Author(s): B Nennemann; S Afara

Linked Author(s): Bernd Nennemann

Keywords: No Keywords

Abstract: The full load vortex in a hydraulic turbine can self-excite, leading to large synchronous pressure fluctuations that are transmitted to the entire hydraulic circuit resulting in potentially large power oscillations. Its root cause stems from the runner outlet area and the draft tube. Unsteady computational fluid dynamics (CFD) has proven successful at predicting many dynamic phenomena in hydraulic turbines. Our analyses show that this is also the case for the full load self-excitation of a medium to low head Francis model scale turbine. Our results indicate that blade outlet cavitation is present, when the cavitating full load vortex self-excites. Theoretical considerations show that for at least one type of self-excitation, a second elasticity, i.e. a second volume of cavitation, is a necessary condition, while an appropriate phase shift between the oscillations of the two elasticities will finally result in self-excitation.

DOI: https://doi.org/10.1088/1755-1315/1561/1/012025

Year: 2025