Author(s): Li Yanyan; Guo Pengcheng; Sun Longgang; Zheng Xiaobo

Linked Author(s): Pengcheng Guo

Keywords: Francis turbine; Runaway; Vortex; Pressure fluctuation

Abstract: The runaway process is a dynamic transition process that gradually deviates from the optimal operating condition. The flow passage components dissipate all of the energy corresponding to the hydraulic turbine's head, causing the internal flow of the hydraulic turbine to gradually deteriorate and produce a large-scale vortex structure during the runaway process. A model Francis turbine is used as the research object in this paper to understand the evolution characteristics of an unsteady vortex during a runaway. The runaway process is investigated using high-precision simulation technology of gas-liquid two-phase flow, and the runaway speed is obtained, consistent with the experimental results. The results show that the cavitation volume increases as the rotating speed increases. The large incidence angle between the inlet flow and the blade causes large-scale flow separation in the runner, which leads to forming of a sheet vortex band near the hub of the runner hub and a columnar vortex in the blade passage of the runner blade suction surface. As the runaway process continues, the flow separation in the runner intensifies and the induced vortex size increases, obstructing the runner's passage. In addition, pressure signal analysis reveals that the pressure fluctuation caused by the sheet vortex band is low-frequency. On the other hand, the pressure fluctuation caused by the columnar vortex is frequent. These two types of vortex structures with high-energy pressure fields degrade the flow in the runner and reduce the hydraulic performance of the turbine.

DOI: https://doi.org/10.1088/1742-6596/2752/1/012017

Year: 2023