operating in part-load, namely in a case of vortex zone, excessive pressure pulsations appear, which can lead to vibrations, noise, and power fluctuations, adversely affecting the unit′s safe and stable operation.In response to the sudden increase in pressure pulsation vibration, and noise in the vortex zone during model experiments, we investigated a large-scale medium-low-head Francis turbine operating in part-load in the vortex zone, and model tests and three-dimensional unsteady simulations (CFD) were employed to analyze the phenomena.The results revealed that the primary cause of the pressure pulsation surge was the 1.35 times rotational frequency pulsation induced by the thick and unstable vortex rope.Optimization of the runner and air supply were found to disrupt the unstable vortex rope, eliminating the 1.35 times rotational frequency component and significantly reducing pressure pulsations in the vortex zone.Additionally, matching different runner cones could weaken the intensity of the vortex rope (slightly narrowing the vortex rope), thus reducing the pressure pulsation amplitude, however, this modification cannot break the vortex and therefore the 1.35 times rotational frequency component remained.These findings can provide valuable insights for mitigating pressure pulsations in the vortex zone.In practical engineering, appropriate measures can be taken according to the actual situation.